removed the thing I thought was smart but turned out to be stupid

Removed coerce value and PropertyChanged delegate on Color and Opacity properties.
Initially just the Color property was taken into account in the renderers, it was built up from Opacity property changed.
That was a mistake since it can sometimes breaks the notify property changed mechanism (for example if you set opacity to 1).

Author: roubachof

Sample/ShadowsSample/Views/DynamicShadows.xaml.cs

@@ -100,7 +100,7 @@ private void AddShade(object sender, EventArgs e)
             }
 
             ((ObservableCollection<Shade>)CatShadows.Shades).Add(
-                new Shade { Offset = new Point(xOffset, yOffset), Color = color, BlurRadius = blur });
+                new Shade { Offset = new Point(xOffset, yOffset), Color = color, Opacity = opacity, BlurRadius = blur });
 
             ShadeInfos.Add(new ShadeInfo($"{xOffset},{yOffset}", color, blur.ToString()));
         }

Shadows/Shadows.Droid/ShadowView.PropertyChanged.cs

@@ -130,6 +130,11 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
                 return;
             }
 
+            if (!Shade.IsShadeProperty(e.PropertyName))
+            {
+                return;
+            }
+
             var shade = (Shade)sender;
             var index = _shadesSource.IndexOf(shade);
             if (index < 0)
@@ -144,6 +149,7 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
             {
                 case nameof(Shade.BlurRadius):
                 case nameof(Shade.Color):
+                case nameof(Shade.Opacity):
                     DrawBitmap(index, shade);
                     Invalidate();
                     break;

Shadows/Shadows.Droid/ShadowView.cs

@@ -325,7 +325,7 @@ public static ShadeInfo FromShade(Context context, Shade shade)
                 // float blurCoeff = 1f + (float)shade.BlurRadius / 20f;
 
                 return new ShadeInfo(
-                    shade.Color.ToAndroid(),
+                    shade.Color.MultiplyAlpha(shade.Opacity).ToAndroid(),
                     context.ToPixels(shade.BlurRadius) * 2,
                     context.ToPixels(shade.Offset.X),
                     context.ToPixels(shade.Offset.Y));

Shadows/Shadows.Tizen/TizenShadowsRenderer.cs

@@ -122,7 +122,11 @@ void UpdateGeometry()
                 if (bottom < sb) bottom = sb;
             }
 
-            var canvasGeometry = new Rect(geometry.X + (int)left, geometry.Y + (int)top, geometry.Width + (int)right - (int)left, geometry.Height + (int)bottom - (int)top);
+            var canvasGeometry = new Rect(
+                geometry.X + (int)left,
+                geometry.Y + (int)top,
+                geometry.Width + (int)right - (int)left,
+                geometry.Height + (int)bottom - (int)top);
             if (_canvasView != null)
             {
                 _canvasView.Geometry = canvasGeometry;
@@ -163,7 +167,13 @@ void OnPaintSurface(object sender, SKPaintSurfaceEventArgs e)
 
                     canvas.Save();
                     canvas.ClipPath(path, SKClipOperation.Difference, true);
-                    paint.ImageFilter = SKImageFilter.CreateDropShadow(scaledOffsetX, scaledOffsetY, scaledBlurRadius, scaledBlurRadius, shade.Color.ToSK(), SKDropShadowImageFilterShadowMode.DrawShadowOnly);
+                    paint.ImageFilter = SKImageFilter.CreateDropShadow(
+                        scaledOffsetX,
+                        scaledOffsetY,
+                        scaledBlurRadius,
+                        scaledBlurRadius,
+                        shade.Color.MultiplyAlpha(shade.Opacity).ToSK(),
+                        SKDropShadowImageFilterShadowMode.DrawShadowOnly);
                     canvas.DrawPath(path, paint);
                     canvas.Restore();
 
@@ -204,6 +214,11 @@ void UpdateCornerRadius(bool initialize)
 
         void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
         {
+            if (!Shade.IsShadeProperty(e.PropertyName))
+            {
+                return;
+            }
+
             var shade = (Shade)sender;
             var index = _shadesSource.IndexOf(shade);
             if (index < 0)
@@ -217,6 +232,7 @@ void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
             {
                 case nameof(Shade.BlurRadius):
                 case nameof(Shade.Color):
+                case nameof(Shade.Opacity):
                 case nameof(Shade.Offset):
                     UpdateGeometry();
                     break;

Shadows/Shadows.UWP/UWPShadowsController.PropertyChanged.cs

@@ -127,6 +127,11 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
                 return;
             }
 
+            if (!Shade.IsShadeProperty(e.PropertyName))
+            {
+                return;
+            }
+
             var shade = (Shade)sender;
             var index = _shadesSource.IndexOf(shade);
             if (index < 0)
@@ -140,6 +145,7 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
             {
                 case nameof(Shade.BlurRadius):
                 case nameof(Shade.Color):
+                case nameof(Shade.Opacity):
                 case nameof(Shade.Offset):
                     UpdateShadeVisual(index, shade);
                     break;

