WPF 与 PlacementTarget 和relativeSource 绑定
您能解释一下以下 WPF 代码吗：
DataContext="{Binding Path=PlacementTarget,RelativeSource={x:Static RelativeSource.Self}}">
我发现它非常令人困惑。什么是放置目标，什么是相对来源？
Can you explain the following WPF code:
DataContext="{Binding Path=PlacementTarget,RelativeSource={x:Static RelativeSource.Self}}">
I find it extremely confusing. What is placement target and what is relative source?
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这看起来像是用于弹出元素的 hack，例如 ContextMenus 和 Popup-windows。
这些元素的问题是，它们与窗口的可视化树断开连接。因此，
DataContext不可用。PlacementTarget是指向视觉树元素的链接。大多数情况下，您会发现类似
PlacementTarget.Tag的绑定路径，其中在源元素中Tag属性已设置为DataContext但在某些情况下，元素本身也是有意义的，例如在您的示例中。假设上面的代码用在
ToolTip或ContextMenu中，DataContext将被设置为“拥有”该元素的控件。请参阅 (Gishu +1) 的帖子了解机制的解释。
This looks like a hack that is used for popup-elements such as
ContextMenusandPopup-windows.The problem with these elements is, that they are disconnected from the visual tree of your window. Therefore the
DataContextis not available. ThePlacementTargetis a link to an element of the visual-tree.Mostly you will find a binding path like
PlacementTarget.Tagwhere in the source element theTagproperty has been set to theDataContextbut in some situations, the element itself is also meaningful, such as in your example.Assuming that the above code is used in a
ToolTipor aContextMenu, theDataContextwill be set to the control that "owns" the element.Look at the post from (Gishu +1) for an explanation of the mechanics.
每个
FrameworkElement都有一个DataContext，它是任意对象。数据绑定的默认源是DataContext。您可以使用RelativeSource.Self将绑定源更改为FrameworkElement本身，而不是其DataContext。因此，RelativeSource部分只是将您从FrameworkElement的DataContext移动到FrameworkElement本身。到达FrameworkElement后，您可以指定其任何属性的路径。如果FrameworkElement是一个Popup，它将有一个PlacementTarget属性，该属性是FrameworkElement>Popup 相对于定位。简而言之，例如，如果您有一个相对于
TextBox放置的Popup，则该表达式会设置Popup的DataContextcode> 到TextBox，结果Popup正文中的{Binding Text}将绑定到的文本>文本框。Every
FrameworkElementhas aDataContextthat is an arbitrary object. The default source for a data binding is thatDataContext. You can useRelativeSource.Selfto change the source for a binding to theFrameworkElementitself instead of itsDataContext. So theRelativeSourcepart just moves you "up one level" from theDataContextof theFrameworkElementto theFrameworkElementitself. Once you are at theFrameworkElementyou can specify a path to any of its properties. If theFrameworkElementis aPopup, it will have aPlacementTargetproperty that is the otherFrameworkElementthat thePopupis positioned relative to.In short, if you have a
Popupplaced relative to aTextBoxfor example, that expression sets theDataContextof thePopupto theTextBoxand as a result{Binding Text}somewhere in the body of thePopupwould bind to the text of theTextBox.这是将某个事物（UI 控件？需要查看更多代码片段）的 DataContext 绑定到它自己的 PlacementTarget 属性值。
RelativeSource 用于指示相对于绑定目标的源对象。路径属性指示源对象上的属性名称。
This is binding the DataContext of a thing (UI Control? need to see more of the code snippet ) to its own PlacementTarget property value.
RelativeSource is used to indicate the source object relative to the binding target. The path property indicates the name of the property on the source object.