feat: App/Window activation and visibility on WASM

src/Uno.UI/LinkerDefinition.Wasm.xml

@@ -15,7 +15,8 @@
 	</type>
 	<type fullname="Windows.UI.Xaml.Application">
 	  <method name="DispatchSuspending" />
-	  <method name="DispatchSystemThemeChange" />
+      <method name="DispatchSystemThemeChange" />
+      <method name="DispatchVisibilityChange" />
 	</type>
   </assembly>
 

src/Uno.UI/UI/Xaml/Application.wasm.cs

@@ -44,6 +44,8 @@ public Application()
 			Package.SetEntryAssembly(this.GetType().Assembly);
 
 			CoreDispatcher.Main.RunAsync(CoreDispatcherPriority.Normal, Initialize);
+
+			ObserveApplicationVisibility();
 		}
 
 		[Preserve]
@@ -53,6 +55,27 @@ public static int DispatchSystemThemeChange()
 			return 0;
 		}
 
+		[Preserve]
+		public static int DispatchVisibilityChange(bool isVisible)
+		{
+			var application = Windows.UI.Xaml.Application.Current;
+			var window = Windows.UI.Xaml.Window.Current;
+			if (isVisible)
+			{
+				application?.LeavingBackground?.Invoke(application, new LeavingBackgroundEventArgs());
+				window?.OnVisibilityChanged(true);
+				window?.OnActivated(CoreWindowActivationState.CodeActivated);
+			}
+			else
+			{
+				window?.OnActivated(CoreWindowActivationState.Deactivated);
+				window?.OnVisibilityChanged(false);
+				application?.EnteredBackground?.Invoke(application, new EnteredBackgroundEventArgs());
+			}
+
+			return 0;
+		}
+
 		static partial void StartPartial(ApplicationInitializationCallback callback)
 		{
 			_startInvoked = true;
@@ -74,7 +97,6 @@ public static int DispatchSystemThemeChange()
 			WebAssemblyRuntime.InvokeJS("Windows.UI.Xaml.Application.observeSystemTheme()");
 		}
 
-
 		private void Initialize()
 		{
 			using (WritePhaseEventTrace(TraceProvider.LauchedStart, TraceProvider.LauchedStop))
@@ -124,6 +146,11 @@ internal static void DispatchSuspending()
 				this.Log().LogWarning($"This platform does not support asynchronous Suspending deferral. Code executed after the of the method called by Suspending may not get executed.");
 			}
 		}
+
+		private void ObserveApplicationVisibility()
+		{
+			WebAssemblyRuntime.InvokeJS("Windows.UI.Xaml.Application.observeVisibility()");
+		}
 	}
 }
 #endif

src/Uno.UI/WasmScripts/Uno.UI.d.ts

@@ -1116,8 +1116,10 @@ declare namespace Windows.UI.ViewManagement {
 declare namespace Windows.UI.Xaml {
     class Application {
         private static dispatchThemeChange;
+        private static dispatchVisibilityChange;
         static getDefaultSystemTheme(): string;
         static observeSystemTheme(): void;
+        static observeVisibility(): void;
     }
 }
 declare namespace Windows.UI.Xaml {

src/Uno.UI/WasmScripts/Uno.UI.js

@@ -4037,6 +4037,14 @@ var Windows;
                         });
                     }
                 }
+                static observeVisibility() {
+                    if (!this.dispatchVisibilityChange) {
+                        this.dispatchVisibilityChange = Module.mono_bind_static_method("[Uno.UI] Windows.UI.Xaml.Application:DispatchVisibilityChange");
+                    }
+                    document.addEventListener("visibilitychange", () => {
+                        Application.dispatchVisibilityChange(document.visibilityState == "visible");
+                    });
+                }
             }
             Xaml.Application = Application;
         })(Xaml = UI.Xaml || (UI.Xaml = {}));

src/Uno.UI/ts/Windows/UI/Xaml/Application.ts

@@ -2,6 +2,7 @@
 
 	export class Application {
 		private static dispatchThemeChange: () => number;
+		private static dispatchVisibilityChange: (isVisible: boolean) => number;
 
 		public static getDefaultSystemTheme(): string {
 			if (window.matchMedia) {
@@ -13,19 +14,28 @@
 				}
 			}
 			return null;
-        }
+		}
 
 		public static observeSystemTheme() {
 			if (!this.dispatchThemeChange) {
 				this.dispatchThemeChange = (<any>Module).mono_bind_static_method("[Uno.UI] Windows.UI.Xaml.Application:DispatchSystemThemeChange");
 			}
 
-			if (window.matchMedia)
-			{
+			if (window.matchMedia) {
 				window.matchMedia('(prefers-color-scheme: dark)').addEventListener("change", () => {
 					Application.dispatchThemeChange();
 				});
 			}
 		}
-    }
+
+		public static observeVisibility() {
+			if (!this.dispatchVisibilityChange) {
+				this.dispatchVisibilityChange = (<any>Module).mono_bind_static_method("[Uno.UI] Windows.UI.Xaml.Application:DispatchVisibilityChange");
+			}
+
+			document.addEventListener("visibilitychange", () => {
+				Application.dispatchVisibilityChange(document.visibilityState == "visible");
+			});
+		}
+	}
 }

src/Uno.UWP/ApplicationModel/EnteredBackgroundEventArgs.cs

@@ -2,5 +2,8 @@ namespace Windows.ApplicationModel
 {
 	public partial class EnteredBackgroundEventArgs : IEnteredBackgroundEventArgs
 	{
+		internal EnteredBackgroundEventArgs()
+		{
+		}
 	}
 }

src/Uno.UWP/ApplicationModel/LeavingBackgroundEventArgs.cs

@@ -2,5 +2,8 @@ namespace Windows.ApplicationModel
 {
 	public partial class LeavingBackgroundEventArgs : ILeavingBackgroundEventArgs
 	{
+		internal LeavingBackgroundEventArgs()
+		{
+		}
 	}
 }