Rough cut at async events

Directory.Build.props

@@ -15,6 +15,7 @@
     <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)build\Key.snk</AssemblyOriginatorKeyFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <AssemblySigningCertName>Microsoft</AssemblySigningCertName>
+    <LangVersion>7.3</LangVersion>
 
     <!-- Our customizations -->
     <SignAssembly>false</SignAssembly>

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorApi.cs

@@ -84,8 +84,6 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
             public static readonly string GetEventHandlerValue = "Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue";
 
-            public static readonly string SetValue = "Microsoft.AspNetCore.Blazor.Components.BindMethods.SetValue";
-
             public static readonly string SetValueHandler = "Microsoft.AspNetCore.Blazor.Components.BindMethods.SetValueHandler";
         }
 
@@ -93,10 +91,5 @@ namespace Microsoft.AspNetCore.Blazor.Razor
         {
             public static readonly string FullTypeName = "Microsoft.AspNetCore.Blazor.Components.EventHandlerAttribute";
         }
-
-        public static class UIEventHandler
-        {
-            public static readonly string FullTypeName = "Microsoft.AspNetCore.Blazor.UIEventHandler";
-        }
     }
 }

src/Microsoft.AspNetCore.Blazor.Templates/content/BlazorHosted.CSharp/BlazorHosted.CSharp.Client/BlazorHosted.CSharp.Client.csproj

@@ -8,6 +8,7 @@
       https://api.nuget.org/v3/index.json;
       https://dotnet.myget.org/f/blazor-dev/api/v3/index.json;
     </RestoreSources>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/Microsoft.AspNetCore.Blazor.Templates/content/BlazorHosted.CSharp/BlazorHosted.CSharp.Server/BlazorHosted.CSharp.Server.csproj

@@ -7,6 +7,7 @@
       https://api.nuget.org/v3/index.json;
       https://dotnet.myget.org/f/blazor-dev/api/v3/index.json;
     </RestoreSources>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(Framework)' != 'netcoreapp2.0'">

src/Microsoft.AspNetCore.Blazor.Templates/content/BlazorHosted.CSharp/BlazorHosted.CSharp.Shared/BlazorHosted.CSharp.Shared.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
 </Project>

src/Microsoft.AspNetCore.Blazor.Templates/content/BlazorLibrary.CSharp/BlazorLibrary.CSharp.csproj

@@ -10,6 +10,7 @@
       https://api.nuget.org/v3/index.json;
       https://dotnet.myget.org/f/blazor-dev/api/v3/index.json;
     </RestoreSources>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/Microsoft.AspNetCore.Blazor.Templates/content/BlazorStandalone.CSharp/BlazorStandalone.CSharp.csproj

@@ -9,6 +9,7 @@
       https://api.nuget.org/v3/index.json;
       https://dotnet.myget.org/f/blazor-dev/api/v3/index.json;
     </RestoreSources>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/Microsoft.AspNetCore.Blazor/Components/BindMethods.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Globalization;
+using System.Threading.Tasks;
 
 namespace Microsoft.AspNetCore.Blazor.Components
 {
@@ -41,6 +42,15 @@ namespace Microsoft.AspNetCore.Blazor.Components
             return value;
         }
 
+        /// <summary>
+        /// Not intended to be used directly.
+        /// </summary>
+        public static MulticastDelegate GetEventHandlerValue<T>(Func<Task> value)
+            where T : UIEventArgs
+        {
+            return value;
+        }
+
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
@@ -53,7 +63,16 @@ namespace Microsoft.AspNetCore.Blazor.Components
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler(Action<string> setter, string existingValue)
+        public static MulticastDelegate GetEventHandlerValue<T>(Func<T, Task> value)
+            where T : UIEventArgs
+        {
+            return value;
+        }
+
+        /// <summary>
+        /// Not intended to be used directly.
+        /// </summary>
+        public static Action<UIEventArgs> SetValueHandler(Action<string> setter, string existingValue)
         {
             return _ => setter((string)((UIChangeEventArgs)_).Value);
         }
@@ -61,7 +80,7 @@ namespace Microsoft.AspNetCore.Blazor.Components
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler(Action<bool> setter, bool existingValue)
+        public static Action<UIEventArgs> SetValueHandler(Action<bool> setter, bool existingValue)
         {
             return _ => setter((bool)((UIChangeEventArgs)_).Value);
         }
@@ -69,7 +88,7 @@ namespace Microsoft.AspNetCore.Blazor.Components
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler(Action<int> setter, int existingValue)
+        public static Action<UIEventArgs> SetValueHandler(Action<int> setter, int existingValue)
         {
             return _ => setter(int.Parse((string)((UIChangeEventArgs)_).Value));
         }
@@ -77,23 +96,23 @@ namespace Microsoft.AspNetCore.Blazor.Components
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler(Action<DateTime> setter, DateTime existingValue)
+        public static Action<UIEventArgs> SetValueHandler(Action<DateTime> setter, DateTime existingValue)
         {
-            return _ => SetDateTimeValue(setter, (object)((UIChangeEventArgs)_).Value, null);
+            return _ => SetDateTimeValue(setter, ((UIChangeEventArgs)_).Value, null);
         }
 
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler(Action<DateTime> setter, DateTime existingValue, string format)
+        public static Action<UIEventArgs> SetValueHandler(Action<DateTime> setter, DateTime existingValue, string format)
         {
-            return _ => SetDateTimeValue(setter, (object)((UIChangeEventArgs)_).Value, format);
+            return _ => SetDateTimeValue(setter, ((UIChangeEventArgs)_).Value, format);
         }
 
         /// <summary>
         /// Not intended to be used directly.
         /// </summary>
-        public static UIEventHandler SetValueHandler<T>(Action<T> setter, T existingValue)
+        public static Action<UIEventArgs> SetValueHandler<T>(Action<T> setter, T existingValue)
         {
             if (!typeof(T).IsEnum)
             {
@@ -108,52 +127,6 @@ namespace Microsoft.AspNetCore.Blazor.Components
             };
         }
 
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue(Action<string> setter, string existingValue)
-            => objValue => setter((string)objValue);
-
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue(Action<bool> setter, bool existingValue)
-            => objValue => setter((bool)objValue);
-
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue(Action<int> setter, int existingValue)
-            => objValue => setter(int.Parse((string)objValue));
-
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue<T>(Action<T> setter, T existingValue) => objValue =>
-        {
-            if (typeof(T).IsEnum)
-            {
-                var parsedValue = Enum.Parse(typeof(T), (string)objValue);
-                setter((T)parsedValue);
-            }
-            else
-            {
-                throw new ArgumentException($"@bind syntax does not accept values of type {typeof(T).FullName}. To read and write this value type, wrap it in a property of type string with suitable getters and setters.");
-            }
-        };
-
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue(Action<DateTime> setter, DateTime existingValue)
-            => objValue => SetDateTimeValue(setter, objValue, null);
-
-        /// <summary>
-        /// Not intended to be used directly.
-        /// </summary>
-        public static Action<object> SetValue(Action<DateTime> setter, DateTime existingValue, string format)
-            => objValue => SetDateTimeValue(setter, objValue, format);
-
         private static void SetDateTimeValue(Action<DateTime> setter, object objValue, string format)
         {
             var stringValue = (string)objValue;

src/Microsoft.AspNetCore.Blazor/Components/BlazorComponent.cs

@@ -175,14 +175,21 @@ namespace Microsoft.AspNetCore.Blazor.Components
             Console.Error.WriteLine($"[{ex.GetType().FullName}] {ex.Message}\n{ex.StackTrace}");
         }
 
-        void IHandleEvent.HandleEvent(UIEventHandler handler, UIEventArgs args)
+        void IHandleEvent.HandleEvent(EventHandlerInvoker binding, UIEventArgs args)
         {
-            handler(args);
+            var task = binding.Invoke(args);
 
             // After each event, we synchronously re-render (unless !ShouldRender())
             // This just saves the developer the trouble of putting "StateHasChanged();"
             // at the end of every event callback.
             StateHasChanged();
+            
+            if (task.Status == TaskStatus.RanToCompletion)
+            {
+                return;
+            }
+
+            task.ContinueWith(ContinueAfterLifecycleTask);
         }
     }
 }

src/Microsoft.AspNetCore.Blazor/Components/EventHandlerInvoker.cs

@@ -0,0 +1,55 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Blazor.Components
+{
+    /// <summary>
+    /// A bound event handler delegate.
+    /// </summary>
+    public struct EventHandlerInvoker
+    {
+        private readonly MulticastDelegate _delegate;
+
+        /// <summary>
+        /// Creates the new <see cref="EventHandlerInvoker"/>.
+        /// </summary>
+        /// <param name="delegate">The delegate to bind.</param>
+        public EventHandlerInvoker(MulticastDelegate @delegate)
+        {
+            _delegate = @delegate;
+        }
+        /// <summary>
+        /// Invokes the delegate associated with this binding.
+        /// </summary>
+        /// <param name="e">The <see cref="UIEventArgs"/>.</param>
+        /// <returns></returns>
+        public Task Invoke(UIEventArgs e)
+        {
+            switch (_delegate)
+            {
+                case Action action:
+                    action.Invoke();
+                    return Task.CompletedTask;
+
+                case Action<UIEventArgs> actionEventArgs:
+                    actionEventArgs.Invoke(e);
+                    return Task.CompletedTask;
+
+                case Func<Task> func:
+                    return func.Invoke();
+
+                case Func<UIEventArgs, Task> funcEventArgs:
+                    return funcEventArgs.Invoke(e);
+
+                case MulticastDelegate @delegate:
+                    return @delegate.DynamicInvoke(e) as Task ?? Task.CompletedTask;
+
+                case null:
+                    return Task.CompletedTask;
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Blazor/Components/IHandleEvent.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNetCore.Blazor.RenderTree;
-
 namespace Microsoft.AspNetCore.Blazor.Components
 {
     /// <summary>
@@ -13,8 +11,8 @@ namespace Microsoft.AspNetCore.Blazor.Components
         /// <summary>
         /// Notifies the component that one of its event handlers has been triggered.
         /// </summary>
-        /// <param name="handler">The event handler.</param>
+        /// <param name="binding">The event binding.</param>
         /// <param name="args">Arguments for the event handler.</param>
-        void HandleEvent(UIEventHandler handler, UIEventArgs args);
+        void HandleEvent(EventHandlerInvoker binding, UIEventArgs args);
     }
 }

src/Microsoft.AspNetCore.Blazor/Microsoft.AspNetCore.Blazor.csproj

@@ -2,7 +2,6 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <LangVersion>7.2</LangVersion>
   </PropertyGroup>
 
