Fix breaking ABI changes

- return for AddPropertyEvent is now void like before to avoid ABI breaks
- Use PropertyBinding to wire up property events in DelegateBinding so it supports both INotifyPropertyChanged and MyPropertyChanged events

src/Eto/Forms/Binding/Binding.helpers.cs

@@ -189,18 +189,15 @@ public static IndirectBinding<TValue> Property<TValue>(string propertyName, bool
 	/// <param name="obj">INotifyPropertyChanged object to attach the event handler to</param>
 	/// <param name="propertyName">Name of the property to trigger the changed event.</param>
 	/// <param name="eh">Event handler delegate to trigger when the specified property changes</param>
-	/// <returns>Object to pass to RemovePropertyEvent to unregister the event</returns>
 	/// <seealso cref="RemovePropertyEvent(object,EventHandler{EventArgs})"/>
 	/// <seealso cref="RemovePropertyEvent(object,string,EventHandler{EventArgs})"/>
-	public static object AddPropertyEvent(object obj, string propertyName, EventHandler<EventArgs> eh)
+	public static void AddPropertyEvent(object obj, string propertyName, EventHandler<EventArgs> eh)
 	{
 		if (obj is INotifyPropertyChanged notifyObject)
 		{
 			var helper = new PropertyNotifyHelper(notifyObject, propertyName);
 			helper.Changed += eh;
-			return helper;
 		}
-		return null;
 	}
 
 	/// <summary>
@@ -214,27 +211,25 @@ public static object AddPropertyEvent(object obj, string propertyName, EventHand
 	/// <param name="obj">INotifyPropertyChanged object to attach the event handler to</param>
 	/// <param name="propertyExpression">Expression to the property to trigger the changed event.</param>
 	/// <param name="eh">Event handler delegate to trigger when the specified property changes</param>
-	/// <returns>Object to pass to RemovePropertyEvent to unregister the event</returns>
 	/// <seealso cref="RemovePropertyEvent(object,EventHandler{EventArgs})"/>
 	/// <seealso cref="RemovePropertyEvent{T,TProperty}(T,Expression{Func{T, TProperty}},EventHandler{EventArgs})"/>
-	public static object AddPropertyEvent<T, TProperty>(T obj, Expression<Func<T, TProperty>> propertyExpression, EventHandler<EventArgs> eh)
+	public static void AddPropertyEvent<T, TProperty>(T obj, Expression<Func<T, TProperty>> propertyExpression, EventHandler<EventArgs> eh)
 	{
 		var propertyInfo = propertyExpression.GetMemberInfo();
 		if (propertyInfo != null)
 		{
-			return AddPropertyEvent(obj, propertyInfo.Member.Name, eh);
+			AddPropertyEvent(obj, propertyInfo.Member.Name, eh);
 		}
-		return null;
 	}
 
