[UWP] Allow embedding Forms page in secondary window (#5658)

* Make secondary window work in UWP (fixes #2229)

* Update Xamarin.Forms.Core/Internals/Ticker.cs

Co-Authored-By: hartez <hartez@users.noreply.github.com>

Xamarin.Forms.ControlGallery.WindowsUniversal/SecondaryWindowService.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Threading.Tasks;
+using Windows.ApplicationModel.Core;
+using Windows.UI.Core;
+using Windows.UI.ViewManagement;
+using Windows.UI.Xaml;
+using Xamarin.Forms;
+using Xamarin.Forms.ControlGallery.WindowsUniversal;
+using Xamarin.Forms.Controls;
+using Xamarin.Forms.Platform.UWP;
+
+[assembly: Dependency(typeof(SecondaryWindowService))]
+namespace Xamarin.Forms.ControlGallery.WindowsUniversal
+{
+	class SecondaryWindowService : ISecondaryWindowService
+	{
+		public async Task OpenSecondaryWindow(Type pageType)
+		{
+			CoreApplicationView newView = CoreApplication.CreateNewView();
+			int newViewId = 0;
+			await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
+			{
+				var frame = new Windows.UI.Xaml.Controls.Frame();
+				frame.Navigate(pageType);
+				Window.Current.Content = frame;
+				Window.Current.Activate();
+
+				newViewId = ApplicationView.GetForCurrentView().Id;
+			});
+			bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
+		}
+
+		public async Task OpenSecondaryWindow(ContentPage page)
+		{
+			CoreApplicationView newView = CoreApplication.CreateNewView();
+			int newViewId = 0;
+			await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
+			{
+				var frame = new Windows.UI.Xaml.Controls.Frame();
+				frame.Navigate(page);
+				Window.Current.Content = frame;
+				Window.Current.Activate();
+
+				newViewId = ApplicationView.GetForCurrentView().Id;
+			});
+			bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
+		}
+	}
+}

Xamarin.Forms.ControlGallery.WindowsUniversal/Xamarin.Forms.ControlGallery.WindowsUniversal.csproj

@@ -124,6 +124,7 @@
     <Compile Include="PlatformSpecificCoreGalleryFactory.cs" />
     <Compile Include="RegistrarValidationService.cs" />
     <Compile Include="SampleNativeControl.cs" />
+    <Compile Include="SecondaryWindowService.cs" />
     <Compile Include="_2489CustomRenderer.cs" />
     <Compile Include="_57114Renderer.cs" />
     <Compile Include="_58406EffectRenderer.cs" />

Xamarin.Forms.Controls/CoreGallery.cs

@@ -10,6 +10,8 @@ using Xamarin.Forms.PlatformConfiguration;
 using Xamarin.Forms.PlatformConfiguration.AndroidSpecific;
 using Xamarin.Forms.PlatformConfiguration.iOSSpecific;
 using Xamarin.Forms.Controls.GalleryPages.VisualStateManagerGalleries;
+using Xamarin.Forms.Controls.Issues;
+
 namespace Xamarin.Forms.Controls
 {
 	[Preserve(AllMembers = true)]
@@ -562,6 +564,14 @@ namespace Xamarin.Forms.Controls
 				}
 			};
 
+			var secondaryWindowService = DependencyService.Get<ISecondaryWindowService>();
+			if (secondaryWindowService != null)
+			{
+				var openSecondWindowButton = new Button() { Text = "Open Secondary Window" };
+				openSecondWindowButton.Clicked += (obj, args) => { secondaryWindowService.OpenSecondaryWindow(new Issue2482()); };
+				stackLayout.Children.Add(openSecondWindowButton);
+			}
+
 			this.SetAutomationPropertiesName("Gallery");
 			this.SetAutomationPropertiesHelpText("Lists all gallery pages");
 

Xamarin.Forms.Controls/ISecondaryWindowService.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Xamarin.Forms.Controls
+{
+	public interface ISecondaryWindowService
+	{
+		Task OpenSecondaryWindow(Type pageType);
+		Task OpenSecondaryWindow(ContentPage page);
+	}
+}