 </Project>

src/Microsoft.AspNetCore.Blazor/RenderTree/RenderTreeBuilder.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.Rendering;
 
@@ -167,7 +168,7 @@ namespace Microsoft.AspNetCore.Blazor.RenderTree
 
         /// <summary>
         /// <para>
-        /// Appends a frame representing an <see cref="UIEventHandler"/>-valued attribute.
+        /// Appends a frame representing an <see cref="Action{UIEventArgs}"/>-valued attribute.
         /// </para>
         /// <para>
         /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
@@ -177,7 +178,41 @@ namespace Microsoft.AspNetCore.Blazor.RenderTree
         /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
         /// <param name="name">The name of the attribute.</param>
         /// <param name="value">The value of the attribute.</param>
-        public void AddAttribute(int sequence, string name, UIEventHandler value)
+        public void AddAttribute(int sequence, string name, Action<UIEventArgs> value)
+        {
+            AddAttribute(sequence, name, (MulticastDelegate)value);
+        }
+
+        /// <summary>
+        /// <para>
+        /// Appends a frame representing a <see cref="Func{Task}"/>-valued attribute.
+        /// </para>
+        /// <para>
+        /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
+        /// current element is not a component, the frame will be omitted.
+        /// </para>
+        /// </summary>
+        /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
+        /// <param name="name">The name of the attribute.</param>
+        /// <param name="value">The value of the attribute.</param>
+        public void AddAttribute(int sequence, string name, Func<Task> value)
+        {
+            AddAttribute(sequence, name, (MulticastDelegate)value);
+        }
+
+        /// <summary>
+        /// <para>
+        /// Appends a frame representing a <see cref="Func{UIEventArgs, Task}"/>-valued attribute.
+        /// </para>
+        /// <para>
+        /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
+        /// current element is not a component, the frame will be omitted.
+        /// </para>
+        /// </summary>
+        /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
+        /// <param name="name">The name of the attribute.</param>
+        /// <param name="value">The value of the attribute.</param>
+        public void AddAttribute(int sequence, string name, Func<UIEventArgs, Task> value)
         {
             AddAttribute(sequence, name, (MulticastDelegate)value);
         }
@@ -196,10 +231,10 @@ namespace Microsoft.AspNetCore.Blazor.RenderTree
         /// <param name="value">The value of the attribute.</param>
         /// <remarks>
         /// This method is provided for infrastructure purposes, and is used to be
-        /// <see cref="UIEventHandlerRenderTreeBuilderExtensions"/> to provide support for delegates of specific
+        /// <see cref="UIEventArgsRenderTreeBuilderExtensions"/> to provide support for delegates of specific
         /// types. For a good programming experience when using a custom delegate type, define an
         /// extension method similar to 
-        /// <see cref="UIEventHandlerRenderTreeBuilderExtensions.AddAttribute(RenderTreeBuilder, int, string, UIChangeEventHandler)"/>
+        /// <see cref="UIEventArgsRenderTreeBuilderExtensions.AddAttribute(RenderTreeBuilder, int, string, Action{UIChangeEventArgs})"/>
         /// that calls this method.
         /// </remarks>
         public void AddAttribute(int sequence, string name, MulticastDelegate value)

src/Microsoft.AspNetCore.Blazor/RenderTree/RenderTreeFrame.cs

@@ -195,7 +195,7 @@ namespace Microsoft.AspNetCore.Blazor.RenderTree
         internal static RenderTreeFrame Text(int sequence, string textContent)
             => new RenderTreeFrame(sequence, textContent: textContent);
 
-        internal static RenderTreeFrame Attribute(int sequence, string name, UIEventHandler value)
+        internal static RenderTreeFrame Attribute(int sequence, string name, MulticastDelegate value)
              => new RenderTreeFrame(sequence, attributeName: name, attributeValue: value);
 
         internal static RenderTreeFrame Attribute(int sequence, string name, object value)

src/Microsoft.AspNetCore.Blazor/Rendering/ComponentState.cs

@@ -1,9 +1,9 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.RenderTree;
-using System;
 
 namespace Microsoft.AspNetCore.Blazor.Rendering
 {
@@ -73,11 +73,11 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
             RenderTreeDiffBuilder.DisposeFrames(batchBuilder, _renderTreeBuilderCurrent.GetFrames());
         }
 
-        public void DispatchEvent(UIEventHandler handler, UIEventArgs eventArgs)
+        public void DispatchEvent(EventHandlerInvoker binding, UIEventArgs eventArgs)
         {
             if (_component is IHandleEvent handleEventComponent)
             {
-                handleEventComponent.HandleEvent(handler, eventArgs);
+                handleEventComponent.HandleEvent(binding, eventArgs);
             }
             else
             {

src/Microsoft.AspNetCore.Blazor/Rendering/Renderer.cs

@@ -5,6 +5,7 @@ using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.RenderTree;
 using System;
 using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace Microsoft.AspNetCore.Blazor.Rendering
 {
@@ -23,8 +24,7 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
         private bool _isBatchInProgress;
 
         private int _lastEventHandlerId = 0;
-        private readonly Dictionary<int, UIEventHandler> _eventHandlersById
-            = new Dictionary<int, UIEventHandler>();
+        private readonly Dictionary<int, EventHandlerInvoker> _eventBindings = new Dictionary<int, EventHandlerInvoker>();
 
         /// <summary>
         /// Constructs an instance of <see cref="Renderer"/>.
@@ -72,14 +72,14 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
         /// <param name="eventArgs">Arguments to be passed to the event handler.</param>
         protected void DispatchEvent(int componentId, int eventHandlerId, UIEventArgs eventArgs)
         {
-            if (_eventHandlersById.TryGetValue(eventHandlerId, out var handler))
+            if (_eventBindings.TryGetValue(eventHandlerId, out var binding))
             {
                 // The event handler might request multiple renders in sequence. Capture them
                 // all in a single batch.
                 try
                 {
                     _isBatchInProgress = true;
-                    GetRequiredComponentState(componentId).DispatchEvent(handler, eventArgs);
+                    GetRequiredComponentState(componentId).DispatchEvent(binding, eventArgs);
                 }
                 finally
                 {
@@ -114,32 +114,9 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
         {
             var id = ++_lastEventHandlerId;
 
-            // The attribute value might be a more specialized type like UIKeyboardEventHandler.
-            // In that case, it won't be a UIEventHandler, and it will go down the MulticastDelegate
-            // code path (MulticastDelegate is any delegate).
-            //
-            // In order to dispatch the event, we need a UIEventHandler, so we're going weakly
-            // typed here. The user will get a cast exception if they map the wrong type of
-            // delegate to the event.
-            if (frame.AttributeValue is UIEventHandler wrapper)
+            if (frame.AttributeValue is MulticastDelegate @delegate)
             {
-                _eventHandlersById.Add(id, wrapper);
-            }
-            // IMPORTANT: we're creating an additional delegate when necessary. This is
-            // going to get cached in _eventHandlersById, but the render tree diff
-            // will operate on 'AttributeValue' which means that we'll only create a new
-            // wrapper delegate when the underlying delegate changes.
-            //
-            // TLDR: If the component uses a method group or a non-capturing lambda
-            // we don't allocate much.
-            else if (frame.AttributeValue is Action action)
-            {
-                _eventHandlersById.Add(id, (UIEventArgs e) => action());
-            }
-            else if (frame.AttributeValue is MulticastDelegate @delegate)
-            {
-
-               _eventHandlersById.Add(id, (UIEventArgs e) => @delegate.DynamicInvoke(e));
+               _eventBindings.Add(id, new EventHandlerInvoker(@delegate));
             }
 
             frame = frame.WithAttributeEventHandlerId(id);
@@ -218,7 +195,7 @@ namespace Microsoft.AspNetCore.Blazor.Rendering
             var count = eventHandlerIds.Count;
             for (var i = 0; i < count; i++)
             {
-                _eventHandlersById.Remove(array[i]);
+                _eventBindings.Remove(array[i]);
             }
         }
     }

src/Microsoft.AspNetCore.Blazor/UIEventArgsRenderTreeBuilderExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Blazor.RenderTree;
 
 namespace Microsoft.AspNetCore.Blazor
@@ -35,11 +36,11 @@ namespace Microsoft.AspNetCore.Blazor
     /// </code>
     /// </para>
     /// </remarks>
-    public static class UIEventHandlerRenderTreeBuilderExtensions
+    public static class UIEventArgsRenderTreeBuilderExtensions
     {
         /// <summary>
         /// <para>
-        /// Appends a frame representing an <see cref="UIChangeEventArgs"/>-valued attribute.
+        /// Appends a frame representing an <see cref="Action{UIChangeEventArgs}"/>-valued attribute.
         /// </para>
         /// <para>
         /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
@@ -50,7 +51,7 @@ namespace Microsoft.AspNetCore.Blazor
         /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
         /// <param name="name">The name of the attribute.</param>
         /// <param name="value">The value of the attribute.</param>
-        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, UIChangeEventHandler value)
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Action<UIChangeEventArgs> value)
         {
             if (builder == null)
             {
@@ -62,7 +63,7 @@ namespace Microsoft.AspNetCore.Blazor
 
