fix(DialogHost): Improve reliability of visual state monitoring

src/MaterialDesignThemes.Wpf/DialogHost.cs

@@ -667,14 +667,9 @@ public override void OnApplyTemplate()
 
         VisualStateManager.GoToState(this, GetStateName(), false);
 
-        if (GetTemplateChild(RootContentPartName) is FrameworkElement root &&
-            VisualStateManager.GetVisualStateGroups(root) is [VisualStateGroup stateGroup, ..])
+        if (GetTemplateChild(RootContentPartName) is FrameworkElement root)
         {
-            var stateNames = stateGroup.States.OfType<VisualState>().Select(x => x.Name).ToList();
-            if (stateNames.Contains(OpenStateName) && stateNames.Contains(ClosedStateName))
-            {
-                _visualStateMonitor = new(stateGroup);
-            }
+            _visualStateMonitor = new(root);
         }
         base.OnApplyTemplate();
     }

src/MaterialDesignThemes.Wpf/Internal/VisualStateMonitor.cs

@@ -1,41 +1,73 @@
-using System.Threading;
+using System.Threading;
 
 namespace MaterialDesignThemes.Wpf.Internal;
 
-internal sealed class VisualStateMonitor(VisualStateGroup visualStateGroup)
+public sealed class VisualStateMonitor
 {
-    private readonly VisualStateGroup _visualStateGroup = visualStateGroup ??
-            throw new ArgumentNullException(nameof(visualStateGroup));
+    public static VisualStateMonitor? GetMonitor(DependencyObject obj)
+        => (VisualStateMonitor?)obj.GetValue(MonitorProperty);
+
+    public static void SetMonitor(DependencyObject obj, VisualStateMonitor? value)
+        => obj.SetValue(MonitorProperty, value);
+
+    public static readonly DependencyProperty MonitorProperty =
+        DependencyProperty.RegisterAttached("Monitor", typeof(VisualStateMonitor), typeof(VisualStateMonitor), new PropertyMetadata(null));
+
+    public static string? GetCurrentState(DependencyObject obj)
+        => (string?)obj.GetValue(CurrentStateProperty);
+
+    public static void SetCurrentState(DependencyObject obj, string? value)
+        => obj.SetValue(CurrentStateProperty, value);
+
+    public static readonly DependencyProperty CurrentStateProperty =
+        DependencyProperty.RegisterAttached("CurrentState", typeof(string), typeof(VisualStateMonitor), new PropertyMetadata("", OnCurrentStateChanged));
+
+    private static void OnCurrentStateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+    {
+        if (GetMonitor(d) is { } monitor)
+        {
+            monitor.StateChanged((string)e.NewValue);
+        }
+    }
+
+    private string _currentState = "";
+    private event EventHandler<string>? CurrentStateChanged;
+
+    public VisualStateMonitor(DependencyObject source) => SetMonitor(source, this);
+
+    public void StateChanged(string state)
+    {
+        _currentState = state;
+        CurrentStateChanged?.Invoke(this, state);
+    }
 
     public Task WaitForState(string state, CancellationToken cancellationToken)
     {
-        string currentState = _visualStateGroup.CurrentState.Name;
-        if (currentState == state) return Task.CompletedTask;
+        if (_currentState == state) return Task.CompletedTask;
 
         TaskCompletionSource<string> tcs = new();
 
-        EventHandler<VisualStateChangedEventArgs> stateChanged = null!;
+        EventHandler<string> stateChanged = null!;
         stateChanged = (sender, e) =>
         {
-            if (e.NewState.Name == state)
+            if (e == state)
             {
-                _visualStateGroup.CurrentStateChanged -= stateChanged;
+                CurrentStateChanged -= stateChanged;
                 tcs.TrySetResult(state);
             }
         };
 
         cancellationToken.Register(() =>
         {
-            _visualStateGroup.CurrentStateChanged -= stateChanged;
+            CurrentStateChanged -= stateChanged;
             tcs.TrySetCanceled(cancellationToken);
         });
 
-        _visualStateGroup.CurrentStateChanged += stateChanged;
+        CurrentStateChanged += stateChanged;
 
-        currentState = _visualStateGroup.CurrentState.Name;
-        if (currentState == state)
+        if (_currentState == state)
         {
-            _visualStateGroup.CurrentStateChanged -= stateChanged;
+            CurrentStateChanged -= stateChanged;
 
             return Task.CompletedTask;
         }

src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.DialogHost.xaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf"
+                    xmlns:internal="clr-namespace:MaterialDesignThemes.Wpf.Internal"
                     xmlns:converters="clr-namespace:MaterialDesignThemes.Wpf.Converters"
                     xmlns:convertersInternal="clr-namespace:MaterialDesignThemes.Wpf.Converters.Internal">
   <ResourceDictionary.MergedDictionaries>
@@ -66,6 +67,10 @@
                           </EasingDoubleKeyFrame.EasingFunction>
                         </EasingDoubleKeyFrame>
                       </DoubleAnimationUsingKeyFrames>
+                      <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_DialogHostRoot"
+                                                     Storyboard.TargetProperty="(internal:VisualStateMonitor.CurrentState)">
+                        <DiscreteObjectKeyFrame KeyTime="0:0:0.3" Value="{x:Static wpf:DialogHost.OpenStateName}" />
+                      </ObjectAnimationUsingKeyFrames>
                     </Storyboard>
                   </VisualTransition>
                   <VisualTransition From="{x:Static wpf:DialogHost.OpenStateName}" To="{x:Static wpf:DialogHost.ClosedStateName}">
@@ -108,6 +113,10 @@
                           </EasingDoubleKeyFrame.EasingFunction>
                         </EasingDoubleKeyFrame>
                       </DoubleAnimationUsingKeyFrames>
+                      <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_DialogHostRoot"
+                                                     Storyboard.TargetProperty="(internal:VisualStateMonitor.CurrentState)">
+                        <DiscreteObjectKeyFrame KeyTime="0:0:0.3" Value="{x:Static wpf:DialogHost.ClosedStateName}" />
+                      </ObjectAnimationUsingKeyFrames>
                     </Storyboard>
                   </VisualTransition>
                 </VisualStateGroup.Transitions>
@@ -134,6 +143,10 @@
                                      Storyboard.TargetProperty="ScaleY"
                                      To="1"
                                      Duration="0" />
+                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_DialogHostRoot"
+                                                    Storyboard.TargetProperty="(internal:VisualStateMonitor.CurrentState)">
+                      <DiscreteObjectKeyFrame KeyTime="0" Value="{x:Static wpf:DialogHost.OpenStateName}" />
+                    </ObjectAnimationUsingKeyFrames>
                   </Storyboard>
                 </VisualState>
                 <VisualState Name="{x:Static wpf:DialogHost.ClosedStateName}">
@@ -145,6 +158,10 @@
                                      Storyboard.TargetProperty="Opacity"
                                      To="0"
                                      Duration="0" />
+                    <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PART_DialogHostRoot"
+                                                     Storyboard.TargetProperty="(internal:VisualStateMonitor.CurrentState)">
+                      <DiscreteObjectKeyFrame KeyTime="0" Value="{x:Static wpf:DialogHost.ClosedStateName}" />
+                    </ObjectAnimationUsingKeyFrames>
                   </Storyboard>
                 </VisualState>
               </VisualStateGroup>