[X] binding find the right indexer (#7896)

supports having multiple indexers on a bound source, try to invoke the right one

- fixes #7837

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -495,7 +495,22 @@ namespace Xamarin.Forms.Build.Tasks
 				if (indexArg != null) {
 					var defaultMemberAttribute = previousPartTypeRef.GetCustomAttribute(module, ("mscorlib", "System.Reflection", "DefaultMemberAttribute"));
 					var indexerName = defaultMemberAttribute?.ConstructorArguments?.FirstOrDefault().Value as string ?? "Item";
-					var indexer = previousPartTypeRef.GetProperty(pd => pd.Name == indexerName && pd.GetMethod != null && pd.GetMethod.IsPublic, out var indexerDeclTypeRef);
+					PropertyDefinition indexer = null;
+					TypeReference indexerDeclTypeRef = null;
+					if (int.TryParse(indexArg, out _))
+						indexer = previousPartTypeRef.GetProperty(pd => pd.Name == indexerName
+																	 && pd.GetMethod != null
+																	 && TypeRefComparer.Default.Equals(pd.GetMethod.Parameters[0].ParameterType, module.ImportReference(("mscorlib", "System", "Int32")))
+																	 && pd.GetMethod.IsPublic, out indexerDeclTypeRef);
+					indexer = indexer ?? previousPartTypeRef.GetProperty(pd => pd.Name == indexerName
+																			&& pd.GetMethod != null
+																			&& TypeRefComparer.Default.Equals(pd.GetMethod.Parameters[0].ParameterType, module.ImportReference(("mscorlib", "System", "String")))
+																			&& pd.GetMethod.IsPublic, out indexerDeclTypeRef);
+					indexer = indexer ?? previousPartTypeRef.GetProperty(pd => pd.Name == indexerName
+																			&& pd.GetMethod != null
+																			&& TypeRefComparer.Default.Equals(pd.GetMethod.Parameters[0].ParameterType, module.ImportReference(("mscorlib", "System", "String")))
+																			&& pd.GetMethod.IsPublic, out indexerDeclTypeRef);
+
 					properties.Add((indexer, indexerDeclTypeRef, indexArg));
 					var indexType = indexer.GetMethod.Parameters[0].ParameterType.ResolveGenericParameters(indexerDeclTypeRef);
 					if (!TypeRefComparer.Default.Equals(indexType, module.TypeSystem.String) && !TypeRefComparer.Default.Equals(indexType, module.TypeSystem.Int32))

Xamarin.Forms.Build.Tasks/TypeReferenceExtensions.cs

@@ -11,11 +11,9 @@ namespace Xamarin.Forms.Build.Tasks
 	{
 		static string GetAssembly(TypeReference typeRef)
 		{
-			var md = typeRef.Scope as ModuleDefinition;
-			if (md != null)
+			if (typeRef.Scope is ModuleDefinition md)
 				return md.Assembly.FullName;
-			var anr = typeRef.Scope as AssemblyNameReference;
-			if (anr != null)
+			if (typeRef.Scope is AssemblyNameReference anr)
 				return anr.FullName;
 			throw new ArgumentOutOfRangeException(nameof(typeRef));
 		}

Xamarin.Forms.Core/BindingExpression.cs

@@ -243,6 +243,54 @@ namespace Xamarin.Forms
 			}
 		}
 
+		PropertyInfo GetIndexer(TypeInfo sourceType, string indexerName, string content)
+		{
+			if (int.TryParse(content, out _)) { //try to find an indexer taking an int
+				foreach (var pi in sourceType.DeclaredProperties) {
+					if (pi.Name != indexerName)
+						continue;
+					if (pi.CanRead && pi.GetMethod.GetParameters()[0].ParameterType == typeof(int))
+						return pi;
+					if (pi.CanWrite && pi.SetMethod.ReturnType == typeof(int))
+						return pi;
+				}
+			}
+
+		
+			//property isn't an int, or there wasn't any int indexer
+			foreach (var pi in sourceType.DeclaredProperties) {
+				if (pi.Name != indexerName)
+					continue;
+				if (pi.CanRead && pi.GetMethod.GetParameters()[0].ParameterType == typeof(string))
+					return pi;
+				if (pi.CanWrite && pi.SetMethod.ReturnType == typeof(string))
+					return pi;
+			}
+
+			//try to fallback to an object indexer
+			foreach (var pi in sourceType.DeclaredProperties)
+			{
+				if (pi.Name != indexerName)
+					continue;
+				if (pi.CanRead && pi.GetMethod.GetParameters()[0].ParameterType == typeof(object))
+					return pi;
+				if (pi.CanWrite && pi.SetMethod.ReturnType == typeof(object))
+					return pi;
+			}
+
+			//defined on an interface ?
+			foreach (var face in sourceType.ImplementedInterfaces) {
+				if (GetIndexer(face.GetTypeInfo(), indexerName, content) is PropertyInfo pi)
+					return pi;
+			}
+
+			//defined on a base class ?
+			if (sourceType.BaseType is Type baseT && GetIndexer(baseT.GetTypeInfo(), indexerName, content) is PropertyInfo p)
+				return p;
+			return null;
+		}
+
+
 		void SetupPart(TypeInfo sourceType, BindingExpressionPart part)
 		{
 			part.Arguments = null;
@@ -254,8 +302,7 @@ namespace Xamarin.Forms
 			{
 				if (sourceType.IsArray)
 				{
-					int index;
-					if (!int.TryParse(part.Content, out index))
+					if (!int.TryParse(part.Content, out var index))
 						Log.Warning("Binding", "{0} could not be parsed as an index for a {1}", part.Content, sourceType);
 					else
 						part.Arguments = new object[] { index };
@@ -265,46 +312,16 @@ namespace Xamarin.Forms
 					part.SetterType = sourceType.GetElementType();
 				}
 