         /// <summary>
         /// <para>
-        /// Appends a frame representing an <see cref="UIKeyboardEventHandler"/>-valued attribute.
+        /// Appends a frame representing an <see cref="Func{UIChangeEventArgs, Task}"/>-valued attribute.
         /// </para>
         /// <para>
         /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
@@ -73,7 +74,7 @@ namespace Microsoft.AspNetCore.Blazor
         /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
         /// <param name="name">The name of the attribute.</param>
         /// <param name="value">The value of the attribute.</param>
-        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, UIKeyboardEventHandler value)
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Func<UIChangeEventArgs, Task> value)
         {
             if (builder == null)
             {
@@ -85,7 +86,7 @@ namespace Microsoft.AspNetCore.Blazor
 
         /// <summary>
         /// <para>
-        /// Appends a frame representing an <see cref="UIMouseEventHandler"/>-valued attribute.
+        /// Appends a frame representing an <see cref="Action{UIKeyboardEventArgs}"/>-valued attribute.
         /// </para>
         /// <para>
         /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
@@ -96,7 +97,76 @@ namespace Microsoft.AspNetCore.Blazor
         /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
         /// <param name="name">The name of the attribute.</param>
         /// <param name="value">The value of the attribute.</param>
-        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, UIMouseEventHandler value)
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Action<UIKeyboardEventArgs> value)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.AddAttribute(sequence, name, (MulticastDelegate)value);
+        }
+
+        /// <summary>
+        /// <para>
+        /// Appends a frame representing an <see cref="Func{UIKeyboardEventArgs, Task}"/>-valued attribute.
+        /// </para>
+        /// <para>
+        /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
+        /// current element is not a component, the frame will be omitted.
+        /// </para>
+        /// </summary>
+        /// <param name="builder">The <see cref="RenderTreeBuilder"/>.</param>
+        /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
+        /// <param name="name">The name of the attribute.</param>
+        /// <param name="value">The value of the attribute.</param>
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Func<UIKeyboardEventArgs, Task> value)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.AddAttribute(sequence, name, (MulticastDelegate)value);
+        }
+
+        /// <summary>
+        /// <para>
+        /// Appends a frame representing an <see cref="Action{UIMouseEventArgs}"/>-valued attribute.
+        /// </para>
+        /// <para>
+        /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
+        /// current element is not a component, the frame will be omitted.
+        /// </para>
+        /// </summary>
+        /// <param name="builder">The <see cref="RenderTreeBuilder"/>.</param>
+        /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
+        /// <param name="name">The name of the attribute.</param>
+        /// <param name="value">The value of the attribute.</param>
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Action<UIMouseEventArgs> value)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.AddAttribute(sequence, name, (MulticastDelegate)value);
+        }
+
+        /// <summary>
+        /// <para>
+        /// Appends a frame representing an <see cref="Func{UIMouseEventArgs, Task}"/>-valued attribute.
+        /// </para>
+        /// <para>
+        /// The attribute is associated with the most recently added element. If the value is <c>null</c> and the
+        /// current element is not a component, the frame will be omitted.
+        /// </para>
+        /// </summary>
+        /// <param name="builder">The <see cref="RenderTreeBuilder"/>.</param>
+        /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
+        /// <param name="name">The name of the attribute.</param>
+        /// <param name="value">The value of the attribute.</param>
+        public static void AddAttribute(this RenderTreeBuilder builder, int sequence, string name, Func<UIMouseEventArgs, Task> value)
         {
             if (builder == null)
             {

src/Microsoft.AspNetCore.Blazor/UIEventHandler.cs

@@ -1,27 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Blazor.RenderTree;
-
-namespace Microsoft.AspNetCore.Blazor
-{
-    /// <summary>
-    /// Handles an <see cref="UIEventArgs"/> event raised for a <see cref="RenderTreeFrame"/>.
-    /// </summary>
-    public delegate void UIEventHandler(UIEventArgs e);
-
-    /// <summary>
-    /// Handles an <see cref="UIChangeEventArgs"/> event raised for a <see cref="RenderTreeFrame"/>.
-    /// </summary>
-    public delegate void UIChangeEventHandler(UIChangeEventArgs e);
-
-    /// <summary>
-    /// Handles an <see cref="UIKeyboardEventArgs"/> event raised for a <see cref="RenderTreeFrame"/>.
-    /// </summary>
-    public delegate void UIKeyboardEventHandler(UIKeyboardEventArgs e);
-
-    /// <summary>
-    /// Handles an <see cref="UIMouseEventArgs"/> event raised for a <see cref="RenderTreeFrame"/>.
-    /// </summary>
-    public delegate void UIMouseEventHandler(UIMouseEventArgs e);
-}

test/Microsoft.AspNetCore.Blazor.Build.Test/BindRazorIntegrationTest.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         public void Render_BindToComponent_SpecifiesValue_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -52,7 +52,7 @@ namespace Test
         public void Render_BindToComponent_SpecifiesValue_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -81,14 +81,14 @@ namespace Test
                 frames,
                 frame => AssertFrame.Component(frame, "Test.MyComponent", 3, 0),
                 frame => AssertFrame.Attribute(frame, "Value", 42, 1),
-                frame => AssertFrame.Attribute(frame, "ValueChanged", typeof(UIEventHandler), 2));
+                frame => AssertFrame.Attribute(frame, "ValueChanged", typeof(Action<UIEventArgs>), 2));
         }
 
         [Fact]
         public void Render_BindToComponent_SpecifiesValueAndChangeEvent_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -124,7 +124,7 @@ namespace Test
         public void Render_BindToComponent_SpecifiesValueAndChangeEvent_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -153,14 +153,14 @@ namespace Test
                 frames,
                 frame => AssertFrame.Component(frame, "Test.MyComponent", 3, 0),
                 frame => AssertFrame.Attribute(frame, "Value", 42, 1),
-                frame => AssertFrame.Attribute(frame, "OnChanged", typeof(UIEventHandler), 2));
+                frame => AssertFrame.Attribute(frame, "OnChanged", typeof(Action<UIEventArgs>), 2));
         }
 
         [Fact]
         public void Render_BindToElement_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -187,14 +187,14 @@ namespace Test
                 frames,
                 frame => AssertFrame.Element(frame, "div", 3, 0),
                 frame => AssertFrame.Attribute(frame, "myvalue", "hi", 1),
-                frame => AssertFrame.Attribute(frame, "myevent", typeof(UIEventHandler), 2));
+                frame => AssertFrame.Attribute(frame, "myevent", typeof(Action<UIEventArgs>), 2));
         }
 
         [Fact]
         public void Render_BindToElementWithSuffix_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -221,14 +221,14 @@ namespace Test
                 frames,
                 frame => AssertFrame.Element(frame, "div", 3, 0),
                 frame => AssertFrame.Attribute(frame, "myvalue", "hi", 1),
-                frame => AssertFrame.Attribute(frame, "myevent", typeof(UIEventHandler), 2));
+                frame => AssertFrame.Attribute(frame, "myevent", typeof(Action<UIEventArgs>), 2));
         }
 
         [Fact]
         public void Render_BindDuplicates_ReportsDiagnostic()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -278,7 +278,7 @@ namespace Test
                 frames,
                 frame => AssertFrame.Element(frame, "input", 3, 0),
                 frame => AssertFrame.Attribute(frame, "value", "42", 1),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 2));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 2));
         }
 
         [Fact]
@@ -301,7 +301,7 @@ namespace Test
                 frame => AssertFrame.Element(frame, "input", 4, 0),
                 frame => AssertFrame.Attribute(frame, "type", "text", 1),
                 frame => AssertFrame.Attribute(frame, "value", new DateTime(2018, 1, 1).ToString("MM/dd/yyyy"), 2),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact]
@@ -326,7 +326,7 @@ namespace Test
                 frame => AssertFrame.Element(frame, "input", 4, 0),
                 frame => AssertFrame.Attribute(frame, "type", "text", 1),
                 frame => AssertFrame.Attribute(frame, "value", new DateTime(2018, 1, 1).ToString("MM/dd/yyyy"), 2),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact]
@@ -349,7 +349,7 @@ namespace Test
                 frame => AssertFrame.Element(frame, "input", 4, 0),
                 frame => AssertFrame.Attribute(frame, "type", "text", 1),
                 frame => AssertFrame.Attribute(frame, "value", "42", 2),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact]
@@ -371,7 +371,7 @@ namespace Test
                 frames,
                 frame => AssertFrame.Element(frame, "input", 3, 0),
                 frame => AssertFrame.Attribute(frame, "type", "checkbox", 1),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact]
@@ -394,7 +394,7 @@ namespace Test
                 frame => AssertFrame.Element(frame, "input", 4, 0),
                 frame => AssertFrame.Attribute(frame, "type", "text", 1),
                 frame => AssertFrame.Attribute(frame, "value", "42", 2),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact]
@@ -417,7 +417,7 @@ namespace Test
                 frame => AssertFrame.Element(frame, "input", 4, 0),
                 frame => AssertFrame.Attribute(frame, "type", "text", 1),
                 frame => AssertFrame.Attribute(frame, "value", new DateTime(2018, 1, 1).ToString("MM/dd"), 2),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 3));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 3));
         }
 
