chore: Improve Suspending event deferral support

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

@@ -35,10 +35,8 @@ partial void OnResumingPartial()
 			Resuming?.Invoke(null, null);
 		}
 
-		partial void OnSuspendingPartial()
-		{
-			Suspending?.Invoke(this, new Windows.ApplicationModel.SuspendingEventArgs(new Windows.ApplicationModel.SuspendingOperation(DateTime.Now.AddSeconds(30))));
-		}
+		private SuspendingOperation CreateSuspendingOperation() =>
+			new SuspendingOperation(DateTimeOffset.Now.AddSeconds(30), null);
 
 		public void Exit()
 		{

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

@@ -302,13 +302,29 @@ internal void OnResuming()
 
 		internal void OnSuspending()
 		{
-			var suspendingEventArgs = new SuspendingEventArgs(new SuspendingOperation(DateTime.Now.AddSeconds(30)));
+			var suspendingOperation = CreateSuspendingOperation();
+			var suspendingEventArgs = new SuspendingEventArgs(suspendingOperation);
+
 			CoreApplication.RaiseSuspending(suspendingEventArgs);
+			Suspending?.Invoke(this, suspendingEventArgs);
+
+			var completedSynchronously = suspendingOperation.DeferralManager.EventRaiseCompleted();
 
-			OnSuspendingPartial();
+#if !__IOS__ && !__ANDROID__ && !__MACOS__
+			// Asynchronous suspension is not supported on all targets, warn the user
+			if (!completedSynchronously && this.Log().IsEnabled(LogLevel.Warning))
+			{
+				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.");
+			}
+#endif
 		}
 
-		partial void OnSuspendingPartial();
+#if !__IOS__ && !__ANDROID__ && !__MACOS__
+		private SuspendinOperation CreateSuspendingOperation() =>
+			new SuspendingOperation(DateTimeOffset.Now.AddSeconds(0), null);
+#endif
 
 		protected virtual void OnWindowCreated(global::Windows.UI.Xaml.WindowCreatedEventArgs args)
 		{

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

@@ -129,14 +129,8 @@ public override void PerformActionForShortcutItem(
 			_preventSecondaryActivationHandling = false;
 		}
 
-		partial void OnSuspendingPartial()
-		{
-			var operation = new SuspendingOperation(DateTime.Now.AddSeconds(10));
-
-			Suspending?.Invoke(this, new SuspendingEventArgs(operation));
-
-			_suspended = true;
-		}
+		private SuspendinOperation CreateSuspendingOperation() =>
+			new SuspendingOperation(DateTimeOffset.Now.AddSeconds(10), () => _suspended = true);
 
 		public override void WillEnterForeground(UIApplication application)
 			=> OnResuming();

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

@@ -91,19 +91,13 @@ public override void DidFinishLaunching(NSNotification notification)
 			}
 		}
 
-		partial void OnSuspendingPartial()
-		{
-			var operation = new SuspendingOperation(DateTime.Now.AddSeconds(30), () =>
+		private SuspendinOperation CreateSuspendingOperation() =>
+			new SuspendingOperation(DateTimeOffset.Now.AddSeconds(30), () =>
 			{
 				Suspended = true;
 				NSApplication.SharedApplication.KeyWindow.PerformClose(null);
 			});
 
-			Suspending?.Invoke(this, new SuspendingEventArgs(operation));
-
-			operation.EventRaiseCompleted();
-		}
-
 		/// <summary>
 		/// This method enables UI Tests to get the output path
 		/// of the current application, in the context of the simulator.

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

@@ -141,20 +141,6 @@ internal static void DispatchSuspending()
 			Current?.OnSuspending();
 		}
 
-		partial void OnSuspendingPartial()
-		{
-			var completed = false;
-			var operation = new SuspendingOperation(DateTime.Now.AddSeconds(0), () => completed = true);
-
-			Suspending?.Invoke(this, new SuspendingEventArgs(operation));
-			operation.EventRaiseCompleted();
-
-			if (!completed && this.Log().IsEnabled(LogLevel.Warning))
-			{
-				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()");

src/Uno.UWP/ApplicationModel/SuspendingOperation.cs

@@ -10,7 +10,7 @@ namespace Windows.ApplicationModel;
 /// </summary>
 public sealed partial class SuspendingOperation : ISuspendingOperation
 {
-	internal SuspendingOperation(DateTimeOffset offset, Action? onComplete = null)
+	internal SuspendingOperation(DateTimeOffset offset, Action? onComplete)
 	{
 		Deadline = offset;
 		DeferralManager = new DeferralManager<SuspendingDeferral>(h => new SuspendingDeferral(h));

src/Uno.UWP/Helpers/DeferralManager.cs

@@ -56,17 +56,21 @@ void OnDeferralCompleted()
 	/// In case the operation is not deferred, it will also synchronously raise
 	/// the Completed event.
 	/// </summary>
-	internal void EventRaiseCompleted() => DeferralCompleted();
+	/// <returns>A value indicating whether the deferral completed synchronously.</returns>
+	internal bool EventRaiseCompleted() => DeferralCompleted();
 
 	internal Task WhenAllCompletedAsync() => _allDeferralsCompletedCompletionSource.Task;
 
-	private void DeferralCompleted()
+	private bool DeferralCompleted()
 	{
 		_deferralsCount--;
 		if (_deferralsCount <= 0)
 		{
 			Completed?.Invoke(this, EventArgs.Empty);
 			_allDeferralsCompletedCompletionSource.TrySetResult(null);
+			return true;
 		}
+
+		return false;
 	}
 }