Make brushes raise a Changed event.

When their visual representation changes.

src/Avalonia.Visuals/Media/Brush.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Media
     /// Describes how an area is painted.
     /// </summary>
     [TypeConverter(typeof(BrushConverter))]
-    public abstract class Brush : AvaloniaObject, IBrush
+    public abstract class Brush : AvaloniaObject, IMutableBrush
     {
         /// <summary>
         /// Defines the <see cref="Opacity"/> property.
@@ -18,6 +18,9 @@ namespace Avalonia.Media
         public static readonly StyledProperty<double> OpacityProperty =
             AvaloniaProperty.Register<Brush, double>(nameof(Opacity), 1.0);
 
+        /// <inheritdoc/>
+        public event EventHandler Changed;
+
         /// <summary>
         /// Gets or sets the opacity of the brush.
         /// </summary>
@@ -50,5 +53,36 @@ namespace Avalonia.Media
 
             throw new FormatException($"Invalid brush string: '{s}'.");
         }
+
+        /// <inheritdoc/>
+        public abstract IBrush ToImmutable();
+
+        /// <summary>
+        /// Marks a property as affecting the brush's visual representation.
+        /// </summary>
+        /// <param name="properties">The properties.</param>
+        /// <remarks>
+        /// After a call to this method in a brush's static constructor, any change to the
+        /// property will cause the <see cref="Changed"/> event to be raised on the brush.
+        /// </remarks>
+        protected static void AffectsRender<T>(params AvaloniaProperty[] properties)
+            where T : Brush
+        {
+            void Invalidate(AvaloniaPropertyChangedEventArgs e)
+            {
+                (e.Sender as T)?.RaiseChanged(EventArgs.Empty);
+            }
+
+            foreach (var property in properties)
+            {
+                property.Changed.Subscribe(Invalidate);
+            }
+        }
+
+        /// <summary>
+        /// Raises the <see cref="Changed"/> event.
+        /// </summary>
+        /// <param name="e">The event args.</param>
+        protected void RaiseChanged(EventArgs e) => Changed?.Invoke(this, e);
     }
 }

src/Avalonia.Visuals/Media/GradientBrush.cs

@@ -1,7 +1,11 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
 using System.Collections.Generic;
+using System.Collections.Specialized;
+using System.ComponentModel;
+using Avalonia.Collections;
 using Avalonia.Metadata;
 
 namespace Avalonia.Media
@@ -20,35 +24,74 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="GradientStops"/> property.
         /// </summary>
-        public static readonly StyledProperty<IList<GradientStop>> GradientStopsProperty =
-            AvaloniaProperty.Register<GradientBrush, IList<GradientStop>>(nameof(GradientStops));
+        public static readonly StyledProperty<GradientStops> GradientStopsProperty =
+            AvaloniaProperty.Register<GradientBrush, GradientStops>(nameof(GradientStops));
+
+        private IDisposable _gradientStopsSubscription;
+
+        static GradientBrush()
+        {
+            GradientStopsProperty.Changed.Subscribe(GradientStopsChanged);
+            AffectsRender<LinearGradientBrush>(SpreadMethodProperty);
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="GradientBrush"/> class.
         /// </summary>
         public GradientBrush()
         {
-            this.GradientStops = new List<GradientStop>();
+            this.GradientStops = new GradientStops();
         }
 
-        /// <summary>
-        /// Gets or sets the brush's spread method that defines how to draw a gradient that
-        /// doesn't fill the bounds of the destination control.
-        /// </summary>
+        /// <inheritdoc/>
         public GradientSpreadMethod SpreadMethod
         {
             get { return GetValue(SpreadMethodProperty); }
             set { SetValue(SpreadMethodProperty, value); }
         }
 