         [Fact] // Additional coverage of OrphanTagHelperLoweringPass
@@ -441,7 +441,7 @@ namespace Test
                 frame => AssertFrame.Attribute(frame, "visible", 1), // This gets reordered in the node writer
                 frame => AssertFrame.Attribute(frame, "type", "text", 2),
                 frame => AssertFrame.Attribute(frame, "value", "42", 3),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 4));
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 4));
         }
 
         [Fact] // Additional coverage of OrphanTagHelperLoweringPass
@@ -465,7 +465,7 @@ namespace Test
                 frames,
                 frame => AssertFrame.Element(frame, "div", 7, 0),
                 frame => AssertFrame.Attribute(frame, "value", "42", 1),
-                frame => AssertFrame.Attribute(frame, "onchange", typeof(UIEventHandler), 2),
+                frame => AssertFrame.Attribute(frame, "onchange", typeof(Action<UIEventArgs>), 2),
                 frame => AssertFrame.Whitespace(frame, 3),
                 frame => AssertFrame.Element(frame, "span", 2, 4),
                 frame => AssertFrame.Text(frame, "42", 5),

test/Microsoft.AspNetCore.Blazor.Build.Test/ComponentDiscoveryRazorIntegrationTest.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         public void ComponentDiscovery_CanFindComponent_DefinedinCSharp()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -41,7 +41,7 @@ namespace Test
         public void ComponentDiscovery_CanFindComponent_WithNamespace_DefinedinCSharp()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test.AnotherNamespace

test/Microsoft.AspNetCore.Blazor.Build.Test/ComponentRenderingRazorIntegrationTest.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         public void Render_ChildComponent_Simple()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -46,7 +46,7 @@ namespace Test
         public void Render_ChildComponent_WithParameters()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -94,7 +94,7 @@ namespace Test
         public void Render_ChildComponent_WithExplicitStringParameter()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -124,7 +124,7 @@ namespace Test
         public void Render_ChildComponent_WithNonPropertyAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -165,7 +165,7 @@ namespace Test
         public void Render_ChildComponent_WithEventHandler(string expression)
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -174,7 +174,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIMouseEventHandler OnClick { get; set; }
+        public Action<UIMouseEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -203,7 +203,7 @@ namespace Test
                     AssertFrame.Attribute(frame, "OnClick", 1);
 
                     // The handler will have been assigned to a lambda
-                    var handler = Assert.IsType<UIMouseEventHandler>(frame.AttributeValue);
+                    var handler = Assert.IsType<Action<UIMouseEventArgs>>(frame.AttributeValue);
                     Assert.Equal("Test.TestComponent", handler.Target.GetType().FullName);
                 });
         }
@@ -212,7 +212,7 @@ namespace Test
         public void Render_ChildComponent_WithExplicitEventHandler()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -221,7 +221,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -250,7 +250,7 @@ namespace Test
                     AssertFrame.Attribute(frame, "OnClick", 1);
 
                     // The handler will have been assigned to a lambda
-                    var handler = Assert.IsType<UIEventHandler>(frame.AttributeValue);
+                    var handler = Assert.IsType<Action<UIEventArgs>>(frame.AttributeValue);
                     Assert.Equal("Test.TestComponent", handler.Target.GetType().FullName);
                     Assert.Equal("Increment", handler.Method.Name);
                 });
@@ -260,7 +260,7 @@ namespace Test
         public void Render_ChildComponent_WithMinimizedBoolAttribute()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -289,7 +289,7 @@ namespace Test
         public void Render_ChildComponent_WithChildContent()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
 namespace Test
@@ -330,7 +330,7 @@ namespace Test
         public void Render_ChildComponent_Nested()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
 

test/Microsoft.AspNetCore.Blazor.Build.Test/DesignTimeCodeGenerationTest.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         public void ChildComponent_WithParameters()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -54,7 +54,7 @@ namespace Test
         public void ChildComponent_WithExplicitStringParameter()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -81,7 +81,7 @@ namespace Test
         public void ChildComponent_WithNonPropertyAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -107,7 +107,7 @@ namespace Test
         public void ChildComponent_WithLambdaEventHandler()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -116,7 +116,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -143,7 +143,7 @@ namespace Test
         public void ChildComponent_WithExplicitEventHandler()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -152,7 +152,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -180,7 +180,7 @@ namespace Test
         public void ChildComponent_WithChildContent()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -257,11 +257,93 @@ namespace Test
             CompileToAssembly(generated);
         }
 
+        [Fact]
+        public void AsyncEventHandler_OnElement_Action_MethodGroup()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""@OnClick"" />
+@functions {
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+}");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""@OnClick"" />
+@functions {
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+}");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_Action_Lambda()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""async (e) => await Task.Delay(10)"" />
+");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_ActionEventArgs_Lambda()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""async (e) => await Task.Delay(10)"" />
+");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
         [Fact] // https://github.com/aspnet/Blazor/issues/597
         public void Regression_597()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -292,7 +374,7 @@ namespace Test
         public void BindToComponent_SpecifiesValue_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -324,7 +406,7 @@ namespace Test
         public void BindToComponent_SpecifiesValue_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -356,7 +438,7 @@ namespace Test
         public void BindToComponent_SpecifiesValueAndChangeEvent_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -387,7 +469,7 @@ namespace Test
         public void BindToComponent_SpecifiesValueAndChangeEvent_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -418,7 +500,7 @@ namespace Test
         public void BindToElement_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -448,7 +530,7 @@ namespace Test
         public void BindToElementWithSuffix_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 

test/Microsoft.AspNetCore.Blazor.Build.Test/Microsoft.AspNetCore.Blazor.Build.Test.csproj

@@ -19,7 +19,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.6.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.8.0-beta3" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
     <PackageReference Include="xunit" Version="2.3.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />

test/Microsoft.AspNetCore.Blazor.Build.Test/RazorIntegrationTestBase.cs

@@ -32,6 +32,8 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         // so making sure it doesn't happen for each test.
         private static readonly CSharpCompilation BaseCompilation;
 
+        private static CSharpParseOptions CSharpParseOptions { get; }
+
         static RazorIntegrationTestBase()
         {
             var referenceAssemblyRoots = new[]
@@ -52,6 +54,8 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                 Array.Empty<SyntaxTree>(),
                 referenceAssemblies,
                 new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+
+            CSharpParseOptions = new CSharpParseOptions(LanguageVersion.CSharp7_3);
         }
 
         public RazorIntegrationTestBase()
@@ -59,6 +63,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             AdditionalSyntaxTrees = new List<SyntaxTree>();
             AdditionalRazorItems = new List<RazorProjectItem>();
 
+            
             Configuration = BlazorExtensionInitializer.DefaultConfiguration;
             FileSystem = new VirtualRazorProjectFileSystem();
             PathSeparator = Path.DirectorySeparatorChar.ToString();
@@ -162,7 +167,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     codeDocument = projectEngine.Process(item);
                     Assert.Empty(codeDocument.GetCSharpDocument().Diagnostics);
 
-                    var syntaxTree = CSharpSyntaxTree.ParseText(codeDocument.GetCSharpDocument().GeneratedCode, path: item.FilePath);
+                    var syntaxTree = Parse(codeDocument.GetCSharpDocument().GeneratedCode, path: item.FilePath);
                     AdditionalSyntaxTrees.Add(syntaxTree);
                 }
 
@@ -192,7 +197,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     Assert.Empty(codeDocument.GetCSharpDocument().Diagnostics);
 
                     // Replace the 'declaration' syntax tree
-                    var syntaxTree = CSharpSyntaxTree.ParseText(codeDocument.GetCSharpDocument().GeneratedCode, path: item.FilePath);
+                    var syntaxTree = Parse(codeDocument.GetCSharpDocument().GeneratedCode, path: item.FilePath);
                     AdditionalSyntaxTrees.RemoveAll(st => st.FilePath == item.FilePath);
                     AdditionalSyntaxTrees.Add(syntaxTree);
                 }
@@ -241,7 +246,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
 
             var syntaxTrees = new[]
             {
-                CSharpSyntaxTree.ParseText(cSharpResult.Code),
+                Parse(cSharpResult.Code),
             };
 
             var compilation = cSharpResult.BaseCompilation.AddSyntaxTrees(syntaxTrees);
@@ -274,7 +279,6 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     Assembly = diagnostics.Any() ? null : Assembly.Load(peStream.ToArray())
                 };
             }
-
         }
 
         protected IComponent CompileToComponent(string cshtmlSource)
@@ -303,6 +307,11 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             return (IComponent)Activator.CreateInstance(componentType);
         }
 
+        protected static CSharpSyntaxTree Parse(string text, string path = null)
+        {
+            return (CSharpSyntaxTree)CSharpSyntaxTree.ParseText(text, CSharpParseOptions, path: path);
+        }
+
         protected static string FullTypeName<T>() => typeof(T).FullName.Replace('+', '.');
 
         protected RenderTreeFrame[] GetRenderTree(IComponent component)

test/Microsoft.AspNetCore.Blazor.Build.Test/RenderingRazorIntegrationTest.cs

@@ -306,7 +306,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     Assert.Equal(1, frame.Sequence);
                     Assert.NotNull(frame.AttributeValue);
 
