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Merge pull request #2644 from joerih/fix-event-handler-leak-in-proper…
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…ty-binding

Fix an event handler leak in `Binding.RemovePropertyEvent`
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cwensley authored Sep 16, 2024
2 parents 4451ef7 + e79a63b commit 7f71c1d
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Showing 5 changed files with 341 additions and 19 deletions.
108 changes: 94 additions & 14 deletions src/Eto/Forms/Binding/Binding.helpers.cs
Original file line number Diff line number Diff line change
Expand Up @@ -189,12 +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>
/// <seealso cref="RemovePropertyEvent"/>
/// <seealso cref="RemovePropertyEvent(object,EventHandler{EventArgs})"/>
/// <seealso cref="RemovePropertyEvent(object,string,EventHandler{EventArgs})"/>
public static void AddPropertyEvent(object obj, string propertyName, EventHandler<EventArgs> eh)
{
var notifyObject = obj as INotifyPropertyChanged;
if (notifyObject != null)
new PropertyNotifyHelper(notifyObject, propertyName).Changed += eh;
if (obj is INotifyPropertyChanged notifyObject)
{
var helper = new PropertyNotifyHelper(notifyObject, propertyName);
helper.Changed += eh;
}
}

/// <summary>
Expand All @@ -208,32 +211,109 @@ public static void AddPropertyEvent(object obj, string propertyName, EventHandle
/// <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>
/// <seealso cref="RemovePropertyEvent"/>
/// <seealso cref="RemovePropertyEvent(object,EventHandler{EventArgs})"/>
/// <seealso cref="RemovePropertyEvent{T,TProperty}(T,Expression{Func{T, TProperty}},EventHandler{EventArgs})"/>
public static void AddPropertyEvent<T, TProperty>(T obj, Expression<Func<T, TProperty>> propertyExpression, EventHandler<EventArgs> eh)
{
var notifyObject = obj as INotifyPropertyChanged;
if (notifyObject != null)
var propertyInfo = propertyExpression.GetMemberInfo();
if (propertyInfo != null)
{
var propertyInfo = propertyExpression.GetMemberInfo();
if (propertyInfo != null)
new PropertyNotifyHelper(notifyObject, propertyInfo.Member.Name).Changed += eh;
AddPropertyEvent(obj, propertyInfo.Member.Name, eh);
}
}

/// <summary>
/// Removes an event handler previously attached with the AddPropertyEvent method.
/// </summary>
/// <param name="obj">INotifyPropertyChanged object to remove the event handler from</param>
/// <remarks>
/// 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 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)
{
var helper = eh.Target as PropertyNotifyHelper;
if (helper != null)
if (obj is PropertyNotifyHelper helper)
{
helper.Changed -= eh;
helper.Unregister(obj);
}
else if (obj is INotifyPropertyChanged notifyObject)
{
var propertyChangedField = GetPropertyChangedField(notifyObject);
if (propertyChangedField == null)
return;

var propertyChangedDelegates = ((Delegate)propertyChangedField.GetValue(notifyObject))?.GetInvocationList().OfType<PropertyChangedEventHandler>() ?? Enumerable.Empty<PropertyChangedEventHandler>();
foreach (var del in propertyChangedDelegates)
{
// find ones hooked up to the PropertyNotifyHelper, regardless of property
if (del.Target is PropertyNotifyHelper h && h.IsHookedTo(eh))
{
h.Changed -= eh;
h.Unregister(obj);
}
}
}
}

/// <summary>
/// Removes an event handler previously attached with the AddPropertyEvent method.
/// </summary>
/// <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})"/>
public static void RemovePropertyEvent<T, TProperty>(T obj, Expression<Func<T, TProperty>> propertyExpression, EventHandler<EventArgs> eh)
{
var propertyInfo = propertyExpression.GetMemberInfo();
if (propertyInfo != null)
{
RemovePropertyEvent(obj, propertyInfo.Member.Name, eh);
}
}

