fix: Hide open flyouts when MessageDialog is shown

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

@@ -55,7 +55,8 @@ static Application()
 			ApiInformation.RegisterAssembly(typeof(Application).Assembly);
 			ApiInformation.RegisterAssembly(typeof(Windows.Storage.ApplicationData).Assembly);
 
-			Uno.DispatcherTimerHelper.SetDispatcherTimerGetter(() => new DispatcherTimer());
+			Uno.Helpers.DispatcherTimerProxy.SetDispatcherTimerGetter(() => new DispatcherTimer());
+			Uno.Helpers.VisualTreeHelperProxy.SetCloseAllPopupsAction(() => Media.VisualTreeHelper.CloseAllPopups());
 
 			InitializePartialStatic();
 		}

src/Uno.UWP/Uno/DispatcherTimerHelper.cs → src/Uno.UWP/Helpers/DispatcherTimerProxy.cs

@@ -1,12 +1,10 @@
 #nullable enable
 
 using System;
-using System.Collections.Generic;
-using System.Text;
 
-namespace Uno
+namespace Uno.Helpers
 {
-	internal static class DispatcherTimerHelper
+	internal static class DispatcherTimerProxy
 	{
 		private static Func<IDispatcherTimer>? _getter;
 

src/Uno.UWP/Helpers/VisualTreeHelperProxy.cs

@@ -0,0 +1,15 @@
+#nullable enable
+
+using System;
+
+namespace Uno.Helpers
+{
+	internal static class VisualTreeHelperProxy
+	{
+		private static Action? _closeAllPopups;
+
+		public static void CloseAllPopups() => _closeAllPopups?.Invoke();
+
+		public static void SetCloseAllPopupsAction(Action closeAllPopups) => _closeAllPopups = closeAllPopups;
+	}
+}

src/Uno.UWP/UI/Popups/MessageDialog.cs

@@ -5,6 +5,7 @@
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using Uno.Helpers;
 using Windows.Foundation;
 using Windows.UI.Core;
 
@@ -52,6 +53,8 @@ public MessageDialog(string content, string title)
 
 		public IAsyncOperation<IUICommand> ShowAsync()
 		{
+			VisualTreeHelperProxy.CloseAllPopups();
+
 			var invokedCommand = new TaskCompletionSource<IUICommand>();
 
 			return AsyncOperation.FromTask<IUICommand>(async ct =>