-                    ((UIEventHandler)frame.AttributeValue)(null);
+                    ((Action<UIEventArgs>)frame.AttributeValue)(null);
                     Assert.True((bool)handlerWasCalledProperty.GetValue(component));
                 });
         }
@@ -346,7 +346,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     AssertFrame.Attribute(frame, "onchange", 2);
 
                     // Trigger the change event to show it updates the property
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = "Modified value"
                     });
@@ -375,7 +375,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     AssertFrame.Attribute(frame, "onchange", 2);
 
                     // Trigger the change event to show it updates the property
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = "Modified value"
                     });
@@ -405,7 +405,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
 
                     // Trigger the change event to show it updates the property
                     var newDateValue = new DateTime(2018, 3, 5, 4, 5, 6);
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = newDateValue.ToString()
                     });
@@ -435,7 +435,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     AssertFrame.Attribute(frame, "onchange", 2);
 
                     // Trigger the change event to show it updates the property
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = new DateTime(2018, 3, 5).ToString(testDateFormat)
                     });
@@ -542,7 +542,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     AssertFrame.Attribute(frame, "onchange", 2);
 
                     // Trigger the change event to show it updates the property
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = false
                     });
@@ -572,7 +572,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                     AssertFrame.Attribute(frame, "onchange", 2);
 
                     // Trigger the change event to show it updates the property
-                    ((UIEventHandler)frame.AttributeValue)(new UIChangeEventArgs
+                    ((Action<UIEventArgs>)frame.AttributeValue)(new UIChangeEventArgs
                     {
                         Value = MyEnum.SecondValue.ToString()
                     });

test/Microsoft.AspNetCore.Blazor.Build.Test/RuntimeCodeGenerationTest.cs

@@ -14,7 +14,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
         public void ChildComponent_Simple()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -40,7 +40,7 @@ namespace Test
         public void ChildComponent_WithParameters()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -78,7 +78,7 @@ namespace Test
         public void ChildComponent_WithExplicitStringParameter()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -105,7 +105,7 @@ namespace Test
         public void ChildComponent_WithNonPropertyAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -132,7 +132,7 @@ namespace Test
         public void ChildComponent_WithLambdaEventHandler()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -141,7 +141,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -168,7 +168,7 @@ namespace Test
         public void ChildComponent_WithExplicitEventHandler()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -177,7 +177,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIEventArgs> OnClick { get; set; }
     }
 }
 "));
@@ -205,7 +205,7 @@ namespace Test
         public void ChildComponent_WithChildContent()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -235,7 +235,7 @@ namespace Test
         public void ChildComponent_WithPageDirective()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -366,6 +366,88 @@ namespace Test
             CompileToAssembly(generated);
         }
 
+        [Fact]
+        public void AsyncEventHandler_OnElement_Action_MethodGroup()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""@OnClick"" />
+@functions {
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+}");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""@OnClick"" />
+@functions {
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+}");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_Action_Lambda()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""async (e) => await Task.Delay(10)"" />
+");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
+        [Fact]
+        public void AsyncEventHandler_OnElement_ActionEventArgs_Lambda()
+        {
+            // Arrange
+
+            // Act
+            var generated = CompileToCSharp(@"
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+<input onclick=""async (e) => await Task.Delay(10)"" />
+");
+
+            // Assert
+            AssertDocumentNodeMatchesBaseline(generated.CodeDocument);
+            AssertCSharpDocumentMatchesBaseline(generated.CodeDocument);
+            CompileToAssembly(generated);
+        }
+
         [Fact]
         public void ScriptTag_WithErrorSuppressed()
         {
@@ -421,7 +503,7 @@ namespace Test
         public void LeadingWhiteSpace_WithComponent()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -484,7 +566,7 @@ namespace Test
         public void TrailingWhiteSpace_WithComponent()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -514,7 +596,7 @@ namespace Test
         public void Regression_597()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -545,7 +627,7 @@ namespace Test
         public void BindToComponent_SpecifiesValue_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -577,7 +659,7 @@ namespace Test
         public void BindToComponent_SpecifiesValue_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -609,7 +691,7 @@ namespace Test
         public void BindToComponent_SpecifiesValueAndChangeEvent_WithMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -640,7 +722,7 @@ namespace Test
         public void BindToComponent_SpecifiesValueAndChangeEvent_WithoutMatchingProperties()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -671,7 +753,7 @@ namespace Test
         public void BindToElement_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -701,7 +783,7 @@ namespace Test
         public void BindToElementWithSuffix_WritesAttributes()
         {
             // Arrange
-            AdditionalSyntaxTrees.Add(CSharpSyntaxTree.ParseText(@"
+            AdditionalSyntaxTrees.Add(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_Lambda/TestComponent.codegen.cs

@@ -0,0 +1,37 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+using System.Threading.Tasks;
+
+#line default
+#line hidden
+#line 2 "x:\dir\subdir\Test\TestComponent.cshtml"
+using Microsoft.AspNetCore.Blazor;
+
+#line default
+#line hidden
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static System.Object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            __o = Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>("async (e) => await Task.Delay(10)");
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_Lambda/TestComponent.ir.txt

@@ -0,0 +1,35 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [12] ) - System
+        UsingDirective - (18:2,1 [32] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [17] ) - System.Linq
+        UsingDirective - (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            DesignTimeDirective - 
+                DirectiveToken - (14:0,14 [32] ) - "*, Microsoft.AspNetCore.Blazor"
+                DirectiveToken - (14:0,14 [9] ) - "*, Test"
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning disable 0414
+            CSharpCode - 
+                IntermediateToken -  - CSharp - private static System.Object __o = null;
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning restore 0414
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken -  - CSharp - "async (e) => await Task.Delay(10)"
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+                HtmlContent - (120:2,53 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (120:2,53 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_Lambda/TestComponent.mappings.txt

@@ -0,0 +1,10 @@
+Source Location: (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml)
+|using System.Threading.Tasks|
+Generated Location: (222:9,0 [28] )
+|using System.Threading.Tasks|
+
+Source Location: (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml)
+|using Microsoft.AspNetCore.Blazor|
+Generated Location: (335:14,0 [33] )
+|using Microsoft.AspNetCore.Blazor|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.codegen.cs

@@ -0,0 +1,46 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+using System.Threading.Tasks;
+
+#line default
+#line hidden
+#line 2 "x:\dir\subdir\Test\TestComponent.cshtml"
+using Microsoft.AspNetCore.Blazor;
+
+#line default
+#line hidden
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static System.Object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            __o = Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(OnClick);
+        }
+        #pragma warning restore 1998
+#line 4 "x:\dir\subdir\Test\TestComponent.cshtml"
+            
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+
+#line default
+#line hidden
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.ir.txt

@@ -0,0 +1,37 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [12] ) - System
+        UsingDirective - (18:2,1 [32] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [17] ) - System.Linq
+        UsingDirective - (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            DesignTimeDirective - 
+                DirectiveToken - (14:0,14 [32] ) - "*, Microsoft.AspNetCore.Blazor"
+                DirectiveToken - (14:0,14 [9] ) - "*, Test"
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning disable 0414
+            CSharpCode - 
+                IntermediateToken -  - CSharp - private static System.Object __o = null;
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning restore 0414
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken - (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - OnClick
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+                HtmlContent - (95:2,28 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (95:2,28 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+            CSharpCode - (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml)
+                IntermediateToken - (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    Task OnClick(UIMouseEventArgs e) \n    {\n        return Task.CompletedTask;\n    }\n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.mappings.txt

@@ -0,0 +1,30 @@
+Source Location: (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml)
+|using System.Threading.Tasks|
+Generated Location: (222:9,0 [28] )
+|using System.Threading.Tasks|
+
+Source Location: (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml)
+|using Microsoft.AspNetCore.Blazor|
+Generated Location: (335:14,0 [33] )
+|using Microsoft.AspNetCore.Blazor|
+
+Source Location: (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml)
+|OnClick|
+Generated Location: (1110:31,136 [7] )
+|OnClick|
+
+Source Location: (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+|
+Generated Location: (1233:35,12 [91] )
+|
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_Lambda/TestComponent.codegen.cs

@@ -0,0 +1,37 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+using System.Threading.Tasks;
+
+#line default
+#line hidden
+#line 2 "x:\dir\subdir\Test\TestComponent.cshtml"
+using Microsoft.AspNetCore.Blazor;
+
+#line default
+#line hidden
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static System.Object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            __o = Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>("async (e) => await Task.Delay(10)");
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_Lambda/TestComponent.ir.txt

@@ -0,0 +1,35 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [12] ) - System
+        UsingDirective - (18:2,1 [32] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [17] ) - System.Linq
+        UsingDirective - (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            DesignTimeDirective - 
+                DirectiveToken - (14:0,14 [32] ) - "*, Microsoft.AspNetCore.Blazor"
+                DirectiveToken - (14:0,14 [9] ) - "*, Test"
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning disable 0414
+            CSharpCode - 
+                IntermediateToken -  - CSharp - private static System.Object __o = null;
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning restore 0414
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken -  - CSharp - "async (e) => await Task.Delay(10)"
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+                HtmlContent - (120:2,53 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (120:2,53 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_Lambda/TestComponent.mappings.txt