-				DefaultMemberAttribute defaultMember = null;
-				foreach (var attrib in sourceType.GetCustomAttributes(typeof(DefaultMemberAttribute), true))
+				string indexerName = "Item";
+				foreach (DefaultMemberAttribute attrib in sourceType.GetCustomAttributes(typeof(DefaultMemberAttribute), true))
 				{
-					if (attrib is DefaultMemberAttribute d)
-					{
-						defaultMember = d;
-						break;
-					}
+					indexerName = attrib.MemberName;
+					break;
 				}
 
-				string indexerName = defaultMember != null ? defaultMember.MemberName : "Item";
-
 				part.IndexerName = indexerName;
 
-#if NETSTANDARD2_0
-				try {
-					property = sourceType.GetDeclaredProperty(indexerName);
-				}
-				catch (AmbiguousMatchException) {
-					// Get most derived instance of property
-					foreach (var p in sourceType.GetProperties()) {
-						if (p.Name == indexerName && (property == null || property.DeclaringType.IsAssignableFrom(property.DeclaringType)))
-							property = p;
-					}
-				}
-#else
-				property = sourceType.GetDeclaredProperty(indexerName);
-#endif
-
-				if (property == null) //is the indexer defined on the base class?
-					property = sourceType.BaseType.GetProperty(indexerName);
-				if (property == null) //is the indexer defined on implemented interface ?
-				{
-					foreach (var implementedInterface in sourceType.ImplementedInterfaces)
-					{
-						property = implementedInterface.GetProperty(indexerName);
-						if (property != null)
-							break;
-					}
-				}
+				property = GetIndexer(sourceType, indexerName, part.Content);
 
 				if (property != null)
 				{
@@ -312,9 +329,7 @@ namespace Xamarin.Forms
 					ParameterInfo[] array = property.GetIndexParameters();
 
 					if (array.Length > 0)
-					{
 						parameter = array[0];
-					}
 
 					if (parameter != null)
 					{

Xamarin.Forms.Xaml.UnitTests/Issues/Gh7837.xaml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+        xmlns="http://xamarin.com/schemas/2014/forms"
+        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+        xmlns:local="using:Xamarin.Forms.Xaml.UnitTests"
+        x:Class="Xamarin.Forms.Xaml.UnitTests.Gh7837">
+    <ContentPage.BindingContext>
+        <local:Gh7837VM />
+    </ContentPage.BindingContext>
+    <StackLayout>
+        <Label x:Name="label0" Text="{Binding .[42]}" />
+        <Label x:Name="label1" Text="{Binding .[foo]}" />
+        <Label x:Name="label2" Text="{Binding .[42]}" x:DataType="local:Gh7837VM" />
+        <Label x:Name="label3" Text="{Binding .[foo]}" x:DataType="local:Gh7837VM" />
+    </StackLayout>
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh7837.xaml.cs

@@ -0,0 +1,50 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms;
+using Xamarin.Forms.Core.UnitTests;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	public class Gh7837VMBase //using a base class to test #2131
+	{
+		public string this[int index] => "";
+		public string this[string index] => "";
+	}
+
+	public class Gh7837VM : Gh7837VMBase
+	{
+		public new string this[int index] => index == 42 ? "forty-two" : "dull number";
+		public new string this[string index] => index.ToUpper();
+	}
+
+	public partial class Gh7837 : ContentPage
+	{
+		public Gh7837() => InitializeComponent();
+		public Gh7837(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		[TestFixture]
+		class Tests
+		{
+			[SetUp] public void Setup() => Device.PlatformServices = new MockPlatformServices();
+			[TearDown] public void TearDown() => Device.PlatformServices = null;
+
+			[Test]
+			public void BindingWithMultipleIndexers([Values(false, true)]bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					MockCompiler.Compile(typeof(Gh7837));
+				var layout = new Gh7837(useCompiledXaml);
+				Assert.That(layout.label0.Text, Is.EqualTo("forty-two"));
+				Assert.That(layout.label1.Text, Is.EqualTo("FOO"));
+				Assert.That(layout.label2.Text, Is.EqualTo("forty-two"));
+				Assert.That(layout.label3.Text, Is.EqualTo("FOO"));
+			}
+		}
+	}
+}

Xamarin.Forms.Xaml.UnitTests/MockCompiler.cs

@@ -35,8 +35,7 @@ namespace Xamarin.Forms.Xaml.UnitTests
 				BuildEngine = new MSBuild.UnitTests.DummyBuildEngine()
 			};
 
-			IList<Exception> exceptions;
-			if (xamlc.Execute(out exceptions) || exceptions == null || !exceptions.Any()) {
+			if (xamlc.Execute(out IList<Exception> exceptions) || exceptions == null || !exceptions.Any()) {
 				methdoDefinition = xamlc.InitCompForType;
 				return;
 			}