Xamarin.Forms.Core/Internals/Ticker.cs

@@ -42,7 +42,22 @@ namespace Xamarin.Forms.Internals
 		public static Ticker Default
 		{
 			internal set { s_ticker = value; }
-			get { return s_ticker ?? (s_ticker =  Device.PlatformServices.CreateTicker()); }
+			get
+			{
+				if (s_ticker == null)
+				{
+					s_ticker = Device.PlatformServices.CreateTicker();
+				}
+
+				return s_ticker.GetTickerInstance(); 
+			}
+		}
+
+		protected virtual Ticker GetTickerInstance()
+		{
+			// This method is provided so platforms can override it and return something other than
+			// the normal Ticker singleton
+			return s_ticker;
 		}
 
 		public virtual int Insert(Func<long, bool> timeout)

Xamarin.Forms.Platform.UAP/Forms.cs

@@ -83,7 +83,7 @@ namespace Xamarin.Forms
 			return FlowDirection.MatchParent;
 		}
 
-		static Windows.UI.Xaml.ResourceDictionary GetTabletResources()
+		internal static Windows.UI.Xaml.ResourceDictionary GetTabletResources()
 		{
 			return new Windows.UI.Xaml.ResourceDictionary {
 				Source = new Uri("ms-appx:///Xamarin.Forms.Platform.UAP/Resources.xbf")

Xamarin.Forms.Platform.UAP/Platform.cs

@@ -67,9 +67,16 @@ namespace Xamarin.Forms.Platform.UWP
 
 			_page = page;
 
+			var current = Windows.UI.Xaml.Application.Current;
+
+			if (!current.Resources.ContainsKey("RootContainerStyle"))
+			{
+				Windows.UI.Xaml.Application.Current.Resources.MergedDictionaries.Add(Forms.GetTabletResources());
+			}
+
 			_container = new Canvas
 			{
-				Style = (Windows.UI.Xaml.Style)Windows.UI.Xaml.Application.Current.Resources["RootContainerStyle"]
+				Style = (Windows.UI.Xaml.Style)current.Resources["RootContainerStyle"]
 			};
 
 			_page.Content = _container;

Xamarin.Forms.Platform.UAP/WindowsBasePlatformServices.cs

@@ -26,19 +26,24 @@ namespace Xamarin.Forms.Platform.UWP
 {
 	internal abstract class WindowsBasePlatformServices : IPlatformServices
 	{
+		const string WrongThreadError = "RPC_E_WRONG_THREAD";
 		readonly CoreDispatcher _dispatcher;
 
 		protected WindowsBasePlatformServices(CoreDispatcher dispatcher)
 		{
-			if (dispatcher == null)
-				throw new ArgumentNullException(nameof(dispatcher));
-
-			_dispatcher = dispatcher;
+			_dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
 		}
 
-		public void BeginInvokeOnMainThread(Action action)
+		public async void BeginInvokeOnMainThread(Action action)
 		{
+			if (CoreApplication.Views.Count == 1)
+			{
+				// This is the normal scenario - one window only
 				_dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => action()).WatchForError();
+				return;
+			}
+
+			await TryAllDispatchers(action);
 		}
 
 		public Ticker CreateTicker()
@@ -115,7 +120,23 @@ namespace Xamarin.Forms.Platform.UWP
 			return new WindowsIsolatedStorage(ApplicationData.Current.LocalFolder);
 		}
 
-		public bool IsInvokeRequired => !_dispatcher.HasThreadAccess;
+		public bool IsInvokeRequired
+		{
+			get
+			{
+				if (CoreApplication.Views.Count == 1)
+				{
+					return !_dispatcher.HasThreadAccess;
+				}
+
+				if (Window.Current?.Dispatcher != null)
+				{
+					return !Window.Current.Dispatcher.HasThreadAccess;
+				}
+
+				return true;
+			}
+		}
 
 		public string RuntimePlatform => Device.UWP;
 
