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[controls] one less WeakReference in TypedBinding #13304

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Feb 14, 2023
Merged

[controls] one less WeakReference in TypedBinding #13304

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19 changes: 9 additions & 10 deletions src/Controls/src/Core/TypedBinding.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -249,29 +249,28 @@ class PropertyChangedProxy
public Func<TSource, object> PartGetter { get; }
public string PropertyName { get; }
public BindingExpression.WeakPropertyChangedProxy Listener { get; }
WeakReference<INotifyPropertyChanged> _weakPart = new WeakReference<INotifyPropertyChanged>(null);
readonly BindingBase _binding;
PropertyChangedEventHandler handler;
public INotifyPropertyChanged Part
{
get
{
INotifyPropertyChanged target;
if (_weakPart.TryGetTarget(out target))
if (Listener != null && Listener.Source.TryGetTarget(out var target))
return target;
return null;
}
set
{
if (Listener != null && Listener.Source.TryGetTarget(out var source) && ReferenceEquals(value, source))
if (Listener != null)
{
//Already subscribed
return;

//clear out previous subscription
Listener?.Unsubscribe();
if (Listener.Source.TryGetTarget(out var source) && ReferenceEquals(value, source))
return;

_weakPart.SetTarget(value);
Listener.SubscribeTo(value, handler);
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This line actually looked like it could throw NRE before?

//clear out previous subscription
Listener.Unsubscribe();
Listener.SubscribeTo(value, handler);
}
}
}

Expand Down
42 changes: 33 additions & 9 deletions src/Controls/tests/Core.UnitTests/TypedBindingUnitTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Globalization;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using Microsoft.Maui.Controls.Internals;
using Xunit;
using Xunit.Sdk;
Expand Down Expand Up @@ -1376,7 +1377,20 @@ event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
remove { PropertyChanged -= value; }
}

public string Foo { get; set; }
string _foo;

public string Foo
{
get => _foo;
set
{
if (_foo != value)
{
_foo = value;
OnPropertyChanged(nameof(Foo));
}
}
}

public int InvocationListSize()
{
Expand All @@ -1392,9 +1406,10 @@ public virtual void OnPropertyChanged([CallerMemberName] string propertyName = n
}

[Fact]
public void BindingUnsubscribesForDeadTarget()
public async Task BindingUnsubscribesForDeadTarget()
{
var viewmodel = new TestViewModel();
WeakReference bindingRef = null, buttonRef = null;

int i = 0;
Action create = null;
Expand All @@ -1407,30 +1422,37 @@ public void BindingUnsubscribesForDeadTarget()
}

var button = new Button();
button.SetBinding(Button.TextProperty, new TypedBinding<TestViewModel, string>(vm => (vm.Foo, true), (vm, s) => vm.Foo = s, new[] {
var binding = new TypedBinding<TestViewModel, string>(vm => (vm.Foo, true), (vm, s) => vm.Foo = s, new[] {
new Tuple<Func<TestViewModel, object>, string>(vm=>vm,"Foo")
}));
});
button.SetBinding(Button.TextProperty, binding);
button.BindingContext = viewmodel;
bindingRef = new WeakReference(binding);
buttonRef = new WeakReference(button);
};

create();
Assert.Equal(viewmodel.Foo = "Bar", ((Button)buttonRef.Target).Text);

Assert.Equal(1, viewmodel.InvocationListSize());

await Task.Yield();
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

viewmodel.OnPropertyChanged("Foo");

Assert.Equal(0, viewmodel.InvocationListSize());

Assert.False(bindingRef.IsAlive, "Binding should not be alive!");
Assert.False(buttonRef.IsAlive, "Button should not be alive!");
}

[Fact]
public void BindingDoesNotStayAliveForDeadTarget()
public async Task BindingDoesNotStayAliveForDeadTarget()
{
var viewModel = new TestViewModel();
WeakReference bindingRef = null;
WeakReference bindingRef = null, buttonRef = null;

int i = 0;
Action create = null;
Expand All @@ -1450,18 +1472,20 @@ public void BindingDoesNotStayAliveForDeadTarget()
button.BindingContext = viewModel;

bindingRef = new WeakReference(binding);
binding = null;
buttonRef = new WeakReference(button);
};

create();
Assert.Equal(viewModel.Foo = "Bar", ((Button)buttonRef.Target).Text);

Assert.Equal(1, viewModel.InvocationListSize());

await Task.Yield();
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();

Assert.False(bindingRef.IsAlive, "Binding should not be alive!");
Assert.False(buttonRef.IsAlive, "Button should not be alive!");
}

[Fact]
Expand Down