Iterated a bit on the dialog view model design, it now uses the UI dispatcher to ensure the Close() method is invoked in the UI thread

Source/AutoBinding/ConventionBinder.cs

@@ -62,25 +62,36 @@ namespace Nuclex.Avalonia.AutoBinding {
       if(dialogViewModel != null) {
         Window? viewAsWindow = view as Window;
         if(viewAsWindow != null) {
-          EventHandler<DialogResultEventArgs> handler = (
+          bindViewModelSubmitToDialogClose(viewAsWindow, dialogViewModel);
-            delegate(object sender, DialogResultEventArgs arguments) {
-              viewAsWindow.Close(arguments.Result);
-            }
-          );
-
-          dialogViewModel.Submitted += handler;
-
-          // Does this help anything?
-          // Without it, the view has a reference to the view model (via DataContext),
-          // and the view model references the view (via event subscription), but this
-          // shouldn't bother the .NET garbage collector at all.
-          viewAsWindow.Closed += delegate(object sender, EventArgs arguments) {
-            dialogViewModel.Submitted -= handler;
-          };
         }
       }
     }
 
+    /// <summary>
+    ///   Convention binding for view models with a 'Submit' event,
+    ///   closes the dialog when the view model fires the event
+    /// </summary>
+    /// <param name="dialogWindow">Window the displays the dialog's UI</param>
+    /// <param name="dialogViewModel">View model that has the 'Submit' event</param>
+    private static void bindViewModelSubmitToDialogClose(
+      Window dialogWindow, IDialogViewModel dialogViewModel
+    ) {
+      EventHandler<DialogResultEventArgs> handler = (
+        delegate(object sender, DialogResultEventArgs arguments) {
+          dialogWindow.Close(arguments.Result);
+        }
+      );
+
+      dialogViewModel.Submitted += handler;
+
+      // Does this help anything?
+      // Without it, the view has a reference to the view model (via DataContext),
+      // and the view model references the view (via event subscription), but this
+      // shouldn't bother the .NET garbage collector at all.
+      dialogWindow.Closed += delegate (object sender, EventArgs arguments) {
+        dialogViewModel.Submitted -= handler;
+      };
+    }
   }
 
 } // namespace Nuclex.Avalonia.AutoBinding

Source/ViewModels/DialogResultEventArgs.cs

@@ -26,17 +26,17 @@ namespace Nuclex.Avalonia.ViewModels {
 
     /// <summary>Initializes a new dialog result event argument container</summary>
     /// <param name="result">Result the dialog should exit with</param>
-    public DialogResultEventArgs(object result) {
+    public DialogResultEventArgs(object? result) {
       this.result = result;
     }
 
     /// <summary>Result that should be returned from the dialog</summary>
-    public object Result {
+    public object? Result {
       get { return this.result; }
     }
 
     /// <summary>Result that should be returned from the dialog</summary>
-    private readonly object result;
+    private readonly object? result;
 
   }
 

Source/ViewModels/IDialogViewModel.cs

@@ -18,7 +18,6 @@ limitations under the License.
 #endregion // Apache License 2.0
 
 using System;
-using System.Threading.Tasks;
 
 using Nuclex.Avalonia.ViewModels;
 
@@ -30,11 +29,6 @@ namespace Nuclex.Avalonie.ViewModels {
     /// <summary>Indicates that the view should close</summary>
     event EventHandler<DialogResultEventArgs> Submitted;
 
-    /// <summary>Indicates that the dialog should be closed</summary>
-    /// <param name="dialogResult">Result the dialog should return</param>
-    /// <returns>A task that finishes when the submit notification has been sent</returns>
-    Task SubmitAsync(object? dialogResult = null);
-
   }
 
 } // namespace Nuclex.Avalonie.ViewModels