-        /// <summary>
-        /// Gets or sets the brush's gradient stops.
-        /// </summary>
+        /// <inheritdoc/>
         [Content]
-        public IList<GradientStop> GradientStops
+        public GradientStops GradientStops
         {
             get { return GetValue(GradientStopsProperty); }
             set { SetValue(GradientStopsProperty, value); }
         }
+
+        /// <inheritdoc/>
+        IReadOnlyList<IGradientStop> IGradientBrush.GradientStops => GradientStops;
+
+        private static void GradientStopsChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Sender is GradientBrush brush)
+            {
+                var oldValue = (GradientStops)e.OldValue;
+                var newValue = (GradientStops)e.NewValue;
+
+                if (oldValue != null)
+                {
+                    oldValue.CollectionChanged -= brush.GradientStopsChanged;
+                    brush._gradientStopsSubscription.Dispose();
+                }
+
+                if (newValue != null)
+                {
+                    newValue.CollectionChanged += brush.GradientStopsChanged;
+                    brush._gradientStopsSubscription = newValue.TrackItemPropertyChanged(brush.GradientStopChanged);
+                }
+
+                brush.RaiseChanged(EventArgs.Empty);
+            }
+        }
+
+        private void GradientStopsChanged(object sender, NotifyCollectionChangedEventArgs e)
+        {
+            RaiseChanged(EventArgs.Empty);
+        }
+
+        private void GradientStopChanged(Tuple<object, PropertyChangedEventArgs> e)
+        {
+            RaiseChanged(EventArgs.Empty);
+        }
     }
 }

src/Avalonia.Visuals/Media/GradientStop.cs

@@ -4,10 +4,22 @@
 namespace Avalonia.Media
 {
     /// <summary>
-    /// GradientStop
+    /// Describes the location and color of a transition point in a gradient.
     /// </summary>
-    public sealed class GradientStop
+    public sealed class GradientStop : AvaloniaObject, IGradientStop
     {
+        /// <summary>
+        /// Describes the <see cref="Offset"/> property.
+        /// </summary>
+        public static StyledProperty<double> OffsetProperty =
+            AvaloniaProperty.Register<GradientStop, double>(nameof(Offset));
+
+        /// <summary>
+        /// Describes the <see cref="Color"/> property.
+        /// </summary>
+        public static StyledProperty<Color> ColorProperty =
+            AvaloniaProperty.Register<GradientStop, Color>(nameof(Color));
+
         /// <summary>
         /// Initializes a new instance of the <see cref="GradientStop"/> class.
         /// </summary>
@@ -24,16 +36,18 @@ namespace Avalonia.Media
             Offset = offset;
         }
 
-        // TODO: Make these dependency properties.
-
-        /// <summary>
-        /// The offset
-        /// </summary>
-        public double Offset { get; set; }
+        /// <inheritdoc/>
+        public double Offset
+        {
+            get => GetValue(OffsetProperty);
+            set => SetValue(OffsetProperty, value);
+        }
 
-        /// <summary>
-        /// The color
-        /// </summary>
-        public Color Color { get; set; }
+        /// <inheritdoc/>
+        public Color Color
+        {
+            get => GetValue(ColorProperty);
+            set => SetValue(ColorProperty, value);
+        }
     }
-}
+}

src/Avalonia.Visuals/Media/GradientStops.cs

@@ -0,0 +1,23 @@
+using System.Collections.Generic;
+using System.Linq;
+using Avalonia.Collections;
+using Avalonia.Media.Immutable;
+
+namespace Avalonia.Media
+{
+    /// <summary>
+    /// A collection of <see cref="GradientStop"/>s.
+    /// </summary>
+    public class GradientStops : AvaloniaList<GradientStop>
+    {
+        public GradientStops()
+        {
+            ResetBehavior = ResetBehavior.Remove;
+        }
+
+        public IReadOnlyList<ImmutableGradientStop> ToImmutable()
+        {
+            return this.Select(x => new ImmutableGradientStop(x.Offset, x.Color)).ToList();
+        }
+    }
+}

src/Avalonia.Visuals/Media/IGradientBrush.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets the brush's gradient stops.
         /// </summary>
-        IList<GradientStop> GradientStops { get; }
+        IReadOnlyList<IGradientStop> GradientStops { get; }
 
         /// <summary>
         /// Gets the brush's spread method that defines how to draw a gradient that doesn't fill
@@ -18,4 +18,4 @@ namespace Avalonia.Media
         /// </summary>
         GradientSpreadMethod SpreadMethod { get; }
     }
-}
+}

src/Avalonia.Visuals/Media/IGradientStop.cs

@@ -0,0 +1,18 @@
+namespace Avalonia.Media
+{
+    /// <summary>
+    /// Describes the location and color of a transition point in a gradient.
+    /// </summary>
+    public interface IGradientStop
+    {
+        /// <summary>
+        /// Gets the gradient stop color.
+        /// </summary>
+        Color Color { get; }
+
+        /// <summary>
+        /// Gets the gradient stop offset.
+        /// </summary>
+        double Offset { get; }
+    }
+}

