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RelativeSource实现标记扩展，以描述绑定源相对于绑定目标的位置。
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// Summary: // Describes the location of the binding source relative to the position of // the binding target. public enum RelativeSourceMode { // Summary: // Allows you to bind the previous data item (not that control that contains // the data item) in the list of data items being displayed. PreviousData = 0, // // Summary: // Refers to the element to which the template (in which the data-bound element // exists) is applied. This is similar to setting a System.Windows.TemplateBindingExtension // and is only applicable if the System.Windows.Data.Binding is within a template. TemplatedParent = 1, // // Summary: // Refers to the element on which you are setting the binding and allows you // to bind one property of that element to another property on the same element. Self = 2, // // Summary: // Refers to the ancestor in the parent chain of the data-bound element. You // can use this to bind to an ancestor of a specific type or its subclasses. // This is the mode you use if you want to specify System.Windows.Data.RelativeSource.AncestorType // and/or System.Windows.Data.RelativeSource.AncestorLevel. FindAncestor = 3, }
Xaml 示例
RelativeSource内部实现
using System;using System.ComponentModel;using System.Windows.Markup;namespace System.Windows.Data{ public class RelativeSource : MarkupExtension, ISupportInitialize { public RelativeSource(); public RelativeSource(RelativeSourceMode mode); public RelativeSource(RelativeSourceMode mode, Type ancestorType, int ancestorLevel); public Type AncestorType { get; set; } public RelativeSourceMode Mode { get; set; } public static RelativeSource PreviousData { get; } public static RelativeSource Self { get; } public static RelativeSource TemplatedParent { get; } public override object ProvideValue(IServiceProvider serviceProvider); ... }} using System;using System.ComponentModel;using System.Windows.Markup; namespace System.Windows.Data{ /// Implements a markup extension that describes the location of the binding source relative to the position of the binding target. [MarkupExtensionReturnType(typeof(RelativeSource))] public class RelativeSource : MarkupExtension, ISupportInitialize { private RelativeSourceMode _mode; private Type _ancestorType; private int _ancestorLevel = -1; private static RelativeSource s_previousData; private static RelativeSource s_templatedParent; private static RelativeSource s_self; /// Gets a static value that is used to return a /// A static public static RelativeSource PreviousData { get { if (RelativeSource.s_previousData == null) { RelativeSource.s_previousData = new RelativeSource(RelativeSourceMode.PreviousData); } return RelativeSource.s_previousData; } } /// Gets a static value that is used to return a /// A static public static RelativeSource TemplatedParent { get { if (RelativeSource.s_templatedParent == null) { RelativeSource.s_templatedParent = new RelativeSource(RelativeSourceMode.TemplatedParent); } return RelativeSource.s_templatedParent; } } /// Gets a static value that is used to return a /// A static public static RelativeSource Self { get { if (RelativeSource.s_self == null) { RelativeSource.s_self = new RelativeSource(RelativeSourceMode.Self); } return RelativeSource.s_self; } } /// Gets or sets a /// One of the /// This property is immutable after initialization. Instead of changing the [ConstructorArgument("mode")] public RelativeSourceMode Mode {get { return this._mode; } set { if (this.IsUninitialized) { this.InitializeMode(value); return; } if (value != this._mode) { throw new InvalidOperationException(SR.Get("RelativeSourceModeIsImmutable")); } } } /// Gets or sets the type of ancestor to look for. /// The type of ancestor. The default value is null. /// The public Type AncestorType {get { return this._ancestorType; } set { if (this.IsUninitialized) { this.AncestorLevel = 1; } if (this._mode != RelativeSourceMode.FindAncestor) { if (value != null) { throw new InvalidOperationException(SR.Get("RelativeSourceNotInFindAncestorMode")); } } else { this._ancestorType = value; } } } /// Gets or sets the level of ancestor to look for, in /// The ancestor level. Use 1 to indicate the one nearest to the binding target element. public int AncestorLevel {get { return this._ancestorLevel; } set { if (this._mode != RelativeSourceMode.FindAncestor) { if (value != 0) { throw new InvalidOperationException(SR.Get("RelativeSourceNotInFindAncestorMode")); } } else { if (value < 1) { throw new ArgumentOutOfRangeException(SR.Get("RelativeSourceInvalidAncestorLevel")); } this._ancestorLevel = value; } } } private bool IsUninitialized { get { return this._ancestorLevel == -1; } } /// Initializes a new instance of the public RelativeSource() { this._mode = RelativeSourceMode.FindAncestor; } /// Initializes a new instance of the /// One of the Initializes a new instance of the /// One of the This member supports the Windows Presentation Foundation (WPF) infrastructure and is not intended to be used directly from your code. void ISupportInitialize.BeginInit() { } ///This member supports the Windows Presentation Foundation (WPF) infrastructure and is not intended to be used directly from your code. void ISupportInitialize.EndInit() { if (this.IsUninitialized) { throw new InvalidOperationException(SR.Get("RelativeSourceNeedsMode")); } if (this._mode == RelativeSourceMode.FindAncestor && this.AncestorType == null) { throw new InvalidOperationException(SR.Get("RelativeSourceNeedsAncestorType")); } } /// Indicates whether the /// true if the property value has changed from its default; otherwise, false. public bool ShouldSerializeAncestorType() { return this._mode == RelativeSourceMode.FindAncestor; } /// Indicates whether the /// true if the property value has changed from its default; otherwise, false. public bool ShouldSerializeAncestorLevel() { return this._mode == RelativeSourceMode.FindAncestor; } /// Returns an object that should be set as the value on the target object's property for this markup extension. For /// Another /// An object that can provide services for the markup extension. In this implementation, this parameter can be null. public override object ProvideValue(IServiceProvider serviceProvider) { if (this._mode == RelativeSourceMode.PreviousData) { return RelativeSource.PreviousData; } if (this._mode == RelativeSourceMode.Self) { return RelativeSource.Self; } if (this._mode == RelativeSourceMode.TemplatedParent) { return RelativeSource.TemplatedParent; } return this; } private void InitializeMode(RelativeSourceMode mode) { if (mode == RelativeSourceMode.FindAncestor) { this._ancestorLevel = 1; this._mode = mode; return; } if (mode == RelativeSourceMode.PreviousData || mode == RelativeSourceMode.Self || mode == RelativeSourceMode.TemplatedParent) { this._ancestorLevel = 0; this._mode = mode; return; } throw new ArgumentException(SR.Get("RelativeSourceModeInvalid"), "mode"); } }}
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