Implement events for ToggleButton.

src/Avalonia.Controls/Primitives/ToggleButton.cs

@@ -7,8 +7,14 @@ using Avalonia.Data;
 
 namespace Avalonia.Controls.Primitives
 {
+    /// <summary>
+    /// Represents a control that a user can select (check) or clear (uncheck). Base class for controls that can switch states.
+    /// </summary>
     public class ToggleButton : Button
     {
+        /// <summary>
+        /// Defines the <see cref="IsChecked"/> property.
+        /// </summary>
         public static readonly DirectProperty<ToggleButton, bool?> IsCheckedProperty =
             AvaloniaProperty.RegisterDirect<ToggleButton, bool?>(
                 nameof(IsChecked),
@@ -17,9 +23,30 @@ namespace Avalonia.Controls.Primitives
                 unsetValue: null,
                 defaultBindingMode: BindingMode.TwoWay);
 
+        /// <summary>
+        /// Defines the <see cref="IsThreeState"/> property.
+        /// </summary>
         public static readonly StyledProperty<bool> IsThreeStateProperty =
             AvaloniaProperty.Register<ToggleButton, bool>(nameof(IsThreeState));
 
+        /// <summary>
+        /// Defines the <see cref="Checked"/> event.
+        /// </summary>
+        public static readonly RoutedEvent<RoutedEventArgs> CheckedEvent =
+            RoutedEvent.Register<ToggleButton, RoutedEventArgs>(nameof(Checked), RoutingStrategies.Bubble);
+
+        /// <summary>
+        /// Defines the <see cref="Unchecked"/> event.
+        /// </summary>
+        public static readonly RoutedEvent<RoutedEventArgs> UncheckedEvent =
+            RoutedEvent.Register<ToggleButton, RoutedEventArgs>(nameof(Unchecked), RoutingStrategies.Bubble);
+
+        /// <summary>
+        /// Defines the <see cref="Unchecked"/> event.
+        /// </summary>
+        public static readonly RoutedEvent<RoutedEventArgs> IndeterminateEvent =
+            RoutedEvent.Register<ToggleButton, RoutedEventArgs>(nameof(Indeterminate), RoutingStrategies.Bubble);
+
         private bool? _isChecked = false;
 
         static ToggleButton()
@@ -27,14 +54,49 @@ namespace Avalonia.Controls.Primitives
             PseudoClass<ToggleButton, bool?>(IsCheckedProperty, c => c == true, ":checked");
             PseudoClass<ToggleButton, bool?>(IsCheckedProperty, c => c == false, ":unchecked");
             PseudoClass<ToggleButton, bool?>(IsCheckedProperty, c => c == null, ":indeterminate");
+
+            IsCheckedProperty.Changed.AddClassHandler<ToggleButton>((x, e) => x.OnIsCheckedChanged(e));
+        }
+
+        /// <summary>
+        /// Raised when a <see cref="ToggleButton"/> is checked.
+        /// </summary>
+        public event EventHandler<RoutedEventArgs> Checked
+        {
+            add { AddHandler(CheckedEvent, value); }
+            remove { RemoveHandler(CheckedEvent, value); }
+        }
+
+        /// <summary>
+        /// Raised when a <see cref="ToggleButton"/> is unchecked.
+        /// </summary>
+        public event EventHandler<RoutedEventArgs> Unchecked
+        {
+            add { AddHandler(UncheckedEvent, value); }
+            remove { RemoveHandler(UncheckedEvent, value); }
+        }
+
+        /// <summary>
+        /// Raised when a <see cref="ToggleButton"/> is neither checked nor unchecked.
+        /// </summary>
+        public event EventHandler<RoutedEventArgs> Indeterminate
+        {
+            add { AddHandler(IndeterminateEvent, value); }
+            remove { RemoveHandler(IndeterminateEvent, value); }
         }
 
+        /// <summary>
+        /// Gets or sets whether the <see cref="ToggleButton"/> is checked.
+        /// </summary>
         public bool? IsChecked
         {
             get { return _isChecked; }
             set { SetAndRaise(IsCheckedProperty, ref _isChecked, value); }
         }
 
+        /// <summary>
+        /// Gets or sets a value that indicates whether the control supports three states.
+        /// </summary>
         public bool IsThreeState
         {
             get => GetValue(IsThreeStateProperty);
@@ -47,18 +109,78 @@ namespace Avalonia.Controls.Primitives
             base.OnClick();
         }
 