src/Avalonia.Visuals/Media/IMutableBrush.cs

@@ -1,10 +1,17 @@
-namespace Avalonia.Media
+using System;
+
+namespace Avalonia.Media
 {
     /// <summary>
     /// Represents a mutable brush which can return an immutable clone of itself.
     /// </summary>
     public interface IMutableBrush : IBrush
     {
+        /// <summary>
+        /// Raised when the brush changes visually.
+        /// </summary>
+        event EventHandler Changed;
+
         /// <summary>
         /// Creates an immutable clone of the brush.
         /// </summary>

src/Avalonia.Visuals/Media/ImageBrush.cs

@@ -2,13 +2,14 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using Avalonia.Media.Imaging;
+using Avalonia.Media.Immutable;
 
 namespace Avalonia.Media
 {
     /// <summary>
     /// Paints an area with an <see cref="IBitmap"/>.
     /// </summary>
-    public class ImageBrush : TileBrush, IImageBrush, IMutableBrush
+    public class ImageBrush : TileBrush, IImageBrush
     {
         /// <summary>
         /// Defines the <see cref="Visual"/> property.
@@ -16,6 +17,11 @@ namespace Avalonia.Media
         public static readonly StyledProperty<IBitmap> SourceProperty =
             AvaloniaProperty.Register<ImageBrush, IBitmap>(nameof(Source));
 
+        static ImageBrush()
+        {
+            AffectsRender<ImageBrush>(SourceProperty);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ImageBrush"/> class.
         /// </summary>
@@ -42,9 +48,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        IBrush IMutableBrush.ToImmutable()
+        public override IBrush ToImmutable()
         {
-            return new Immutable.ImmutableImageBrush(this);
+            return new ImmutableImageBrush(this);
         }
     }
 }

src/Avalonia.Visuals/Media/Immutable/ImmutableGradientBrush.cs

@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-using System.Linq;
 
 namespace Avalonia.Media.Immutable
 {
@@ -15,7 +14,7 @@ namespace Avalonia.Media.Immutable
         /// <param name="opacity">The opacity of the brush.</param>
         /// <param name="spreadMethod">The spread method.</param>
         protected ImmutableGradientBrush(
-            IList<GradientStop> gradientStops,
+            IReadOnlyList<ImmutableGradientStop> gradientStops,
             double opacity,
             GradientSpreadMethod spreadMethod)
         {
@@ -28,14 +27,14 @@ namespace Avalonia.Media.Immutable
         /// Initializes a new instance of the <see cref="ImmutableGradientBrush"/> class.
         /// </summary>
         /// <param name="source">The brush from which this brush's properties should be copied.</param>
-        protected ImmutableGradientBrush(IGradientBrush source)
-            : this(source.GradientStops.ToList(), source.Opacity, source.SpreadMethod)
+        protected ImmutableGradientBrush(GradientBrush source)
+            : this(source.GradientStops.ToImmutable(), source.Opacity, source.SpreadMethod)
         {
 
         }
 
         /// <inheritdoc/>
-        public IList<GradientStop> GradientStops { get; }
+        public IReadOnlyList<IGradientStop> GradientStops { get; }
 
         /// <inheritdoc/>
         public double Opacity { get; }

src/Avalonia.Visuals/Media/Immutable/ImmutableGradientStop.cs

@@ -0,0 +1,20 @@
+namespace Avalonia.Media.Immutable
+{
+    /// <summary>
+    /// Describes the location and color of a transition point in a gradient.
+    /// </summary>
+    public class ImmutableGradientStop : IGradientStop
+    {
+        public ImmutableGradientStop(double offset, Color color)
+        {
+            Offset = offset;
+            Color = color;
+        }
+
+        /// <inheritdoc/>
+        public double Offset { get; }
+
+        /// <inheritdoc/>
+        public Color Color { get; }
+    }
+}

