feat: fix memory leakage.

demo/Ursa.Demo/Pages/DialogDemo.axaml

@@ -17,6 +17,10 @@
                 <Run Text="Result: "></Run>
                 <Run Text="{Binding Result}"></Run>
             </TextBlock>
+            <TextBlock>
+                <Run Text="Date: "></Run>
+                <Run Text="{Binding DialogViewModel.Date}"></Run>
+            </TextBlock>
             <Button Command="{Binding ShowGlobalDialogCommand}">Show Dialog</Button>
             <Button Command="{Binding ShowLocalOverlayDialogCommand}">Show Local Overlay Dialog</Button>
             <Button Command="{Binding ShowGlobalOverlayDialogCommand}"> Show Global Overlay Dialog </Button>

demo/Ursa.Demo/ViewModels/DialogDemoViewModel.cs

@@ -23,6 +23,16 @@ public class DialogDemoViewModel: ObservableObject
         set => SetProperty(ref _result, value);
     }
 
+    private DateTime _date;
+
+    public DateTime Date
+    {
+        get => _date;
+        set => SetProperty(ref _date, value);
+    }
+
+    public DialogWithActionViewModel DialogViewModel { get; set; } = new DialogWithActionViewModel();
+
     public DialogDemoViewModel()
     {
         ShowLocalOverlayDialogCommand = new AsyncRelayCommand(ShowLocalOverlayDialog);
@@ -43,8 +53,10 @@ public class DialogDemoViewModel: ObservableObject
 
     private async Task ShowLocalOverlayDialog()
     {
+        var vm = new DialogWithActionViewModel();
         var result = await DialogBox.ShowOverlayAsync<DialogWithAction, DialogWithActionViewModel, bool>(
-            new DialogWithActionViewModel(), "LocalHost");
+            DialogViewModel, "LocalHost");
+        Date = vm.Date;
         Result = result;
     }
 }

src/Ursa.Themes.Semi/Controls/Dialog.axaml

@@ -20,10 +20,6 @@
                             Grid.Row="0"
                             Grid.RowSpan="2"
                             Content="{TemplateBinding Content}" />
-                        <StackPanel Grid.Row="2">
-                            <Button>OK</Button>
-                            <Button>Cancel</Button>
-                        </StackPanel>
                     </Grid>
                 </Border>
             </ControlTemplate>

src/Ursa/Controls/Dialog/DialogControl.cs

@@ -10,8 +10,6 @@ public class DialogControl: ContentControl
 {
     public const string PART_CloseButton = "PART_CloseButton";
     
-    
-    
     private Button? _closeButton;
     public event EventHandler<object?> OnClose;
 
@@ -38,17 +36,22 @@ public class DialogControl: ContentControl
     public Task<T> ShowAsync<T>()
     {
         var tcs = new TaskCompletionSource<T>();
-        this.OnClose+= (sender, args) =>
+
+        void OnCloseHandler(object sender, object? args)
         {
             if (args is T result)
             {
                 tcs.SetResult(result);
+                OnClose-= OnCloseHandler;
             }
             else
             {
-                tcs.SetResult(default);
+                tcs.SetResult(default(T));
+                OnClose-= OnCloseHandler;
             }
-        };
+        }
+
+        this.OnClose += OnCloseHandler;
         return tcs.Task;
     }