feat: add TryGetXXManager to WindowXXManager.

demo/Ursa.Demo/Dialogs/CustomDemoDialog.axaml.cs

@@ -1,8 +1,11 @@
+using System;
 using Avalonia;
 using Avalonia.Controls;
+using Avalonia.Controls.Notifications;
 using Avalonia.Controls.Primitives;
 using Avalonia.VisualTree;
 using Ursa.Controls;
+using WindowNotificationManager = Ursa.Controls.WindowNotificationManager;
 
 namespace Ursa.Demo.Dialogs;
 
@@ -25,6 +28,13 @@ public partial class CustomDemoDialog : UserControl
             _viewModel.NotificationManager = new WindowNotificationManager(visualLayerManager) { MaxItems = 3 };
             _viewModel.ToastManager = new WindowToastManager(visualLayerManager) { MaxItems = 3 };
         }
+
+        WindowNotificationManager.TryGetNotificationManager(visualLayerManager, out var manager);
+        if (manager is not null && _viewModel is not null)
+        {
+            Console.WriteLine(ReferenceEquals(_viewModel.NotificationManager, manager));
+            manager.Position = NotificationPosition.TopCenter;
+        }
     }
 
     protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)

demo/Ursa.Demo/Pages/NotificationDemo.axaml.cs

@@ -1,6 +1,5 @@
 using Avalonia;
 using Avalonia.Controls;
-using Avalonia.LogicalTree;
 using Ursa.Controls;
 using Ursa.Demo.ViewModels;
 
@@ -21,12 +20,11 @@ public partial class NotificationDemo : UserControl
     {
         base.OnAttachedToVisualTree(e);
         var topLevel = TopLevel.GetTopLevel(this);
-        _viewModel.NotificationManager = new WindowNotificationManager(topLevel) { MaxItems = 3 };
-    }
 
-    protected override void OnDetachedFromLogicalTree(LogicalTreeAttachmentEventArgs e)
-    {
-        base.OnDetachedFromLogicalTree(e);
-        _viewModel.NotificationManager?.Uninstall();
+        WindowNotificationManager.TryGetNotificationManager(topLevel, out var manager);
+        if (manager is not null)
+        {
+            _viewModel.NotificationManager = manager;
+        }
     }
 }

demo/Ursa.Demo/ViewModels/MainViewViewModel.cs

@@ -1,16 +1,19 @@
 using System;
 using System.Collections.ObjectModel;
 using Avalonia;
+using Avalonia.Controls.Notifications;
 using Avalonia.Styling;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Messaging;
-using Ursa.Controls;
 using Ursa.Themes.Semi;
+using Notification = Ursa.Controls.Notification;
+using WindowNotificationManager = Ursa.Controls.WindowNotificationManager;
 
 namespace Ursa.Demo.ViewModels;
 
 public partial class MainViewViewModel : ViewModelBase
 {
+    public WindowNotificationManager? NotificationManager { get; set; }
     public MenuViewModel Menus { get; set; } = new MenuViewModel();
 
     private object? _content;
@@ -107,6 +110,10 @@ public partial class MainViewViewModel : ViewModelBase
         if (app is not null)
         {
             app.RequestedThemeVariant = newValue.Theme;
+            NotificationManager?.Show(
+                new Notification("Theme changed", $"Theme changed to {newValue.Name}"),
+                type: NotificationType.Success,
+                classes: ["Light"]);
         }
     }
 

demo/Ursa.Demo/Views/MainView.axaml.cs

@@ -1,11 +1,28 @@
+using Avalonia;
 using Avalonia.Controls;
+using Ursa.Controls;
+using Ursa.Demo.ViewModels;
 
 namespace Ursa.Demo.Views;
 
 public partial class MainView : UserControl
 {
+    private MainViewViewModel? _viewModel;
+
     public MainView()
     {
         InitializeComponent();
     }
+
+    protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToVisualTree(e);
+        _viewModel = DataContext as MainViewViewModel;
+        var topLevel = TopLevel.GetTopLevel(this);
+        WindowNotificationManager.TryGetNotificationManager(topLevel, out var manager);
+        if (manager is not null && _viewModel is not null)
+        {
+            _viewModel.NotificationManager = manager;
+        }
+    }
 }

demo/Ursa.Demo/Views/MainWindow.axaml.cs

@@ -5,9 +5,12 @@ namespace Ursa.Demo.Views;
 
 public partial class MainWindow : UrsaWindow
 {
+    public WindowNotificationManager? NotificationManager { get; set; }
+
     public MainWindow()
     {
         InitializeComponent();
+        NotificationManager = new WindowNotificationManager(this) { MaxItems = 3 };
     }
 
     protected override async Task<bool> CanClose()