Reuse observer instance where possible

src/Avalonia.Base/Layout/Layoutable.cs

@@ -470,14 +470,12 @@ namespace Avalonia.Layout
         protected static void AffectsMeasure<T>(params AvaloniaProperty[] properties)
             where T : Layoutable
         {
-            void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => (e.Sender as T)?.InvalidateMeasure());
-                (e.Sender as T)?.InvalidateMeasure();
-            }
 
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(Invalidate);
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
 
@@ -493,14 +491,12 @@ namespace Avalonia.Layout
         protected static void AffectsArrange<T>(params AvaloniaProperty[] properties)
             where T : Layoutable
         {
-            void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            var invalidate = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => (e.Sender as T)?.InvalidateArrange());
-                (e.Sender as T)?.InvalidateArrange();
-            }
 
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(Invalidate);
+                property.Changed.Subscribe(invalidate);
             }
         }
 

src/Avalonia.Base/Media/Brush.cs

@@ -104,14 +104,12 @@ namespace Avalonia.Media
         protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
             where T : Brush
         {
-            static void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => (e.Sender as T)?.RaiseInvalidated(EventArgs.Empty));
-                (e.Sender as T)?.RaiseInvalidated(EventArgs.Empty);
-            }
 
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(e => Invalidate(e));
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
 

src/Avalonia.Base/Media/DashStyle.cs

@@ -52,13 +52,11 @@ namespace Avalonia.Media
 
         static DashStyle()
         {
-            void RaiseInvalidated(AvaloniaPropertyChangedEventArgs e)
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => ((DashStyle)e.Sender).Invalidated?.Invoke(e.Sender, EventArgs.Empty));
-                ((DashStyle)e.Sender).Invalidated?.Invoke(e.Sender, EventArgs.Empty);
-            }
 
-            DashesProperty.Changed.Subscribe(RaiseInvalidated);
+            DashesProperty.Changed.Subscribe(invalidateObserver);
-            OffsetProperty.Changed.Subscribe(RaiseInvalidated);
+            OffsetProperty.Changed.Subscribe(invalidateObserver);
         }
 
         /// <summary>

src/Avalonia.Base/Media/ExperimentalAcrylicMaterial.cs

@@ -275,14 +275,12 @@ namespace Avalonia.Media
         protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
             where T : ExperimentalAcrylicMaterial
         {
-            static void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => (e.Sender as T)?.RaiseInvalidated(EventArgs.Empty));
-                (e.Sender as T)?.RaiseInvalidated(EventArgs.Empty);
-            }
 
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(e => Invalidate(e));
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
 

src/Avalonia.Base/Media/Geometry.cs

@@ -118,9 +118,10 @@ namespace Avalonia.Media
         /// </remarks>
         protected static void AffectsGeometry(params AvaloniaProperty[] properties)
         {
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(AffectsGeometryInvalidate);
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(AffectsGeometryInvalidate);
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
 

src/Avalonia.Base/Media/ScaleTransform.cs

@@ -26,8 +26,6 @@ namespace Avalonia.Media
         /// </summary>
         public ScaleTransform()
         {
-            this.GetObservable(ScaleXProperty).Subscribe(_ => RaiseChanged());
-            this.GetObservable(ScaleYProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>
@@ -64,5 +62,15 @@ namespace Avalonia.Media
         /// Gets the transform's <see cref="Matrix"/>.
         /// </summary>
         public override Matrix Value => Matrix.CreateScale(ScaleX, ScaleY);
+        
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == ScaleXProperty || change.Property == ScaleYProperty)
+            {
+                RaiseChanged();
+            }
+        }
     }
 }

src/Avalonia.Base/Media/SkewTransform.cs

@@ -26,8 +26,6 @@ namespace Avalonia.Media
         /// </summary>
         public SkewTransform()
         {
-            this.GetObservable(AngleXProperty).Subscribe(_ => RaiseChanged());
-            this.GetObservable(AngleYProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>
@@ -63,5 +61,15 @@ namespace Avalonia.Media
         /// Gets the transform's <see cref="Matrix"/>.
         /// </summary>
         public override Matrix Value => Matrix.CreateSkew(Matrix.ToRadians(AngleX), Matrix.ToRadians(AngleY));
+        
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == AngleXProperty || change.Property == AngleYProperty)
+            {
+                RaiseChanged();
+            }
+        }
     }
 }

src/Avalonia.Base/Media/TranslateTransform.cs

@@ -26,8 +26,6 @@ namespace Avalonia.Media
         /// </summary>
         public TranslateTransform()
         {
-            this.GetObservable(XProperty).Subscribe(_ => RaiseChanged());
-            this.GetObservable(YProperty).Subscribe(_ => RaiseChanged());
         }
 
         /// <summary>
@@ -64,5 +62,15 @@ namespace Avalonia.Media
         /// Gets the transform's <see cref="Matrix"/>.
         /// </summary>
         public override Matrix Value => Matrix.CreateTranslation(X, Y);
+        
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == XProperty || change.Property == YProperty)
+            {
+                RaiseChanged();
+            }
+        }
     }
 }

src/Avalonia.Controls/DefinitionBase.cs

@@ -806,14 +806,12 @@ namespace Avalonia.Controls
         /// <param name="properties">The properties.</param>
         protected static void AffectsParentMeasure(params AvaloniaProperty[] properties)
         {
-            void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
-            {
+                static e => (e.Sender as DefinitionBase)?.Parent?.InvalidateMeasure());
-                (e.Sender as DefinitionBase)?.Parent?.InvalidateMeasure();
-            }
 
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(Invalidate);
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
     }

src/Avalonia.Controls/Panel.cs

@@ -87,9 +87,11 @@ namespace Avalonia.Controls
         protected static void AffectsParentArrange<TPanel>(params AvaloniaProperty[] properties)
             where TPanel : Panel
         {
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
+                static e => AffectsParentArrangeInvalidate<TPanel>(e));
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(AffectsParentArrangeInvalidate<TPanel>);
+                property.Changed.Subscribe(invalidateObserver);
             }
         }
 
@@ -100,9 +102,11 @@ namespace Avalonia.Controls
         protected static void AffectsParentMeasure<TPanel>(params AvaloniaProperty[] properties)
             where TPanel : Panel
         {
+            var invalidateObserver = new AnonymousObserver<AvaloniaPropertyChangedEventArgs>(
+                static e => AffectsParentMeasureInvalidate<TPanel>(e));
             foreach (var property in properties)
             {
-                property.Changed.Subscribe(AffectsParentMeasureInvalidate<TPanel>);
+                property.Changed.Subscribe(invalidateObserver);
             }
         }