Add Support for C# Hot Reload (#232)

* Add CommunityToolkitMetadataUpdateHandler

* Include `Type[]` in `ReloadApplication` event

* Add `HotReloadHandler`

* `dotnet format`

* Change `Type[]` -> `IReadOnlyList<Type>`

* Update HotReloadHandler.cs

* Update HotReloadHandler.cs

* Update CommunityToolkit.Maui.Markup.csproj

* Update CommunityToolkitMetadataUpdateHandler.cs

* Update samples/CommunityToolkit.Maui.Markup.Sample/HotReloadHandler.cs

Co-authored-by: Vladislav Antonyuk <[email protected]>

* Add `ICommunityToolkitHotReloadHandler.cs`

* Add `Window` support

* Replace `#if DEBUG` with `[Conditional("DEBUG")]`

* Reference `IServiceProvider` via `Application.Current?.Handler.MauiContext`

* Goto  correct shell route

* Leverage overloaded method

* Change `Debug.WriteLine` -> `Trace.WriteLine`

* Add Null Coalescing Operator to `Handler`

---------

Co-authored-by: Vladislav Antonyuk <[email protected]>

samples/CommunityToolkit.Maui.Markup.Sample/AppShell.cs

@@ -17,9 +17,14 @@ public AppShell(NewsPage newsPage)
 	public static string GetRoute<TPage, TViewModel>() where TPage : BaseContentPage<TViewModel>
 														where TViewModel : BaseViewModel
 	{
-		if (!pageRouteMappingDictionary.TryGetValue(typeof(TPage), out var route))
+		return GetRoute(typeof(TPage));
+	}
+
+	public static string GetRoute(Type type)
+	{
+		if (!pageRouteMappingDictionary.TryGetValue(type, out var route))
 		{
-			throw new KeyNotFoundException($"No map for ${typeof(TPage)} was found on navigation mappings. Please register your ViewModel in {nameof(AppShell)}.{nameof(pageRouteMappingDictionary)}");
+			throw new KeyNotFoundException($"No map for ${type} was found on navigation mappings. Please register your ViewModel in {nameof(AppShell)}.{nameof(pageRouteMappingDictionary)}");
 		}
 
 		return route;

samples/CommunityToolkit.Maui.Markup.Sample/HotReloadHandler.cs

@@ -0,0 +1,75 @@
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+
+namespace CommunityToolkit.Maui.Markup.Sample;
+
+class HotReloadHandler : ICommunityToolkitHotReloadHandler
+{
+	public async void OnHotReload(IReadOnlyList<Type> types)
+	{
+		if (Application.Current?.Windows is null)
+		{
+			Trace.WriteLine($"{nameof(HotReloadHandler)} Failed: {nameof(Application)}.{nameof(Application.Current)}.{nameof(Application.Current.Windows)} is null");
+			return;
+		}
+
+		foreach (var window in Application.Current.Windows)
+		{
+			if (window.Page is not Page currentPage)
+			{
+				return;
+			}
+
+			foreach (var type in types)
+			{
+				if (type.IsSubclassOf(typeof(Page)))
+				{
+					if (window.Page is AppShell shell)
+					{
+						if (shell.CurrentPage is Page visiblePage
+							&& visiblePage.GetType() == type)
+						{
+							var currentPageShellRoute = AppShell.GetRoute(type);
+
+							await currentPage.Dispatcher.DispatchAsync(async () =>
+							{
+								await shell.GoToAsync(currentPageShellRoute, false);
+								shell.Navigation.RemovePage(visiblePage);
+							});
+
+							break;
+						}
+					}
+					else
+					{
+						if (TryGetModalStackPage(window, out var modalPage))
+						{
+							await currentPage.Dispatcher.DispatchAsync(async () =>
+							{
+								await currentPage.Navigation.PopModalAsync(false);
+								await currentPage.Navigation.PushModalAsync(modalPage, false);
+							});
+						}
+						else
+						{
+							await currentPage.Dispatcher.DispatchAsync(async () =>
+							{
+								await currentPage.Navigation.PopAsync(false);
+								await currentPage.Navigation.PushAsync(modalPage, false);
+							});
+						}
+
+						break;
+					}
+				}
+			}
+		}
+	}
+
+
+	static bool TryGetModalStackPage(Window window, [NotNullWhen(true)] out Page? page)
+	{
+		page = window.Navigation.ModalStack.LastOrDefault();
+		return page is not null;
+	}
+}