/// <summary>
/// Removes an event handler previously attached with the AddPropertyEvent method.
/// </summary>
/// <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})"/>
public static void RemovePropertyEvent(object obj, string propertyName, EventHandler<EventArgs> eh)
{
if (obj is INotifyPropertyChanged notifyObject)
{
// this only works when PropertyChanged is a simple public event
// if it is implemented explicitly via the interface this won't work
var propertyChangedField = GetPropertyChangedField(notifyObject);
if (propertyChangedField == null)
return;

var propertyChangedDelegates = ((Delegate)propertyChangedField.GetValue(notifyObject))?.GetInvocationList().OfType<PropertyChangedEventHandler>() ?? Enumerable.Empty<PropertyChangedEventHandler>();
foreach (var del in propertyChangedDelegates)
{
// find ones hooked up to the PropertyNotifyHelper
if (del.Target is PropertyNotifyHelper h && h.PropertyName == propertyName && h.IsHookedTo(eh))
{
h.Changed -= eh;
h.Unregister(obj);
}
}
}
}

static FieldInfo GetPropertyChangedField(object obj)
{
FieldInfo field = null;
var type = obj?.GetType();
while (field == null && type != null)
{
field = type.GetField(nameof(INotifyPropertyChanged.PropertyChanged), BindingFlags.Instance | BindingFlags.NonPublic);
type = type.BaseType;
}
return field;
}

/// <summary>
Expand Down Expand Up @@ -289,4 +369,4 @@ public static void ExecuteCommand<T>(object dataContext, Expression<Func<T, ICom
{
ExecuteCommand(dataContext, Binding.Property(commandExpression), parameter);
}
}
}
5 changes: 3 additions & 2 deletions src/Eto/Forms/Binding/DelegateBinding.cs
Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
}

Expand Down
17 changes: 14 additions & 3 deletions src/Eto/Forms/Binding/PropertyNotifyHelper.cs
Original file line number Diff line number Diff line change
Expand Up @@ -4,15 +4,15 @@ namespace Eto.Forms;
/// Helper to turn a property changed event to an EventHandler for binding
/// </summary>
/// <remarks>
/// Use <see cref="Binding.AddPropertyEvent"/> and <see cref="Binding.RemovePropertyEvent"/> to access
/// this functionality.
/// Use <see cref="Binding.AddPropertyEvent"/> and <see cref="Binding.RemovePropertyEvent(object,string,EventHandler{EventArgs})"/> to access
/// this functionality, or better yet use the <see cref="PropertyBinding{T}"/> class.
/// </remarks>
class PropertyNotifyHelper
{
public string PropertyName { get; private set; }

public event EventHandler<EventArgs> Changed;

public PropertyNotifyHelper(INotifyPropertyChanged obj, string propertyName)
{
PropertyName = propertyName;
Expand All @@ -35,4 +35,15 @@ void obj_PropertyChanged(object sender, PropertyChangedEventArgs e)
}
}

public bool IsHookedTo(EventHandler<EventArgs> eh)
{
foreach (var invocation in Changed.GetInvocationList())
{
if (invocation == (Delegate)eh)
{
return true;
}
}
return false;
}
}
197 changes: 197 additions & 0 deletions test/Eto.Test/UnitTests/Forms/Bindings/BindingHelpersTests.cs
Original file line number Diff line number Diff line change
@@ -0,0 +1,197 @@
using NUnit.Framework;

namespace Eto.Test.UnitTests.Forms.Bindings;

[TestFixture]
public class BindingHelpersTests
{
[Test]
public void AddingAPropertyEventByNameShouldWork()
{
var propertyValueChanged = false;
void Handler(object sender, EventArgs e) => propertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true };
Binding.AddPropertyEvent(bindObject, "BoolProperty", Handler);

// Act
bindObject.BoolProperty = false;

// Assert
Assert.That(propertyValueChanged, Is.True);
}

[Test]
public void AddingAPropertyEventByExpressionShouldWork()
{
var propertyValueChanged = false;
void Handler(object sender, EventArgs e) => propertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);

// Act
bindObject.BoolProperty = false;

// Assert
Assert.That(propertyValueChanged, Is.True);
}

[Test]
public void AddingMultiplePropertyEventsShouldWork()
{
var boolPropertyValueChanged = false;
var intPropertyValueChanged = false;
var stringPropertyValueChanged = false;
void BoolHandler(object sender, EventArgs e) => boolPropertyValueChanged = true;
void IntHandler(object sender, EventArgs e) => intPropertyValueChanged = true;
void StringHandler(object sender, EventArgs e) => stringPropertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, BoolHandler);
Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, IntHandler);
Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, StringHandler);