Shadows/Shadows.UWP/UWPShadowsController.cs

@@ -95,8 +95,6 @@ private void DestroyShadows()
             }
         }
 
-       
-
         private void InsertShade(int insertIndex, Shade shade)
         {
             shade.PropertyChanged -= ShadePropertyChanged;
@@ -132,7 +130,7 @@ private void InsertShade(int insertIndex, Shade shade)
 
             var dropShadow = _compositor.CreateDropShadow();
             dropShadow.BlurRadius = (float)shade.BlurRadius * 2;
-            dropShadow.Opacity = 1;
+            dropShadow.Opacity = (float)shade.Opacity;
             dropShadow.Color = shade.Color.ToWindowsColor();
             dropShadow.Offset = new Vector3((float)shade.Offset.X - SafeMargin, (float)shade.Offset.Y - SafeMargin, 0);
             dropShadow.Mask = shadowHost.GetAlphaMask();
@@ -188,7 +186,7 @@ private void UpdateShadeVisual(int index, Shade shade)
         {
             var dropShadow = (DropShadow)_shadowVisuals[index].Shadow;
             dropShadow.BlurRadius = (float)shade.BlurRadius;
-            dropShadow.Opacity = 1;
+            dropShadow.Opacity = (float)shade.Opacity;
             dropShadow.Color = shade.Color.ToWindowsColor();
             dropShadow.Offset = new Vector3((float)shade.Offset.X, (float)shade.Offset.Y, 0);
         }

Shadows/Shadows.iOS/ShadeExtensions.cs

@@ -19,7 +19,7 @@ public static CALayer ToCALayer(this Shade shade)
                     ShadowColor = shade.Color.ToCGColor(),
                     ShadowRadius = (nfloat)shade.BlurRadius / UIScreen.MainScreen.Scale,
                     ShadowOffset = new CGSize(shade.Offset.X, shade.Offset.Y),
-                    ShadowOpacity = 1,
+                    ShadowOpacity = (float)shade.Opacity,
                     MasksToBounds = false,
                     RasterizationScale = UIScreen.MainScreen.Scale,
                     ShouldRasterize = true,

Shadows/Shadows.iOS/iOSShadowsController.PropertyChanged.cs

@@ -132,6 +132,11 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
                 return;
             }
 
+            if (!Shade.IsShadeProperty(e.PropertyName))
+            {
+                return;
+            }
+
             var shade = (Shade)sender;
             var index = _shadesSource.IndexOf(shade);
             if (index < 0)
@@ -145,6 +150,7 @@ private void ShadePropertyChanged(object sender, PropertyChangedEventArgs e)
             {
                 case nameof(Shade.BlurRadius):
                 case nameof(Shade.Color):
+                case nameof(Shade.Opacity):
                 case nameof(Shade.Offset):
                     UpdateShadeLayer(index, shade);
                     break;

Shadows/Shadows/AssemblyInfo.cs

@@ -1,10 +1,10 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
-//     Ce code a été généré par un outil.
-//     Version du runtime :4.0.30319.42000
+//     This code was generated by a tool.
+//     Runtime Version:4.0.30319.42000
 //
-//     Les modifications apportées à ce fichier peuvent provoquer un comportement incorrect et seront perdues si
-//     le code est régénéré.
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
 // </auto-generated>
 //------------------------------------------------------------------------------
 

Shadows/Shadows/Shade.cs

@@ -15,42 +15,13 @@ public class Shade : Element
             nameof(Color),
             typeof(Color),
             typeof(Shade),
-            defaultValueCreator: _ => DefaultColor,
-            coerceValue: (bo, v) =>
-                {
-                    var shade = (Shade)bo;
-                    var color = (Color)v;
-                    if (shade.Opacity < 1 && color.A == 1f)
-                    {
-                        // Color is plain and a Opacity is set, add Alpha
-                        return color.MultiplyAlpha(shade.Opacity);
-                    }
-
-                    return color;
-                },
-            propertyChanged: (bo, oldValue, newValue) =>
-                {
-                    var shade = (Shade)bo;
-                    var color = (Color)newValue;
-                    if (color.A < 1 && shade.Opacity == 1f)
-                    {
-                        // Color has alpha and a Opacity is not set, update Opacity
-                        shade.Opacity = color.A;
-                    }
-                });
+            defaultValueCreator: _ => DefaultColor);
 
         public static readonly BindableProperty OpacityProperty = BindableProperty.Create(
             nameof(Opacity),
             typeof(double),
             typeof(Shade),
-            defaultValue: DefaultOpacity,
-            propertyChanged: (bo, oldValue, newValue) =>
-                {
-                    var shade = (Shade)bo;
-                    var previousColor = shade.Color;
-                    var newOpacity = (double)newValue;
-                    shade.Color = new Color(previousColor.R, previousColor.G, previousColor.B, newOpacity);
-                });
+            defaultValue: DefaultOpacity);
 
         public static readonly BindableProperty BlurRadiusProperty = BindableProperty.Create(
             nameof(BlurRadius),
@@ -90,6 +61,14 @@ public double BlurRadius
             set => SetValue(BlurRadiusProperty, value);
         }
 
+        public static bool IsShadeProperty(string propertyName)
+        {
+            return propertyName == nameof(Offset)
+                   || propertyName == nameof(Color)
+                   || propertyName == nameof(Opacity)
+                   || propertyName == nameof(BlurRadius);
+        }
+
         public override string ToString()
         {
             var builder = new StringBuilder();