 	/// <summary>
 	/// Removes an event handler previously attached with the AddPropertyEvent method.
 	/// </summary>
 	/// <remarks>
-	/// Note that if you pass the object that the event is attached to instea of the object returned from AddPropertyEvent,
-	/// then this will unsubscribe from all property handlers that point to the same delegate specified by <paramref name="eh"/>
+	/// Note that this will unsubscribe from all property handlers that point to the same delegate specified by <paramref name="eh"/>.
+	/// Use <see cref="RemovePropertyEvent(object, string, EventHandler{EventArgs})"/> to only unsubscribe for a single property.
 	/// </remarks>
-	/// <param name="obj">Object returned from AddPropertyEvent to unsubscribe, or the object the event is subscribed to</param>
+	/// <param name="obj">Object the event is subscribed to</param>
 	/// <param name="eh">Event handler delegate to remove</param>
 	/// <seealso cref="AddPropertyEvent(object,string,EventHandler{EventArgs})"/>
 	public static void RemovePropertyEvent(object obj, EventHandler<EventArgs> eh)
@@ -266,7 +261,7 @@ public static void RemovePropertyEvent(object obj, EventHandler<EventArgs> eh)
 	/// <summary>
 	/// Removes an event handler previously attached with the AddPropertyEvent method.
 	/// </summary>
-	/// <param name="obj">Object returned from AddPropertyEvent to unsubscribe</param>
+	/// <param name="obj">INotifyPropertyChanged object to unsubscribe from</param>
 	/// <param name="propertyExpression">Expression for the property to remove the event handler for</param>
 	/// <param name="eh">Event handler delegate to remove</param>
 	/// <seealso cref="AddPropertyEvent{T,TProperty}(T,Expression{Func{T, TProperty}},EventHandler{EventArgs})"/>
@@ -282,7 +277,7 @@ public static void RemovePropertyEvent<T, TProperty>(T obj, Expression<Func<T, T
 	/// <summary>
 	/// Removes an event handler previously attached with the AddPropertyEvent method.
 	/// </summary>
-	/// <param name="obj">Object returned from AddPropertyEvent to unsubscribe</param>
+	/// <param name="obj">INotifyPropertyChanged object to unsubscribe from</param>
 	/// <param name="propertyName">Name of the property to remove the event handler for</param>
 	/// <param name="eh">Event handler delegate to remove</param>
 	/// <seealso cref="AddPropertyEvent(object,string,EventHandler{EventArgs})"/>

src/Eto/Forms/Binding/DelegateBinding.cs

@@ -221,8 +221,9 @@ public class DelegateBinding<T, TValue> : IndirectBinding<TValue>
 		DefaultSetValue = defaultSetValue;
 		if (!string.IsNullOrEmpty(notifyProperty))
 		{
-			AddChangeEvent = (obj, eh) => { AddPropertyEvent(obj, notifyProperty, eh); return obj; };
-			RemoveChangeEvent = (obj, eh) => RemovePropertyEvent(obj, eh);
+			var binding = new PropertyBinding<object>(notifyProperty);
+			AddChangeEvent = (obj, eh) => binding.AddValueChangedHandler(obj, eh);
+			RemoveChangeEvent = (obj, eh) => binding.RemoveValueChangedHandler(obj, eh);
 		}
 	}
 

src/Eto/Forms/Binding/PropertyNotifyHelper.cs

@@ -5,7 +5,7 @@ namespace Eto.Forms;
 /// </summary>
 /// <remarks>
 /// Use <see cref="Binding.AddPropertyEvent"/> and <see cref="Binding.RemovePropertyEvent(object,string,EventHandler{EventArgs})"/> to access
-/// this functionality.
+/// this functionality, or better yet use the <see cref="PropertyBinding{T}"/> class.
 /// </remarks>
 class PropertyNotifyHelper
 {

test/Eto.Test/UnitTests/Forms/Bindings/BindingHelpersTests.cs

@@ -86,7 +86,7 @@ public void RemovingAPropertyEventShouldWork()
 		void Handler(object sender, EventArgs e) => propertyValueChanged = true;
 
 		var bindObject = new BindObject { BoolProperty = true };
-		var obj = Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);
 
 		// Act
 		Binding.RemovePropertyEvent(bindObject, Handler);
@@ -107,9 +107,9 @@ public void RemovingAPropertyEventShouldKeepOtherEvents()
 		void StringHandler(object sender, EventArgs e) => stringPropertyValueChanged = true;
 
 		var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
-		var boolObj = Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, BoolHandler);
-		var intObj = Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, IntHandler);
-		var stringObj = Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, StringHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, BoolHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, IntHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, StringHandler);
 
 		// Act
 		Binding.RemovePropertyEvent(bindObject, IntHandler);
@@ -134,9 +134,9 @@ public void RemovingAllPropertyEventsShouldWork()
 		void StringHandler(object sender, EventArgs e) => stringPropertyValueChanged = true;
 
 		var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
-		var boolObj = Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, BoolHandler);
-		var intObj = Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, IntHandler);
-		var stringObj = Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, StringHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, BoolHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, IntHandler);
+		Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, StringHandler);
 
 		// Act
 		Binding.RemovePropertyEvent(bindObject, StringHandler);