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Rather than just use a standard `Binding`, make `TemplateBinding` a lightweight binding in the case where the binding is simply to a property on the templated parent.pull/1695/head
Steven Kirk
8 years ago
21 changed files with 285 additions and 108 deletions
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using System; |
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using System.Globalization; |
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using System.Reactive.Subjects; |
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using Avalonia.Data.Converters; |
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using Avalonia.Reactive; |
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namespace Avalonia.Data |
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{ |
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/// <summary>
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/// A XAML binding to a property on a control's templated parent.
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/// </summary>
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public class TemplateBinding : SingleSubscriberObservableBase<object>, |
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IBinding, |
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IDescription, |
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ISubject<object> |
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{ |
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private IStyledElement _target; |
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private Type _targetType; |
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/// <inheritdoc/>
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public InstancedBinding Initiate( |
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IAvaloniaObject target, |
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AvaloniaProperty targetProperty, |
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object anchor = null, |
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bool enableDataValidation = false) |
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{ |
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// Usually each `TemplateBinding` will only be instantiated once; in this case we can
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// use the `TemplateBinding` object itself as the instanced binding in order to save
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// allocating a new object. If the binding *is* instantiated more than once (which can
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// happen if it appears in a `Setter` for example, then just make a clone and instantiate
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// that.
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if (_target == null) |
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{ |
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_target = (IStyledElement)target; |
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_targetType = targetProperty?.PropertyType; |
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return new InstancedBinding( |
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this, |
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Mode == BindingMode.Default ? BindingMode.OneWay : Mode, |
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BindingPriority.TemplatedParent); |
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} |
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else |
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{ |
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var clone = new TemplateBinding |
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{ |
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Converter = Converter, |
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ConverterParameter = ConverterParameter, |
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Property = Property, |
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}; |
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return clone.Initiate(target, targetProperty, anchor, enableDataValidation); |
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} |
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} |
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/// <summary>
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/// Gets or sets the <see cref="IValueConverter"/> to use.
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/// </summary>
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public IValueConverter Converter { get; set; } |
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/// <summary>
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/// Gets or sets a parameter to pass to <see cref="Converter"/>.
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/// </summary>
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public object ConverterParameter { get; set; } |
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/// <summary>
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/// Gets or sets the binding mode.
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/// </summary>
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public BindingMode Mode { get; set; } |
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/// <summary>
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/// Gets or sets the name of the source property on the templated parent.
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/// </summary>
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public AvaloniaProperty Property { get; set; } |
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/// <inheritdoc/>
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public string Description => "TemplateBinding: " + Property; |
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void IObserver<object>.OnCompleted() => throw new NotImplementedException(); |
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void IObserver<object>.OnError(Exception error) => throw new NotImplementedException(); |
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void IObserver<object>.OnNext(object value) |
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{ |
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if (_target.TemplatedParent != null && Property != null) |
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{ |
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if (Converter != null) |
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{ |
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value = Converter.ConvertBack( |
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value, |
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Property.PropertyType, |
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ConverterParameter, |
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CultureInfo.CurrentCulture); |
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} |
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_target.TemplatedParent.SetValue(Property, value, BindingPriority.TemplatedParent); |
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} |
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} |
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protected override void Subscribed() |
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{ |
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TemplatedParentChanged(); |
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_target.PropertyChanged += TargetPropertyChanged; |
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} |
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protected override void Unsubscribed() |
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{ |
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if (_target.TemplatedParent != null) |
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{ |
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_target.TemplatedParent.PropertyChanged -= TemplatedParentPropertyChanged; |
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} |
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_target.PropertyChanged -= TargetPropertyChanged; |
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} |
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private void PublishValue() |
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{ |
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if (_target.TemplatedParent != null) |
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{ |
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var value = Property != null ? |
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_target.TemplatedParent.GetValue(Property) : |
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_target.TemplatedParent; |
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if (Converter != null) |
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{ |
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value = Converter.Convert(value, _targetType, ConverterParameter, CultureInfo.CurrentCulture); |
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} |
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PublishNext(value); |
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} |
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else |
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{ |
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PublishNext(AvaloniaProperty.UnsetValue); |
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} |
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} |
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private void TemplatedParentChanged() |
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{ |
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if (_target.TemplatedParent != null) |
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{ |
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_target.TemplatedParent.PropertyChanged += TemplatedParentPropertyChanged; |
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} |
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PublishValue(); |
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} |
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private void TargetPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e) |
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{ |
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if (e.Property == StyledElement.TemplatedParentProperty) |
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{ |
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var oldValue = (IAvaloniaObject)e.OldValue; |
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var newValue = (IAvaloniaObject)e.OldValue; |
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if (oldValue != null) |
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{ |
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oldValue.PropertyChanged -= TemplatedParentPropertyChanged; |
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} |
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TemplatedParentChanged(); |
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} |
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} |
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private void TemplatedParentPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e) |
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{ |
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if (e.Property == Property) |
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{ |
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PublishNext(_target.TemplatedParent.GetValue(Property)); |
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} |
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} |
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} |
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} |
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