samples/CommunityToolkit.Maui.Markup.Sample/MauiProgram.cs

@@ -33,6 +33,9 @@ public static MauiApp CreateMauiApp()
 		builder.Services.AddTransient<SettingsPage, SettingsViewModel>();
 		builder.Services.AddTransient<NewsDetailPage, NewsDetailViewModel>();
 
+		// C# Hot Reload Handler
+		builder.Services.AddSingleton<ICommunityToolkitHotReloadHandler, HotReloadHandler>();
+
 		return builder.Build();
 
 		static TimeSpan sleepDurationProvider(int attemptNumber) => TimeSpan.FromSeconds(Math.Pow(2, attemptNumber));

src/CommunityToolkit.Maui.Markup/AppBuilderExtensions.cs

@@ -12,6 +12,19 @@ public static class AppBuilderExtensions
 	/// <returns><see cref="MauiAppBuilder"/> initialized for <see cref="CommunityToolkit.Maui.Markup"/></returns>
 	public static MauiAppBuilder UseMauiCommunityToolkitMarkup(this MauiAppBuilder builder)
 	{
+		RegisterReloadApplicationEventHandler();
 		return builder;
 	}
+
+	[System.Diagnostics.Conditional("DEBUG")]
+	static void RegisterReloadApplicationEventHandler()
+	{
+		CommunityToolkitMetadataUpdateHandler.ReloadApplication += ReloadApplication;
+	}
+
+	static void ReloadApplication(object? sender, IReadOnlyList<Type> e)
+	{
+		var hotReloadHandler = Application.Current?.Handler?.MauiContext?.Services.GetService<ICommunityToolkitHotReloadHandler>();
+		hotReloadHandler?.OnHotReload(e);
+	}
 }

src/CommunityToolkit.Maui.Markup/CommunityToolkitMetadataUpdateHandler.cs

@@ -0,0 +1,21 @@
+[assembly: System.Reflection.Metadata.MetadataUpdateHandler(typeof(CommunityToolkit.Maui.Markup.CommunityToolkitMetadataUpdateHandler))]
+namespace CommunityToolkit.Maui.Markup;
+
+static class CommunityToolkitMetadataUpdateHandler
+{
+	static readonly WeakEventManager reloadApplicationEventHandler = new();
+
+	public static event EventHandler<IReadOnlyList<Type>> ReloadApplication
+	{
+		add => reloadApplicationEventHandler.AddEventHandler(value);
+		remove => reloadApplicationEventHandler.RemoveEventHandler(value);
+	}
+
+	[System.Diagnostics.Conditional("DEBUG")]
+	static void UpdateApplication(Type[]? types)
+	{
+#pragma warning disable CS8625 // Cannot convert null literal to non-nullable reference type.
+		reloadApplicationEventHandler.HandleEvent(null, types?.ToList() ?? Enumerable.Empty<Type>(), nameof(ReloadApplication));
+#pragma warning restore CS8625 // Cannot convert null literal to non-nullable reference type.
+	}
+}

src/CommunityToolkit.Maui.Markup/ICommunityToolkitHotReloadHandler.cs

@@ -0,0 +1,13 @@
+namespace CommunityToolkit.Maui.Markup;
+
+/// <summary>
+/// Interface for handling C# Hot Reload requests
+/// </summary>
+public interface ICommunityToolkitHotReloadHandler
+{
+	/// <summary>
+	/// Executes when C# Hot Reload is invoked
+	/// </summary>
+	/// <param name="types">A <see cref="IReadOnlyList{Type}"/> contianing the types that have been changed in code.</param>
+	void OnHotReload(IReadOnlyList<Type> types);
+}