fix(Maui): pop dialog from stack before ShowDialogAsync callback

Remove the dialog from IDialogContainer.DialogStack before invoking the
completion callback so callers can navigate immediately after the dialog
closes (GitHub #3395).

Add DryIoc regression test covering GoBackAsync after ShowDialogAsync.

Author: dansiegel

src/Maui/Prism.Maui/Dialogs/DialogServiceBase.cs

@@ -46,6 +46,11 @@ async Task DialogAware_RequestClose(IDialogResult outResult)
                         return;
                     }
 
+                    // Remove before callbacks so ShowDialogAsync's synchronous TrySetResult cannot resume
+                    // callers that run GoBackAsync while the stack still shows this modal (#3395).
+                    if (dialogModal is not null)
+                        IDialogContainer.DialogStack.Remove(dialogModal);
+
                     await callback.Invoke(result);
                     GC.Collect();
                 }

tests/Maui/Prism.DryIoc.Maui.Tests/Fixtures/Navigation/DialogNavigationRegressionFixture.cs

@@ -0,0 +1,48 @@
+using Prism.Dialogs;
+using Prism.DryIoc.Maui.Tests.Mocks.ViewModels;
+using Prism.DryIoc.Maui.Tests.Mocks.Views;
+using Prism.Ioc;
+using Prism.Navigation.Xaml;
+
+namespace Prism.DryIoc.Maui.Tests.Fixtures.Navigation;
+
+/// <summary>Regression tests for dialog + navigation interactions (GitHub #3395).</summary>
+public class DialogNavigationRegressionFixture : TestBase
+{
+    public DialogNavigationRegressionFixture(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
+    {
+    }
+
+    [Fact]
+    public async Task Issue3395_GoBackAsync_After_ShowDialogAsync_Completes_Pops_Navigation_Page()
+    {
+        var mauiApp = CreateBuilder(prism => prism
+                .RegisterTypes(c =>
+                {
+                    c.RegisterDialog<TestDialogView, TestDialogViewModel>("TestDialog");
+                })
+                .CreateWindow("NavigationPage/MockViewA/MockViewB"))
+            .Build();
+        var window = GetWindow(mauiApp);
+        var navPage = Assert.IsAssignableFrom<Microsoft.Maui.Controls.NavigationPage>(window.Page);
+        Assert.IsType<MockViewB>(navPage.CurrentPage);
+        Assert.Equal(2, navPage.Navigation.NavigationStack.Count);
+
+        var container = navPage.CurrentPage.GetContainerProvider();
+        var dialogService = container.Resolve<IDialogService>();
+        var navigationService = Prism.Navigation.Xaml.Navigation.GetNavigationService(navPage.CurrentPage);
+
+        var dialogResult = await dialogService.ShowDialogAsync("TestDialog");
+        Assert.NotNull(dialogResult);
+        Assert.Null(dialogResult.Exception);
+        Assert.Equal(ButtonResult.OK, dialogResult.Result);
+        Assert.Empty(IDialogContainer.DialogStack);
+
+        var goBackResult = await navigationService.GoBackAsync();
+        Assert.True(goBackResult.Success);
+        Assert.Null(goBackResult.Exception);
+        Assert.IsType<MockViewA>(navPage.CurrentPage);
+        Assert.Single(navPage.Navigation.NavigationStack);
+    }
+}

tests/Maui/Prism.DryIoc.Maui.Tests/Mocks/ViewModels/TestDialogViewModel.cs

@@ -0,0 +1,31 @@
+using Prism.Dialogs;
+using Prism.Mvvm;
+
+namespace Prism.DryIoc.Maui.Tests.Mocks.ViewModels;
+
+/// <summary>Minimal <see cref="IDialogAware"/> for dialog regression tests; view closes itself on <see cref="VisualElement.Loaded"/>.</summary>
+public class TestDialogViewModel : BindableBase, IDialogAware
+{
+    private DialogCloseListener _requestClose;
+
+    public TestDialogViewModel()
+    {
+        _requestClose = new DialogCloseListener();
+    }
+
+    public DialogCloseListener RequestClose
+    {
+        get => _requestClose;
+        set => SetProperty(ref _requestClose, value);
+    }
+
+    public bool CanCloseDialog() => true;
+
+    public void OnDialogClosed()
+    {
+    }
+
+    public void OnDialogOpened(IDialogParameters parameters)
+    {
+    }
+}

tests/Maui/Prism.DryIoc.Maui.Tests/Mocks/Views/TestDialogView.cs

@@ -0,0 +1,20 @@
+using Prism.Dialogs;
+
+namespace Prism.DryIoc.Maui.Tests.Mocks.Views;
+
+/// <summary>Border-based dialog; auto-closes on <see cref="VisualElement.Loaded"/> after <see cref="IDialogContainer.DialogView"/> is wired.</summary>
+public class TestDialogView : Border
+{
+    public TestDialogView()
+    {
+        Content = new Label { Text = "TestDialog" };
+        Loaded += OnLoaded;
+    }
+
+    private void OnLoaded(object? sender, EventArgs e)
+    {
+        Loaded -= OnLoaded;
+        if (BindingContext is IDialogAware aware)
+            aware.RequestClose.Invoke(ButtonResult.OK);
+    }
+}