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Add BindingOperations.GetBindingExpressionBase. (#16214)
With basic unit tests. Co-authored-by: Max Katz <[email protected]>
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‎src/Avalonia.Base/Data/BindingOperations.cs

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@@ -101,6 +101,25 @@ public static IDisposable Apply(
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return Apply(target, property, binding);
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}
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/// <summary>
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/// Retrieves the <see cref="BindingExpressionBase"/> that is currently active on the
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/// specified property.
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/// </summary>
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/// <param name="target">
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/// The <see cref="AvaloniaObject"/> from which to retrieve the binding expression.
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/// </param>
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/// <param name="property">
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/// The binding target property from which to retrieve the binding expression.
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/// </param>
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/// <returns>
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/// The <see cref="BindingExpressionBase"/> object that is active on the given property or
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/// null if no binding expression is active on the given property.
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/// </returns>
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public static BindingExpressionBase? GetBindingExpressionBase(AvaloniaObject target, AvaloniaProperty property)
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{
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return target.GetValueStore().GetExpression(property);
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}
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private sealed class TwoWayBindingDisposable : IDisposable
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{
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private readonly IDisposable _toTargetSubscription;

‎src/Avalonia.Base/PropertyStore/ValueStore.cs

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@@ -292,6 +292,42 @@ public T GetValue<T>(StyledProperty<T> property)
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return property.GetDefaultValue(Owner);
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}
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public BindingExpressionBase? GetExpression(AvaloniaProperty property)
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{
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var evaluatedLocalValue = false;
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bool TryGetLocalValue(out BindingExpressionBase? result)
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{
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if (!evaluatedLocalValue)
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{
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evaluatedLocalValue = true;
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if (_localValueBindings?.TryGetValue(property.Id, out var o) == true)
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{
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result = o as BindingExpressionBase;
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return true;
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}
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}
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result = null;
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return false;
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}
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for (var i = _frames.Count - 1; i >= 0; --i)
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{
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var frame = _frames[i];
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if (frame.Priority > BindingPriority.LocalValue && TryGetLocalValue(out var localExpression))
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return localExpression;
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if (frame.TryGetEntryIfActive(property, out var entry, out _))
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return entry as BindingExpressionBase;
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}
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TryGetLocalValue(out var e);
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return e;
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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private static EffectiveValue<T> CastEffectiveValue<T>(EffectiveValue value)
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{

‎tests/Avalonia.Base.UnitTests/Data/BindingOperationsTests.cs

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using Avalonia.Controls;
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using Avalonia.Data;
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using Avalonia.Data.Converters;
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using Avalonia.Styling;
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using Avalonia.UnitTests;
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using Xunit;
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namespace Avalonia.Base.UnitTests.Data;
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public class BindingOperationsTests
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{
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[Fact]
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public void GetBindingExpressionBase_Returns_Null_When_Not_Bound()
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{
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var target = new Control();
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.Null(expression);
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}
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[Theory]
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[InlineData(BindingPriority.Animation)]
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[InlineData(BindingPriority.LocalValue)]
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[InlineData(BindingPriority.Style)]
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[InlineData(BindingPriority.StyleTrigger)]
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public void GetBindingExpressionBase_Returns_Expression_When_Bound(BindingPriority priority)
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{
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var data = new { Tag = "foo" };
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var target = new Control { DataContext = data };
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var binding = new Binding("Tag") { Priority = priority };
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target.Bind(Control.TagProperty, binding);
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Expression_When_Bound_Locally_With_Binding_Error()
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{
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// Target has no data context so binding will fail.
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var target = new Control();
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var binding = new Binding("Tag");
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target.Bind(Control.TagProperty, binding);
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Expression_When_Bound_To_MultiBinding()
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{
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var data = new { Tag = "foo" };
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var target = new Control { DataContext = data };
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var binding = new MultiBinding
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{
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Converter = new FuncMultiValueConverter<object, string>(x => string.Join(',', x)),
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Bindings =
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{
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new Binding("Tag"),
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new Binding("Tag"),
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}
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};
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target.Bind(Control.TagProperty, binding);
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Binding_When_Bound_Via_ControlTheme()
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{
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var target = new Control();
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var binding = new Binding("Tag");
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var theme = new ControlTheme(typeof(Control))
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{
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Setters = { new Setter(Control.TagProperty, binding) },
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};
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target.Theme = theme;
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var root = new TestRoot(target);
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root.UpdateLayout();
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Binding_When_Bound_Via_ControlTheme_TemplateBinding()
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{
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var target = new Control();
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var binding = new TemplateBinding(Control.TagProperty);
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var theme = new ControlTheme(typeof(Control))
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{
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Setters = { new Setter(Control.TagProperty, binding) },
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};
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target.Theme = theme;
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var root = new TestRoot(target);
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root.UpdateLayout();
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Binding_When_Bound_Via_ControlTheme_Style()
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{
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var target = new Control { Classes = { "foo" } };
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var binding = new Binding("Tag");
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var theme = new ControlTheme(typeof(Control))
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{
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Children =
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{
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new Style(x => x.Nesting().Class("foo"))
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{
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Setters = { new Setter(Control.TagProperty, binding) },
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},
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}
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};
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target.Theme = theme;
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var root = new TestRoot(target);
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root.UpdateLayout();
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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[Fact]
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public void GetBindingExpressionBase_Returns_Binding_When_Bound_Via_Style()
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{
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var target = new Control();
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var binding = new Binding("Tag");
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var style = new Style(x => x.OfType<Control>())
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{
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Setters = { new Setter(Control.TagProperty, binding) },
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};
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var root = new TestRoot();
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root.Styles.Add(style);
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root.Child = target;
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root.UpdateLayout();
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var expression = BindingOperations.GetBindingExpressionBase(target, Control.TagProperty);
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Assert.NotNull(expression);
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}
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}

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