// Act
bindObject.BoolProperty = false;
bindObject.IntProperty = 4;
bindObject.StringProperty = "Test2";

// Assert
Assert.That(boolPropertyValueChanged, Is.True);
Assert.That(intPropertyValueChanged, Is.True);
Assert.That(stringPropertyValueChanged, Is.True);
}

[Test]
public void APropertyEventShouldNotRespondToADifferentProperty()
{
var propertyValueChanged = false;
void Handler(object sender, EventArgs e) => propertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 1 };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);

// Act
bindObject.IntProperty = 2;

// Assert
Assert.That(propertyValueChanged, Is.False);
}

[Test]
public void RemovingAPropertyEventShouldWork()
{
var propertyValueChanged = false;
void Handler(object sender, EventArgs e) => propertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);

// Act
Binding.RemovePropertyEvent(bindObject, Handler);
bindObject.BoolProperty = false;

// Assert
Assert.That(propertyValueChanged, Is.False);
}

[Test]
public void RemovingAPropertyEventShouldKeepOtherEvents()
{
var boolPropertyValueChanged = false;
var intPropertyValueChanged = false;
var stringPropertyValueChanged = false;
void BoolHandler(object sender, EventArgs e) => boolPropertyValueChanged = true;
void IntHandler(object sender, EventArgs e) => intPropertyValueChanged = true;
void StringHandler(object sender, EventArgs e) => stringPropertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
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);
bindObject.BoolProperty = false;
bindObject.IntProperty = 4;
bindObject.StringProperty = "Test2";

// Assert
Assert.That(boolPropertyValueChanged, Is.True);
Assert.That(intPropertyValueChanged, Is.False);
Assert.That(stringPropertyValueChanged, Is.True);
}

[Test]
public void RemovingAllPropertyEventsShouldWork()
{
var boolPropertyValueChanged = false;
var intPropertyValueChanged = false;
var stringPropertyValueChanged = false;
void BoolHandler(object sender, EventArgs e) => boolPropertyValueChanged = true;
void IntHandler(object sender, EventArgs e) => intPropertyValueChanged = true;
void StringHandler(object sender, EventArgs e) => stringPropertyValueChanged = true;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
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);
Binding.RemovePropertyEvent(bindObject, BoolHandler);
Binding.RemovePropertyEvent(bindObject, IntHandler);
bindObject.BoolProperty = false;
bindObject.IntProperty = 4;
bindObject.StringProperty = "Test2";

// Assert
Assert.That(boolPropertyValueChanged, Is.False);
Assert.That(intPropertyValueChanged, Is.False);
Assert.That(stringPropertyValueChanged, Is.False);
}

[Test]
public void UnsubscribingToSameEventShouldntUnsubscribeAllWhenPassingProperty()
{
var numchanged = 0;
void Handler(object sender, EventArgs e) => numchanged++;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);
Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, Handler);
Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, Handler);

// Act
Binding.RemovePropertyEvent(bindObject, obj => obj.BoolProperty, Handler);
bindObject.BoolProperty = false;
bindObject.IntProperty = 4;
bindObject.StringProperty = "Test2";

// Assert
Assert.That(numchanged, Is.EqualTo(2));
}

[Test]
public void UnsubscribingToSameEventWillUnsubscribeAll()
{
var numchanged = 0;
void Handler(object sender, EventArgs e) => numchanged++;

var bindObject = new BindObject { BoolProperty = true, IntProperty = 3, StringProperty = "Test1" };
Binding.AddPropertyEvent(bindObject, obj => obj.BoolProperty, Handler);
Binding.AddPropertyEvent(bindObject, obj => obj.IntProperty, Handler);
Binding.AddPropertyEvent(bindObject, obj => obj.StringProperty, Handler);

// Act
Binding.RemovePropertyEvent(bindObject, Handler);
bindObject.BoolProperty = false;
bindObject.IntProperty = 4;
bindObject.StringProperty = "Test2";

// Assert
// ambiguous which one to remove, so it removed all -- need to specify property or return value from AddPropertyEvent
Assert.That(numchanged, Is.EqualTo(0));
}
}
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