@@ -0,0 +1,10 @@
+Source Location: (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml)
+|using System.Threading.Tasks|
+Generated Location: (222:9,0 [28] )
+|using System.Threading.Tasks|
+
+Source Location: (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml)
+|using Microsoft.AspNetCore.Blazor|
+Generated Location: (335:14,0 [33] )
+|using Microsoft.AspNetCore.Blazor|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.codegen.cs

@@ -0,0 +1,46 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+#line 1 "x:\dir\subdir\Test\TestComponent.cshtml"
+using System.Threading.Tasks;
+
+#line default
+#line hidden
+#line 2 "x:\dir\subdir\Test\TestComponent.cshtml"
+using Microsoft.AspNetCore.Blazor;
+
+#line default
+#line hidden
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 219
+        private void __RazorDirectiveTokenHelpers__() {
+        }
+        #pragma warning restore 219
+        #pragma warning disable 0414
+        private static System.Object __o = null;
+        #pragma warning restore 0414
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            __o = Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(OnClick);
+        }
+        #pragma warning restore 1998
+#line 4 "x:\dir\subdir\Test\TestComponent.cshtml"
+            
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+
+#line default
+#line hidden
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.ir.txt

@@ -0,0 +1,37 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [12] ) - System
+        UsingDirective - (18:2,1 [32] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [17] ) - System.Linq
+        UsingDirective - (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            DesignTimeDirective - 
+                DirectiveToken - (14:0,14 [32] ) - "*, Microsoft.AspNetCore.Blazor"
+                DirectiveToken - (14:0,14 [9] ) - "*, Test"
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning disable 0414
+            CSharpCode - 
+                IntermediateToken -  - CSharp - private static System.Object __o = null;
+            CSharpCode - 
+                IntermediateToken -  - CSharp - #pragma warning restore 0414
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (29:0,29 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (65:1,34 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken - (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - OnClick
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+                HtmlContent - (95:2,28 [2] x:\dir\subdir\Test\TestComponent.cshtml)
+                    IntermediateToken - (95:2,28 [2] x:\dir\subdir\Test\TestComponent.cshtml) - Html - \n
+            CSharpCode - (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml)
+                IntermediateToken - (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    Task OnClick() \n    {\n        return Task.CompletedTask;\n    }\n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.mappings.txt

@@ -0,0 +1,30 @@
+Source Location: (1:0,1 [28] x:\dir\subdir\Test\TestComponent.cshtml)
+|using System.Threading.Tasks|
+Generated Location: (222:9,0 [28] )
+|using System.Threading.Tasks|
+
+Source Location: (32:1,1 [33] x:\dir\subdir\Test\TestComponent.cshtml)
+|using Microsoft.AspNetCore.Blazor|
+Generated Location: (335:14,0 [33] )
+|using Microsoft.AspNetCore.Blazor|
+
+Source Location: (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml)
+|OnClick|
+Generated Location: (1110:31,136 [7] )
+|OnClick|
+
+Source Location: (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+|
+Generated Location: (1233:35,12 [73] )
+|
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/ChildComponent_WithExplicitEventHandler/TestComponent.codegen.cs

@@ -29,7 +29,7 @@ global::System.Object __typeHelper = "*, TestAssembly";
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
-            __o = new Microsoft.AspNetCore.Blazor.UIEventHandler(
+            __o = new System.Action<Microsoft.AspNetCore.Blazor.UIEventArgs>(
 #line 3 "x:\dir\subdir\Test\TestComponent.cshtml"
                        Increment
 

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/ChildComponent_WithExplicitEventHandler/TestComponent.mappings.txt

@@ -10,7 +10,7 @@ Generated Location: (586:19,38 [15] )
 
 Source Location: (90:2,23 [9] x:\dir\subdir\Test\TestComponent.cshtml)
 |Increment|
-Generated Location: (1154:33,23 [9] )
+Generated Location: (1166:33,23 [9] )
 |Increment|
 
 Source Location: (118:4,12 [100] x:\dir\subdir\Test\TestComponent.cshtml)
@@ -20,7 +20,7 @@ Source Location: (118:4,12 [100] x:\dir\subdir\Test\TestComponent.cshtml)
         counter++;
     }
 |
-Generated Location: (1471:44,12 [100] )
+Generated Location: (1483:44,12 [100] )
 |
     private int counter;
     private void Increment(UIEventArgs e) {

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/ChildComponent_WithLambdaEventHandler/TestComponent.codegen.cs

@@ -24,7 +24,7 @@ global::System.Object __typeHelper = "*, TestAssembly";
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
-            __o = new Microsoft.AspNetCore.Blazor.UIEventHandler(
+            __o = new System.Action<Microsoft.AspNetCore.Blazor.UIEventArgs>(
 #line 2 "x:\dir\subdir\Test\TestComponent.cshtml"
                         (e) => { Increment(); }
 

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/DesignTimeCodeGenerationTest/ChildComponent_WithLambdaEventHandler/TestComponent.mappings.txt

@@ -5,7 +5,7 @@ Generated Location: (468:14,38 [15] )
 
 Source Location: (55:1,24 [23] x:\dir\subdir\Test\TestComponent.cshtml)
 |(e) => { Increment(); }|
-Generated Location: (1037:28,24 [23] )
+Generated Location: (1049:28,24 [23] )
 |(e) => { Increment(); }|
 
 Source Location: (98:3,12 [87] x:\dir\subdir\Test\TestComponent.cshtml)
@@ -15,7 +15,7 @@ Source Location: (98:3,12 [87] x:\dir\subdir\Test\TestComponent.cshtml)
         counter++;
     }
 |
-Generated Location: (1368:39,12 [87] )
+Generated Location: (1380:39,12 [87] )
 |
     private int counter;
     private void Increment() {

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_Lambda/TestComponent.codegen.cs

@@ -0,0 +1,24 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
+    using Microsoft.AspNetCore.Blazor;
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            builder.OpenElement(0, "input");
+            builder.AddAttribute(1, "onclick", Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>("async (e) => await Task.Delay(10)"));
+            builder.CloseElement();
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_Lambda/TestComponent.ir.txt

@@ -0,0 +1,20 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [14] ) - System
+        UsingDirective - (18:2,1 [34] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [19] ) - System.Linq
+        UsingDirective - (1:0,1 [30] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [35] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken -  - CSharp - "async (e) => await Task.Delay(10)"
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.codegen.cs

@@ -0,0 +1,33 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
+    using Microsoft.AspNetCore.Blazor;
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            builder.OpenElement(0, "input");
+            builder.AddAttribute(1, "onclick", Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(OnClick));
+            builder.CloseElement();
+        }
+        #pragma warning restore 1998
+#line 4 "x:\dir\subdir\Test\TestComponent.cshtml"
+            
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+
+#line default
+#line hidden
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.ir.txt

@@ -0,0 +1,22 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [14] ) - System
+        UsingDirective - (18:2,1 [34] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [19] ) - System.Linq
+        UsingDirective - (1:0,1 [30] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [35] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken - (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - OnClick
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+            CSharpCode - (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml)
+                IntermediateToken - (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    Task OnClick(UIMouseEventArgs e) \n    {\n        return Task.CompletedTask;\n    }\n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_ActionEventArgs_MethodGroup/TestComponent.mappings.txt

@@ -0,0 +1,15 @@
+Source Location: (109:3,12 [91] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+|
+Generated Location: (922:22,12 [91] )
+|
+    Task OnClick(UIMouseEventArgs e) 
+    {
+        return Task.CompletedTask;
+    }
+|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_Lambda/TestComponent.codegen.cs

@@ -0,0 +1,24 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
+    using Microsoft.AspNetCore.Blazor;
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            builder.OpenElement(0, "input");
+            builder.AddAttribute(1, "onclick", Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>("async (e) => await Task.Delay(10)"));
+            builder.CloseElement();
+        }
+        #pragma warning restore 1998
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_Lambda/TestComponent.ir.txt

@@ -0,0 +1,20 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [14] ) - System
+        UsingDirective - (18:2,1 [34] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [19] ) - System.Linq
+        UsingDirective - (1:0,1 [30] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [35] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken -  - CSharp - "async (e) => await Task.Delay(10)"
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.codegen.cs

@@ -0,0 +1,33 @@
+// <auto-generated/>
+#pragma warning disable 1591
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
+    using Microsoft.AspNetCore.Blazor;
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+            base.BuildRenderTree(builder);
+            builder.OpenElement(0, "input");
+            builder.AddAttribute(1, "onclick", Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(OnClick));
+            builder.CloseElement();
+        }
+        #pragma warning restore 1998
+#line 4 "x:\dir\subdir\Test\TestComponent.cshtml"
+            
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+
+#line default
+#line hidden
+    }
+}
+#pragma warning restore 1591

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.ir.txt

@@ -0,0 +1,22 @@
+Document - 
+    NamespaceDeclaration -  - Test
+        UsingDirective - (3:1,1 [14] ) - System
+        UsingDirective - (18:2,1 [34] ) - System.Collections.Generic
+        UsingDirective - (53:3,1 [19] ) - System.Linq
+        UsingDirective - (1:0,1 [30] x:\dir\subdir\Test\TestComponent.cshtml) - System.Threading.Tasks
+        UsingDirective - (32:1,1 [35] x:\dir\subdir\Test\TestComponent.cshtml) - Microsoft.AspNetCore.Blazor
+        ClassDeclaration -  - public - TestComponent - Microsoft.AspNetCore.Blazor.Components.BlazorComponent - 
+            MethodDeclaration -  - protected override - void - BuildRenderTree
+                CSharpCode - 
+                    IntermediateToken -  - CSharp - base.BuildRenderTree(builder);
+                HtmlContent - 
+                    IntermediateToken -  - Html - <input 
+                HtmlAttribute -  - =" - "
+                    CSharpExpressionAttributeValue -  - 
+                        IntermediateToken -  - CSharp - Microsoft.AspNetCore.Blazor.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>(
+                        IntermediateToken - (84:2,17 [7] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - OnClick
+                        IntermediateToken -  - CSharp - )
+                HtmlContent - 
+                    IntermediateToken -  - Html - />
+            CSharpCode - (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml)
+                IntermediateToken - (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml) - CSharp - \n    Task OnClick() \n    {\n        return Task.CompletedTask;\n    }\n