+        /// <summary>
+        /// Toggles the <see cref="IsChecked"/> property.
+        /// </summary>
         protected virtual void Toggle()
         {
             if (IsChecked.HasValue)
+            {
                 if (IsChecked.Value)
+                {
                     if (IsThreeState)
+                    {
                         IsChecked = null;
+                    }
                     else
+                    {
                         IsChecked = false;
+                    }
+                }
                 else
+                {
                     IsChecked = true;
+                }
+            }
             else
+            {
                 IsChecked = false;
+            }
+        }
+
+        /// <summary>
+        /// Called when <see cref="IsChecked"/> becomes true.
+        /// </summary>
+        /// <param name="e">Event arguments for the routed event that is raised by the default implementation of this method.</param>
+        protected virtual void OnChecked(RoutedEventArgs e)
+        {
+            RaiseEvent(e);
+        }
+
+        /// <summary>
+        /// Called when <see cref="IsChecked"/> becomes false.
+        /// </summary>
+        /// <param name="e">Event arguments for the routed event that is raised by the default implementation of this method.</param>
+        protected virtual void OnUnchecked(RoutedEventArgs e)
+        {
+            RaiseEvent(e);
+        }
+
+        /// <summary>
+        /// Called when <see cref="IsChecked"/> becomes null.
+        /// </summary>
+        /// <param name="e">Event arguments for the routed event that is raised by the default implementation of this method.</param>
+        protected virtual void OnIndeterminate(RoutedEventArgs e)
+        {
+            RaiseEvent(e);
+        }
+
+        private void OnIsCheckedChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            var newValue = (bool?)e.NewValue;
+
+            switch (newValue)
+            {
+                case true:
+                    OnChecked(new RoutedEventArgs(CheckedEvent));
+                    break;
+                case false:
+                    OnUnchecked(new RoutedEventArgs(UncheckedEvent));
+                    break;
+                default:
+                    OnIndeterminate(new RoutedEventArgs(IndeterminateEvent));
+                    break;
+            }
         }
     }
 }

tests/Avalonia.Controls.UnitTests/Primitives/ToggleButtonTests.cs

@@ -1,5 +1,4 @@
 using Avalonia.Data;
-using Avalonia.Markup.Data;
 using Avalonia.UnitTests;
 
 using Xunit;
@@ -63,6 +62,54 @@ namespace Avalonia.Controls.Primitives.UnitTests
             Assert.Null(threeStateButton.IsChecked);
         }
 
+        [Fact]
+        public void ToggleButton_Events_Are_Raised_On_Is_Checked_Changes()
+        {
+            var threeStateButton = new ToggleButton();
+
+            bool checkedRaised = false;
+            threeStateButton.Checked += (_, __) => checkedRaised = true;
+
+            threeStateButton.IsChecked = true;
+            Assert.True(checkedRaised);
+
+            bool uncheckedRaised = false;
+            threeStateButton.Unchecked += (_, __) => uncheckedRaised = true;
+
+            threeStateButton.IsChecked = false;
+            Assert.True(uncheckedRaised);
+
+            bool indeterminateRaised = false;
+            threeStateButton.Indeterminate += (_, __) => indeterminateRaised = true;
+
+            threeStateButton.IsChecked = null;
+            Assert.True(indeterminateRaised);
+        }
+
+        [Fact]
+        public void ToggleButton_Events_Are_Raised_When_Toggling()
+        {
+            var threeStateButton = new TestToggleButton { IsThreeState = true };
+
+            bool checkedRaised = false;
+            threeStateButton.Checked += (_, __) => checkedRaised = true;
+
+            threeStateButton.Toggle();
+            Assert.True(checkedRaised);
+
+            bool indeterminateRaised = false;
+            threeStateButton.Indeterminate += (_, __) => indeterminateRaised = true;
+
+            threeStateButton.Toggle();
+            Assert.True(indeterminateRaised);
+
+            bool uncheckedRaised = false;
+            threeStateButton.Unchecked += (_, __) => uncheckedRaised = true;
+
+            threeStateButton.Toggle();
+            Assert.True(uncheckedRaised);
+        }
+
         private class Class1 : NotifyingBase
         {
             private bool _foo;
@@ -80,5 +127,10 @@ namespace Avalonia.Controls.Primitives.UnitTests
                 set { nullableFoo = value; RaisePropertyChanged(); }
             }
         }
+
+        private class TestToggleButton : ToggleButton
+        {
+            public new void Toggle() => base.Toggle();
+        }
     }
 }