@@ -152,5 +173,90 @@ namespace Xamarin.Forms.Platform.UWP
 		{
 			return Platform.GetNativeSize(view, widthConstraint, heightConstraint);
 		}
+
+		async Task TryAllDispatchers(Action action)
+		{
+			// Our best bet is Window.Current; most of the time, that's the Dispatcher we need
+			var currentWindow = Window.Current;
+
+			if (currentWindow?.Dispatcher != null)
+			{
+				try
+				{
+					await TryDispatch(currentWindow.Dispatcher, action);
+					return;
+				}
+				catch (Exception ex) when (ex.Message.Contains(WrongThreadError))
+				{
+					// The current window is not the one we need 
+				}
+			}
+
+			// Either Window.Current was the wrong Dispatcher, or Window.Current was null because we're on a 
+			// non-UI thread (e.g., one from the thread pool). So now it's time to try all the available Dispatchers 
+
+			var views = CoreApplication.Views;
+
+			for (int n = 0; n < views.Count; n++)
+			{
+				var dispatcher = views[n].Dispatcher;
+
+				if (dispatcher == null || dispatcher == currentWindow?.Dispatcher)
+				{
+					// Obviously null Dispatchers are no good, and we already tried the one from currentWindow
+					continue;
+				}
+
+				// We need to ignore Deactivated/Never Activated windows, but it's possible we can't access their 
+				// properties from this thread. So we'll check those using the Dispatcher
+				bool activated = false;
+
+				await TryDispatch(dispatcher, () => {
+					var mode = views[n].CoreWindow.ActivationMode;
+					activated = (mode == CoreWindowActivationMode.ActivatedInForeground
+						|| mode == CoreWindowActivationMode.ActivatedNotForeground);
+				});
+
+				if (!activated)
+				{
+					// This is a deactivated (or not yet activated) window; move on
+					continue;
+				}
+
+				try
+				{
+					await TryDispatch(dispatcher, action);
+					return;
+				}
+				catch (Exception ex) when (ex.Message.Contains(WrongThreadError))
+				{
+					// This was the incorrect dispatcher; move on to try another one
+				}
+			}
+		}
+
+		async Task<bool> TryDispatch(CoreDispatcher dispatcher, Action action)
+		{
+			if (dispatcher == null)
+			{
+				throw new ArgumentNullException(nameof(dispatcher));
+			}
+
+			var taskCompletionSource = new TaskCompletionSource<bool>();
+
+			await dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => {
+				try
+				{
+					action();
+					taskCompletionSource.SetResult(true);
+				}
+				catch (Exception ex)
+				{
+					taskCompletionSource.SetException(ex);
+				}
+			});
+
+			return await taskCompletionSource.Task;
+		}
 	}
 }

Xamarin.Forms.Platform.UAP/WindowsTicker.cs

@@ -1,10 +1,15 @@
-using Windows.UI.Xaml.Media;
+using Windows.ApplicationModel.Core;
+using System;
+using Windows.UI.Xaml.Media;
 using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms.Platform.UWP
 {
 	internal class WindowsTicker : Ticker
 	{
+		[ThreadStatic]
+		static Ticker s_ticker;
+
 		protected override void DisableTimer()
 		{
 			CompositionTarget.Rendering -= RenderingFrameEventHandler;
@@ -19,5 +24,22 @@ namespace Xamarin.Forms.Platform.UWP
 		{
 			SendSignals();
 		}
+
+		protected override Ticker GetTickerInstance()
+		{
+			if (CoreApplication.Views.Count > 1)
+			{
+				// We've got multiple windows open, we'll need to use the local ThreadStatic Ticker instead of the 
+				// singleton in the base class 
+				if (s_ticker == null)
+				{
+					s_ticker = new WindowsTicker();
+				}
+
+				return s_ticker;
+			}
+
+			return base.GetTickerInstance();
+		}
 	}
 }