src/Avalonia.Visuals/Media/Immutable/ImmutableLinearGradientBrush.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Media.Immutable
         /// <param name="startPoint">The start point for the gradient.</param>
         /// <param name="endPoint">The end point for the gradient.</param>
         public ImmutableLinearGradientBrush(
-            IList<GradientStop> gradientStops,
+            IReadOnlyList<ImmutableGradientStop> gradientStops,
             double opacity = 1,
             GradientSpreadMethod spreadMethod = GradientSpreadMethod.Pad,
             RelativePoint? startPoint = null,
@@ -31,7 +31,7 @@ namespace Avalonia.Media.Immutable
         /// Initializes a new instance of the <see cref="ImmutableLinearGradientBrush"/> class.
         /// </summary>
         /// <param name="source">The brush from which this brush's properties should be copied.</param>
-        public ImmutableLinearGradientBrush(ILinearGradientBrush source)
+        public ImmutableLinearGradientBrush(LinearGradientBrush source)
             : base(source)
         {
             StartPoint = source.StartPoint;

src/Avalonia.Visuals/Media/Immutable/ImmutableRadialGradientBrush.cs

@@ -21,7 +21,7 @@ namespace Avalonia.Media.Immutable
         /// The horizontal and vertical radius of the outermost circle of the radial gradient.
         /// </param>
         public ImmutableRadialGradientBrush(
-            IList<GradientStop> gradientStops,
+            IReadOnlyList<ImmutableGradientStop> gradientStops,
             double opacity = 1,
             GradientSpreadMethod spreadMethod = GradientSpreadMethod.Pad,
             RelativePoint? center = null,
@@ -38,7 +38,7 @@ namespace Avalonia.Media.Immutable
         /// Initializes a new instance of the <see cref="ImmutableRadialGradientBrush"/> class.
         /// </summary>
         /// <param name="source">The brush from which this brush's properties should be copied.</param>
-        public ImmutableRadialGradientBrush(IRadialGradientBrush source)
+        public ImmutableRadialGradientBrush(RadialGradientBrush source)
             : base(source)
         {
             Center = source.Center;

src/Avalonia.Visuals/Media/LinearGradientBrush.cs

@@ -1,12 +1,14 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Media.Immutable;
+
 namespace Avalonia.Media
 {
     /// <summary>
     /// A brush that draws with a linear gradient.
     /// </summary>
-    public sealed class LinearGradientBrush : GradientBrush, ILinearGradientBrush, IMutableBrush
+    public sealed class LinearGradientBrush : GradientBrush, ILinearGradientBrush
     {
         /// <summary>
         /// Defines the <see cref="StartPoint"/> property.
@@ -24,6 +26,11 @@ namespace Avalonia.Media
                 nameof(EndPoint), 
                 RelativePoint.BottomRight);
 
+        static LinearGradientBrush()
+        {
+            AffectsRender<LinearGradientBrush>(StartPointProperty, EndPointProperty);
+        }
+
         /// <summary>
         /// Gets or sets the start point for the gradient.
         /// </summary>
@@ -43,9 +50,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        IBrush IMutableBrush.ToImmutable()
+        public override IBrush ToImmutable()
         {
-            return new Immutable.ImmutableLinearGradientBrush(this);
+            return new ImmutableLinearGradientBrush(this);
         }
     }
 }

src/Avalonia.Visuals/Media/RadialGradientBrush.cs

@@ -1,12 +1,14 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Media.Immutable;
+
 namespace Avalonia.Media
 {
     /// <summary>
     /// Paints an area with a radial gradient.
     /// </summary>
-    public sealed class RadialGradientBrush : GradientBrush, IRadialGradientBrush, IMutableBrush
+    public sealed class RadialGradientBrush : GradientBrush, IRadialGradientBrush
     {
         /// <summary>
         /// Defines the <see cref="Center"/> property.
@@ -63,9 +65,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        IBrush IMutableBrush.ToImmutable()
+        public override IBrush ToImmutable()
         {
-            return new Immutable.ImmutableRadialGradientBrush(this);
+            return new ImmutableRadialGradientBrush(this);
         }
     }
-}
+}

src/Avalonia.Visuals/Media/SolidColorBrush.cs

@@ -1,12 +1,14 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Media.Immutable;
+
 namespace Avalonia.Media
 {
     /// <summary>
     /// Fills an area with a solid color.
     /// </summary>
-    public class SolidColorBrush : Brush, ISolidColorBrush, IMutableBrush
+    public class SolidColorBrush : Brush, ISolidColorBrush
     {
         /// <summary>
         /// Defines the <see cref="Color"/> property.
@@ -14,6 +16,11 @@ namespace Avalonia.Media
         public static readonly StyledProperty<Color> ColorProperty =
             AvaloniaProperty.Register<SolidColorBrush, Color>(nameof(Color));
 
