Simplify the listening of dependency properties.

Author: qian-o

components/LayoutTransformControl/src/LayoutTransformControl.Properties.cs

@@ -127,6 +127,7 @@ private void UnsubscribeFromTransformPropertyChanges(Transform transform)
         foreach (var propertyChangeEventSource in propertyChangeEventSources)
         {
             propertyChangeEventSource.ValueChanged -= OnTransformPropertyChanged;
+            propertyChangeEventSource.Unregister();
         }
 
         _transformPropertyChangeEventSources.Remove(transform);
@@ -153,7 +154,7 @@ private void SubscribeToTransformPropertyChanges(Transform transform)
 
         if (rotateTransform != null)
         {
-            var anglePropertyChangeEventSource = new PropertyChangeEventSource<double>(rotateTransform, "Angle");
+            var anglePropertyChangeEventSource = new PropertyChangeEventSource<double>(rotateTransform, RotateTransform.AngleProperty);
             anglePropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(anglePropertyChangeEventSource);
             return;
@@ -163,11 +164,11 @@ private void SubscribeToTransformPropertyChanges(Transform transform)
 
         if (scaleTransform != null)
         {
-            var scaleXPropertyChangeEventSource =  new PropertyChangeEventSource<double>(scaleTransform, "ScaleX");
+            var scaleXPropertyChangeEventSource = new PropertyChangeEventSource<double>(scaleTransform, ScaleTransform.ScaleXProperty);
             scaleXPropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(scaleXPropertyChangeEventSource);
 
-            var scaleYPropertyChangeEventSource = new PropertyChangeEventSource<double>(scaleTransform, "ScaleY");
+            var scaleYPropertyChangeEventSource = new PropertyChangeEventSource<double>(scaleTransform, ScaleTransform.ScaleYProperty);
             scaleYPropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(scaleYPropertyChangeEventSource);
             return;
@@ -177,11 +178,11 @@ private void SubscribeToTransformPropertyChanges(Transform transform)
 
         if (skewTransform != null)
         {
-            var angleXPropertyChangeEventSource =  new PropertyChangeEventSource<double>(skewTransform, "AngleX");
+            var angleXPropertyChangeEventSource = new PropertyChangeEventSource<double>(skewTransform, SkewTransform.AngleXProperty);
             angleXPropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(angleXPropertyChangeEventSource);
 
-            var angleYPropertyChangeEventSource = new PropertyChangeEventSource<double>(skewTransform, "AngleY");
+            var angleYPropertyChangeEventSource = new PropertyChangeEventSource<double>(skewTransform, SkewTransform.AngleYProperty);
             angleYPropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(angleYPropertyChangeEventSource);
             return;
@@ -194,7 +195,7 @@ private void SubscribeToTransformPropertyChanges(Transform transform)
             var matrixPropertyChangeEventSource =
                 new PropertyChangeEventSource<double>(
                     matrixTransform,
-                    "Matrix");
+                    MatrixTransform.MatrixProperty);
             matrixPropertyChangeEventSource.ValueChanged += OnTransformPropertyChanged;
             propertyChangeEventSources.Add(matrixPropertyChangeEventSource);
         }

components/LayoutTransformControl/src/PropertyChangeEventSource.cs

@@ -8,87 +8,38 @@ namespace CommunityToolkit.WinUI.Controls;
 /// Allows raise an event when the value of a dependency property changes when a view model is otherwise not necessary.
 /// </summary>
 /// <typeparam name="TPropertyType">Type of the DependencyProperty</typeparam>
-internal partial class PropertyChangeEventSource<TPropertyType> : FrameworkElement
+internal partial class PropertyChangeEventSource<TPropertyType>
 {
     private readonly DependencyObject _source;
+    private readonly DependencyProperty _property;
+    private readonly long _token;
 
     /// <summary>
     /// Occurs when the value changes.
     /// </summary>
     public event EventHandler<TPropertyType> ValueChanged;
 
-    /// <summary>
-    /// Value Dependency Property
-    /// </summary>
-    public static readonly DependencyProperty ValueProperty =
-        DependencyProperty.Register(
-            "Value",
-            typeof(TPropertyType),
-            typeof(PropertyChangeEventSource<TPropertyType>),
-            new PropertyMetadata(default(TPropertyType), OnValueChanged));
-
-    /// <summary>
-    /// Gets or sets the Value property. This dependency property
-    /// indicates the value.
-    /// </summary>
-    public TPropertyType Value
-    {
-        get { return (TPropertyType)GetValue(ValueProperty); }
-        set { SetValue(ValueProperty, value); }
-    }
-
-    /// <summary>
-    /// Handles changes to the Value property.
-    /// </summary>
-    /// <param name="d">
-    /// The <see cref="DependencyObject"/> on which the property has changed value.
-    /// </param>
-    /// <param name="e">
-    /// Event data that is issued by any event that
-    /// tracks changes to the effective value of this property.
-    /// </param>
-    private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
-    {
-        var target = (PropertyChangeEventSource<TPropertyType>)d;
-        TPropertyType oldValue = (TPropertyType)e.OldValue;
-        TPropertyType newValue = target.Value;
-        target.OnValueChanged(oldValue, newValue);
-    }
-
-    /// <summary>
-    /// Provides derived classes an opportunity to handle changes to the Value property.
-    /// </summary>
-    /// <param name="oldValue">The old Value value</param>
-    /// <param name="newValue">The new Value value</param>
-    private void OnValueChanged(TPropertyType oldValue, TPropertyType newValue)
-    {
-        ValueChanged?.Invoke(_source, newValue);
-    }
-
     /// <summary>
     /// Initializes a new instance of the <see cref="PropertyChangeEventSource{TPropertyType}"/> class.
     /// </summary>
     /// <param name="source">The source.</param>
-    /// <param name="propertyName">Name of the property.</param>
-    /// <param name="bindingMode">The binding mode.</param>
+    /// <param name="property">Monitor this dependency property for changes.</param>
 #pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
     public PropertyChangeEventSource(
 #pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
         DependencyObject source,
-        string propertyName,
-        BindingMode bindingMode = BindingMode.TwoWay)
+        DependencyProperty property)
     {
         _source = source;
+        _property = property;
+        _token = source.RegisterPropertyChangedCallback(property, (_, _) =>
+        {
+            ValueChanged?.Invoke(this, (TPropertyType)source.GetValue(property));
+        });
+    }
 
-        // Bind to the property to be able to get its changes relayed as events through the ValueChanged event.
-        var binding =
-            new Binding
-            {
-                Source = source,
-                Path = new PropertyPath(propertyName),
-                Mode = bindingMode
-            };
-
-        SetBinding(ValueProperty, binding);
+    public void Unregister()
+    {
+        _source.UnregisterPropertyChangedCallback(_property, _token);
     }
 }