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/AsyncEventHandler_OnElement_Action_MethodGroup/TestComponent.mappings.txt

@@ -0,0 +1,15 @@
+Source Location: (109:3,12 [73] x:\dir\subdir\Test\TestComponent.cshtml)
+|
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+|
+Generated Location: (922:22,12 [73] )
+|
+    Task OnClick() 
+    {
+        return Task.CompletedTask;
+    }
+|
+

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/ChildComponent_WithExplicitEventHandler/TestComponent.codegen.cs

@@ -15,7 +15,7 @@ namespace Test
         {
             base.BuildRenderTree(builder);
             builder.OpenComponent<Test.MyComponent>(0);
-            builder.AddAttribute(1, "OnClick", new Microsoft.AspNetCore.Blazor.UIEventHandler(Increment));
+            builder.AddAttribute(1, "OnClick", new System.Action<Microsoft.AspNetCore.Blazor.UIEventArgs>(Increment));
             builder.CloseComponent();
         }
         #pragma warning restore 1998

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/ChildComponent_WithExplicitEventHandler/TestComponent.mappings.txt

@@ -5,7 +5,7 @@ Source Location: (118:4,12 [100] x:\dir\subdir\Test\TestComponent.cshtml)
         counter++;
     }
 |
-Generated Location: (866:22,12 [100] )
+Generated Location: (878:22,12 [100] )
 |
     private int counter;
     private void Increment(UIEventArgs e) {

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/ChildComponent_WithLambdaEventHandler/TestComponent.codegen.cs

@@ -14,7 +14,7 @@ namespace Test
         {
             base.BuildRenderTree(builder);
             builder.OpenComponent<Test.MyComponent>(0);
-            builder.AddAttribute(1, "OnClick", new Microsoft.AspNetCore.Blazor.UIEventHandler(e => { Increment(); }));
+            builder.AddAttribute(1, "OnClick", new System.Action<Microsoft.AspNetCore.Blazor.UIEventArgs>(e => { Increment(); }));
             builder.CloseComponent();
         }
         #pragma warning restore 1998

test/Microsoft.AspNetCore.Blazor.Build.Test/TestFiles/RuntimeCodeGenerationTest/ChildComponent_WithLambdaEventHandler/TestComponent.mappings.txt

@@ -5,7 +5,7 @@ Source Location: (96:3,12 [87] x:\dir\subdir\Test\TestComponent.cshtml)
         counter++;
     }
 |
-Generated Location: (838:21,12 [87] )
+Generated Location: (850:21,12 [87] )
 |
     private int counter;
     private void Increment() {

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/ComponentRenderingTest.cs

@@ -63,6 +63,23 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Assert.Equal("Current count: 1", countDisplayElement.Text);
         }
 
+        [Fact]
+        public void CanTriggerAsyncEventHandlers()
+        {
+            // Initial state is stopped
+            var appElement = MountTestComponent<AsyncEventHandlerComponent>();
+            var stateElement = appElement.FindElement(By.Id("state"));
+            Assert.Equal("Stopped", stateElement.Text);
+
+            // Clicking 'tick' changes the state, and starts a task
+            appElement.FindElement(By.Id("tick")).Click();
+            Assert.Equal("Started", stateElement.Text);
+
+            // Clicking 'tock' completes the task, which updates the state
+            appElement.FindElement(By.Id("tock")).Click();
+            Assert.Equal("Stopped", stateElement.Text);
+        }
+
         [Fact]
         public void CanTriggerKeyPressEvents()
         {

test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test/BaseTagHelperDescriptorProviderTest.cs

@@ -26,10 +26,19 @@ namespace Microsoft.AspNetCore.Blazor.Razor.Extensions
                 Array.Empty<SyntaxTree>(),
                 metadataReferences,
                 new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+
+            CSharpParseOptions = new CSharpParseOptions(LanguageVersion.CSharp7_3);
         }
 
         protected static Compilation BaseCompilation { get; }
 
+        protected static CSharpParseOptions CSharpParseOptions { get; }
+
+        protected static CSharpSyntaxTree Parse(string text)
+        {
+            return (CSharpSyntaxTree)CSharpSyntaxTree.ParseText(text, CSharpParseOptions);
+        }
+
         // For simplicity in testing, exclude the built-in components. We'll add more and we
         // don't want to update the tests when that happens.
         protected static TagHelperDescriptor[] ExcludeBuiltInComponents(TagHelperDescriptorProviderContext context)

test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test/BindTagHelperDescriptorProviderTest.cs

@@ -15,7 +15,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor.Extensions
         public void Excecute_FindsBindTagHelperOnComponentType_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -128,7 +128,7 @@ namespace Test
         public void Excecute_NoMatchedPropertiesOnComponent_IgnoresComponent()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -170,7 +170,7 @@ namespace Test
         public void Excecute_BindOnElement_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -303,7 +303,7 @@ namespace Test
         public void Execute_BindOnElementWithSuffix_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -357,7 +357,7 @@ namespace Test
         public void Execute_BindOnInputElementWithoutTypeAttribute_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -412,7 +412,7 @@ namespace Test
         public void Execute_BindOnInputElementWithTypeAttribute_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -479,7 +479,7 @@ namespace Test
         public void Execute_BindOnInputElementWithTypeAttributeAndSuffix_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test

test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test/ComponentTagHelperDescriptorProviderTest.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor.Extensions
         {
             // Arrange
 
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -129,7 +129,7 @@ namespace Test
         {
             // Arrange
 
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -169,7 +169,7 @@ namespace Test
         {
             // Arrange
 
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -214,7 +214,7 @@ namespace Test
         {
             // Arrange
 
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using Microsoft.AspNetCore.Blazor.Components;
 
 namespace Test
@@ -265,7 +265,8 @@ namespace Test
         {
             // Arrange
 
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
+using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;
 
@@ -273,7 +274,7 @@ namespace Test
 {
     public class MyComponent : BlazorComponent
     {
-        public UIEventHandler OnClick { get; set; }
+        public Action<UIMouseEventArgs> OnClick { get; set; }
     }
 }
 
@@ -298,7 +299,7 @@ namespace Test
 
             var attribute = Assert.Single(component.BoundAttributes);
             Assert.Equal("OnClick", attribute.Name);
-            Assert.Equal(BlazorApi.UIEventHandler.FullTypeName, attribute.TypeName);
+            Assert.Equal("System.Action<Microsoft.AspNetCore.Blazor.UIMouseEventArgs>", attribute.TypeName);
 
             Assert.False(attribute.HasIndexer);
             Assert.False(attribute.IsBooleanProperty);

test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test/EventHandlerTagHelperDescriptorProviderTest.cs

@@ -15,7 +15,7 @@ namespace Microsoft.AspNetCore.Blazor.Razor.Extensions
         public void Excecute_EventHandler_CreatesDescriptor()
         {
             // Arrange
-            var compilation = BaseCompilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(@"
+            var compilation = BaseCompilation.AddSyntaxTrees(Parse(@"
 using System;
 using Microsoft.AspNetCore.Blazor;
 using Microsoft.AspNetCore.Blazor.Components;

test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test/Microsoft.AspNetCore.Blazor.Razor.Extensions.Test.csproj

@@ -17,7 +17,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.6.1" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.8.0-beta3" />
     <PackageReference Include="Microsoft.Extensions.DependencyModel" Version="2.0.4" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
     <PackageReference Include="xunit" Version="2.3.1" />

test/Microsoft.AspNetCore.Blazor.Test/RenderTreeBuilderTest.cs

@@ -168,7 +168,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
         {
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
-            UIEventHandler eventHandler = eventInfo => { };
+            Action<UIEventArgs> eventHandler = eventInfo => { };
 
             // Act
             builder.OpenElement(0, "myelement");                    //  0: <myelement
@@ -498,12 +498,12 @@ namespace Microsoft.AspNetCore.Blazor.Test
         }
 
         [Fact]
-        public void AddAttribute_Element_UIEventHandler_AddsFrame()
+        public void AddAttribute_Element_EventHandler_AddsFrame()
         {
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
 
-            var value = new UIEventHandler((e) => { });
+            var value = new Action<UIEventArgs>((e) => { });
 
             // Act
             builder.OpenElement(0, "elem");
@@ -518,14 +518,14 @@ namespace Microsoft.AspNetCore.Blazor.Test
         }
 
         [Fact]
-        public void AddAttribute_Element_NullUIEventHandler_IgnoresFrame()
+        public void AddAttribute_Element_NullEventHandler_IgnoresFrame()
         {
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
 
             // Act
             builder.OpenElement(0, "elem");
-            builder.AddAttribute(1, "attr", (UIEventHandler)null);
+            builder.AddAttribute(1, "attr", (Action<UIEventArgs>)null);
             builder.CloseElement();
 