+        static SolidColorBrush()
+        {
+            AffectsRender<SolidColorBrush>(ColorProperty);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="SolidColorBrush"/> class.
         /// </summary>
@@ -75,9 +82,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        IBrush IMutableBrush.ToImmutable()
+        public override IBrush ToImmutable()
         {
-            return new Immutable.ImmutableSolidColorBrush(this);
+            return new ImmutableSolidColorBrush(this);
         }
     }
 }

src/Avalonia.Visuals/Media/TileBrush.cs

@@ -79,6 +79,13 @@ namespace Avalonia.Media
 
         static TileBrush()
         {
+            AffectsRender<TileBrush>(
+                AlignmentXProperty,
+                AlignmentYProperty,
+                DestinationRectProperty,
+                SourceRectProperty,
+                StretchProperty,
+                TileModeProperty);
             RenderOptions.BitmapInterpolationModeProperty.OverrideDefaultValue<TileBrush>(BitmapInterpolationMode.Default);
         }
 

src/Avalonia.Visuals/Media/VisualBrush.cs

@@ -1,6 +1,7 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using Avalonia.Media.Immutable;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Media
@@ -8,7 +9,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Paints an area with an <see cref="IVisual"/>.
     /// </summary>
-    public class VisualBrush : TileBrush, IVisualBrush, IMutableBrush
+    public class VisualBrush : TileBrush, IVisualBrush
     {
         /// <summary>
         /// Defines the <see cref="Visual"/> property.
@@ -16,6 +17,11 @@ namespace Avalonia.Media
         public static readonly StyledProperty<IVisual> VisualProperty =
             AvaloniaProperty.Register<VisualBrush, IVisual>(nameof(Visual));
 
+        static VisualBrush()
+        {
+            AffectsRender<VisualBrush>(VisualProperty);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="VisualBrush"/> class.
         /// </summary>
@@ -42,9 +48,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        IBrush IMutableBrush.ToImmutable()
+        public override IBrush ToImmutable()
         {
-            return new Immutable.ImmutableVisualBrush(this);
+            return new ImmutableVisualBrush(this);
         }
     }
 }

tests/Avalonia.RenderTests/Controls/CustomRenderTests.cs

@@ -124,7 +124,7 @@ namespace Avalonia.Direct2D1.RenderTests.Controls
                     {
                         StartPoint = new RelativePoint(0, 0, RelativeUnit.Relative),
                         EndPoint = new RelativePoint(1, 1, RelativeUnit.Relative),
-                        GradientStops = new[]
+                        GradientStops =
                         {
                             new GradientStop(Color.FromUInt32(0xffffffff), 0),
                             new GradientStop(Color.FromUInt32(0x00ffffff), 1)

tests/Avalonia.RenderTests/Media/LinearGradientBrushTests.cs

@@ -36,7 +36,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
                     {
                         StartPoint = new RelativePoint(0, 0.5, RelativeUnit.Relative),
                         EndPoint = new RelativePoint(1, 0.5, RelativeUnit.Relative),
-                        GradientStops = new[]
+                        GradientStops =
                         {
                             new GradientStop { Color = Colors.Red, Offset = 0 },
                             new GradientStop { Color = Colors.Blue, Offset = 1 }
@@ -63,7 +63,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
                     {
                         StartPoint = new RelativePoint(0.5, 0, RelativeUnit.Relative),
                         EndPoint = new RelativePoint(0.5, 1, RelativeUnit.Relative),
-                        GradientStops = new[]
+                        GradientStops =
                         {
                             new GradientStop { Color = Colors.Red, Offset = 0 },
                             new GradientStop { Color = Colors.Blue, Offset = 1 }

tests/Avalonia.RenderTests/Media/RadialGradientBrushTests.cs

@@ -34,7 +34,7 @@ namespace Avalonia.Direct2D1.RenderTests.Media
                 {
                     Background = new RadialGradientBrush
                     {
-                        GradientStops = new[]
+                        GradientStops =
                         {
                             new GradientStop { Color = Colors.Red, Offset = 0 },
                             new GradientStop { Color = Colors.Blue, Offset = 1 }

tests/Avalonia.RenderTests/OpacityMaskTests.cs

@@ -29,7 +29,7 @@ namespace Avalonia.Direct2D1.RenderTests
                 {
                     StartPoint = new RelativePoint(0, 0, RelativeUnit.Relative),
                     EndPoint = new RelativePoint(1, 1, RelativeUnit.Relative),
-                    GradientStops = new List<GradientStop>
+                    GradientStops =
                     {
                         new GradientStop(Color.FromUInt32(0xffffffff), 0),
                         new GradientStop(Color.FromUInt32(0x00ffffff), 1)
@@ -65,7 +65,7 @@ namespace Avalonia.Direct2D1.RenderTests
                 {
                     StartPoint = new RelativePoint(0, 0, RelativeUnit.Relative),
                     EndPoint = new RelativePoint(1, 1, RelativeUnit.Relative),
-                    GradientStops = new List<GradientStop>
+                    GradientStops =
                     {
                         new GradientStop(Color.FromUInt32(0xffffffff), 0),
                         new GradientStop(Color.FromUInt32(0x00ffffff), 1)

tests/Avalonia.Visuals.UnitTests/Media/ImageBrushTests.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Avalonia.Media;
+using Avalonia.Media.Imaging;
+using Moq;
+using Xunit;
+
+namespace Avalonia.Visuals.UnitTests.Media
+{
+    public class ImageBrushTests
+    {
+        [Fact]
+        public void Changing_Source_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new ImageBrush(bitmap1);
+            var raised = false;
+
+            target.Changed += (s, e) => raised = true;
+            target.Source = bitmap2;
+
+            Assert.True(raised);
+        }
+    }
+}

tests/Avalonia.Visuals.UnitTests/Media/LinearGradientBrushTests.cs

@@ -0,0 +1,86 @@
+using System;
+using Avalonia.Media;
+using Avalonia.Media.Imaging;
+using Moq;
+using Xunit;
+
+namespace Avalonia.Visuals.UnitTests.Media
+{
+    public class LinearGradientBrushTests
+    {
+        [Fact]
+        public void Changing_StartPoint_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new LinearGradientBrush();
+            var raised = false;
+
+            target.StartPoint = new RelativePoint();
+            target.Changed += (s, e) => raised = true;
+            target.StartPoint = new RelativePoint(10, 10, RelativeUnit.Absolute);
+
+            Assert.True(raised);
+        }
+
+        [Fact]
+        public void Changing_EndPoint_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new LinearGradientBrush();
+            var raised = false;
+
+            target.EndPoint = new RelativePoint();
+            target.Changed += (s, e) => raised = true;
+            target.EndPoint = new RelativePoint(10, 10, RelativeUnit.Absolute);
+
+            Assert.True(raised);
+        }
+
+        [Fact]
+        public void Changing_GradientStops_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new LinearGradientBrush();
+            var raised = false;
+
+            target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
+            target.Changed += (s, e) => raised = true;
+            target.GradientStops = new GradientStops { new GradientStop(Colors.Green, 0) };
+
+            Assert.True(raised);
+        }
+
+        [Fact]
+        public void Adding_GradientStop_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new LinearGradientBrush();
+            var raised = false;
+
+            target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
+            target.Changed += (s, e) => raised = true;
+            target.GradientStops.Add(new GradientStop(Colors.Green, 1));
+
+            Assert.True(raised);
+        }
+
+        [Fact]
+        public void Changing_GradientStop_Offset_Raises_Changed()
+        {
+            var bitmap1 = Mock.Of<IBitmap>();
+            var bitmap2 = Mock.Of<IBitmap>();
+            var target = new LinearGradientBrush();
+            var raised = false;
+
+            target.GradientStops = new GradientStops { new GradientStop(Colors.Red, 0) };
+            target.Changed += (s, e) => raised = true;
+            target.GradientStops[0].Offset = 0.5;
+
+            Assert.True(raised);
+        }
+    }
+}

tests/Avalonia.Visuals.UnitTests/Media/SolidColorBrushTests.cs

@@ -0,0 +1,21 @@
+using System;
+using Avalonia.Media;
+using Xunit;
+
+namespace Avalonia.Visuals.UnitTests.Media
+{
+    public class SolidColorBrushTests
+    {
+        [Fact]
+        public void Changing_Color_Raises_Changed()
+        {
+            var target = new SolidColorBrush(Colors.Red);
+            var raised = false;
+
+            target.Changed += (s, e) => raised = true;
+            target.Color = Colors.Green;
+
+            Assert.True(raised);
+        }
+    }
+}