             // Assert
@@ -571,15 +571,15 @@ namespace Microsoft.AspNetCore.Blazor.Test
                 frame => AssertFrame.Element(frame, "elem", 1, 0));
         }
 
-        public static TheoryData<UIEventHandler> UIEventHandlerValues => new TheoryData<UIEventHandler>
+        public static TheoryData<Action<UIEventArgs>> EventHandlerValues => new TheoryData<Action<UIEventArgs>>
         {
             null,
             (e) => { },
         };
 
         [Theory]
-        [MemberData(nameof(UIEventHandlerValues))]
-        public void AddAttribute_Component_EventHandlerValue_SetsAttributeValue(UIEventHandler value)
+        [MemberData(nameof(EventHandlerValues))]
+        public void AddAttribute_Component_EventHandlerValue_SetsAttributeValue(Action<UIEventArgs> value)
         {
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
@@ -688,12 +688,12 @@ namespace Microsoft.AspNetCore.Blazor.Test
         }
 
         [Fact]
-        public void AddAttribute_Element_ObjectUIEventHandler_AddsFrame()
+        public void AddAttribute_Element_ObjectEventHandler_AddsFrame()
         {
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
 
-            var value = new UIEventHandler((e) => { });
+            var value = new Action<UIEventArgs>((e) => { });
 
             // Act
             builder.OpenElement(0, "elem");
@@ -713,7 +713,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
             // Arrange
             var builder = new RenderTreeBuilder(new TestRenderer());
 
-            var value = new UIEventHandler((e) => { });
+            var value = new Action<UIEventArgs>((e) => { });
 
             // Act
             builder.OpenComponent<TestComponent>(0);

test/Microsoft.AspNetCore.Blazor.Test/RenderTreeDiffBuilderTest.cs

@@ -421,9 +421,9 @@ namespace Microsoft.AspNetCore.Blazor.Test
         public void RecognizesAttributeEventHandlerValuesChanged()
         {
             // Arrange
-            UIEventHandler retainedHandler = _ => { };
-            UIEventHandler removedHandler = _ => { };
-            UIEventHandler addedHandler = _ => { };
+            Action<UIEventArgs> retainedHandler = _ => { };
+            Action<UIEventArgs> removedHandler = _ => { };
+            Action<UIEventArgs> addedHandler = _ => { };
             oldTree.OpenElement(0, "My element");
             oldTree.AddAttribute(1, "onfoo", retainedHandler);
             oldTree.AddAttribute(2, "onbar", removedHandler);
@@ -1159,7 +1159,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
         public void PreservesEventHandlerIdsForRetainedEventHandlers()
         {
             // Arrange
-            UIEventHandler retainedHandler = _ => { };
+            Action<UIEventArgs> retainedHandler = _ => { };
             oldTree.OpenElement(0, "My element");
             oldTree.AddAttribute(1, "ontest", retainedHandler);
             oldTree.CloseElement();
@@ -1185,7 +1185,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
         public void PreservesEventHandlerIdsForRetainedEventHandlers_SlowPath()
         {
             // Arrange
-            UIEventHandler retainedHandler = _ => { };
+            Action<UIEventArgs> retainedHandler = _ => { };
             oldTree.OpenElement(0, "My element");
             oldTree.AddAttribute(0, "ontest", retainedHandler);
             oldTree.CloseElement();

test/Microsoft.AspNetCore.Blazor.Test/RendererTest.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Blazor.Components;
 using Microsoft.AspNetCore.Blazor.Rendering;
 using Microsoft.AspNetCore.Blazor.RenderTree;
@@ -289,7 +290,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
         {
             // Arrange: Render a component with an event handler
             var renderer = new TestRenderer();
-            UIEventHandler handler = args => throw new NotImplementedException();
+            Action<UIEventArgs> handler = args => throw new NotImplementedException();
             var component = new TestComponent(builder =>
             {
                 builder.OpenElement(0, "mybutton");
@@ -531,7 +532,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
             // Arrange
             var renderer = new TestRenderer();
             var eventCount = 0;
-            UIEventHandler origEventHandler = args => { eventCount++; };
+            Action<UIEventArgs> origEventHandler = args => { eventCount++; };
             var component = new EventComponent { OnTest = origEventHandler };
             var componentId = renderer.AssignComponentId(component);
             component.TriggerRender();
@@ -568,7 +569,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
             // Arrange
             var renderer = new TestRenderer();
             var eventCount = 0;
-            UIEventHandler origEventHandler = args => { eventCount++; };
+            Action<UIEventArgs> origEventHandler = args => { eventCount++; };
             var component = new EventComponent { OnTest = origEventHandler };
             var componentId = renderer.AssignComponentId(component);
             component.TriggerRender();
@@ -601,7 +602,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
             // Arrange
             var renderer = new TestRenderer();
             var eventCount = 0;
-            UIEventHandler origEventHandler = args => { eventCount++; };
+            Action<UIEventArgs> origEventHandler = args => { eventCount++; };
             var component = new ConditionalParentComponent<EventComponent>
             {
                 IncludeChild = true,
@@ -650,7 +651,7 @@ namespace Microsoft.AspNetCore.Blazor.Test
             // Arrange
             var renderer = new TestRenderer();
             var eventCount = 0;
-            UIEventHandler origEventHandler = args => { eventCount++; };
+            Action<UIEventArgs> origEventHandler = args => { eventCount++; };
             var component = new EventComponent { OnTest = origEventHandler };
             var componentId = renderer.AssignComponentId(component);
             component.TriggerRender();
@@ -1011,8 +1012,8 @@ namespace Microsoft.AspNetCore.Blazor.Test
 
         private class EventComponent : AutoRenderComponent, IComponent, IHandleEvent
         {
-            public UIEventHandler OnTest { get; set; }
-            public UIMouseEventHandler OnClick { get; set; }
+            public Action<UIEventArgs> OnTest { get; set; }
+            public Action<UIMouseEventArgs> OnClick { get; set; }
             public Action OnClickAction { get; set; }
 
             public bool SkipElement { get; set; }
@@ -1044,8 +1045,10 @@ namespace Microsoft.AspNetCore.Blazor.Test
                 builder.AddContent(6, $"Render count: {++renderCount}");
             }
 
-            public void HandleEvent(UIEventHandler handler, UIEventArgs args)
-                => handler(args);
+            public void HandleEvent(EventHandlerInvoker binding, UIEventArgs args)
+            {
+                binding.Invoke(args);
+            }
         }
 
         private class ConditionalParentComponent<T> : AutoRenderComponent where T : IComponent
@@ -1105,9 +1108,9 @@ namespace Microsoft.AspNetCore.Blazor.Test
                 Render();
             }
 
-            public void HandleEvent(UIEventHandler handler, UIEventArgs args)
+            public void HandleEvent(EventHandlerInvoker binding, UIEventArgs args)
             {
-                handler(args);
+                var task = binding.Invoke(args);
                 Render();
             }
 
@@ -1149,9 +1152,9 @@ namespace Microsoft.AspNetCore.Blazor.Test
             public bool CheckboxEnabled;
             public string SomeStringProperty;
 
-            public void HandleEvent(UIEventHandler handler, UIEventArgs args)
+            public void HandleEvent(EventHandlerInvoker binding, UIEventArgs args)
             {
-                handler(args);
+                binding.Invoke(args);
                 TriggerRender();
             }
 

test/shared/AssertFrame.cs

@@ -47,7 +47,7 @@ namespace Microsoft.AspNetCore.Blazor.Test.Helpers
             Assert.Equal(attributeValue, frame.AttributeValue);
         }
 
-        public static void Attribute(RenderTreeFrame frame, string attributeName, UIEventHandler attributeEventHandlerValue, int? sequence = null)
+        public static void Attribute(RenderTreeFrame frame, string attributeName, Action<UIEventArgs> attributeEventHandlerValue, int? sequence = null)
         {
             AssertFrame.Attribute(frame, attributeName, sequence);
             Assert.Equal(attributeEventHandlerValue, frame.AttributeValue);

test/testapps/BasicTestApp/AsyncEventHandlerComponent.cshtml

@@ -0,0 +1,35 @@
+@using System.Threading.Tasks
+@using Microsoft.AspNetCore.Blazor
+
+<div>
+    <span id="state">@state</span>
+    <button id="tick" onclick="@Tick">Tick</button>
+    <button id="tock" onclick="@Tock">Tock</button>
+</div>
+
+@functions
+{
+    TaskCompletionSource<object> _tcs;
+    string state = "Stopped";
+    Task Tick(UIMouseEventArgs e)
+    {
+        if (_tcs == null)
+        {
+            _tcs = new TaskCompletionSource<object>();
+
+            state = "Started";
+            return _tcs.Task.ContinueWith((task) =>
+            {
+                state = "Stopped";
+                _tcs = null;
+            });
+        }
+
+        return Task.CompletedTask;
+    }
+
+    void Tock(UIMouseEventArgs e)
+    {
+        _tcs.TrySetResult(null);
+    }
+}

test/testapps/BasicTestApp/BasicTestApp.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk.Web">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>

test/testapps/BasicTestApp/wwwroot/index.html

@@ -10,6 +10,7 @@
     Select test:
     <select onchange="mountTestComponent(event.target.value)">
       <option value="">Choose...</option>
+      <option value="BasicTestApp.AsyncEventHandlerComponent">Async event handlers</option>
       <option value="BasicTestApp.AddRemoveChildComponents">Add/remove child components</option>
       <option value="BasicTestApp.CounterComponent">Counter</option>
       <option value="BasicTestApp.CounterComponentUsingChild">Counter using child component</option>