WPF：将ContextMenu绑定到MVVM命令 [英] WPF: Binding a ContextMenu to an MVVM Command

问题描述

假设我有一个窗口，返回一个命令的属性（实际上，它是一个在ViewModel类中使用Command的UserControl，但让我们尽可能简单地重现问题）。

以下作品：

 < Window x：Class =Window1... x：Name =myWindow> 
< Menu> 
< MenuItem Command ={Binding MyCommand，ElementName = myWindow}Header =Test/> 
< / Menu> 
< / Window> 
  

但以下内容无效。

 < Window x：Class =Window1... x：Name =myWindow> 
< Grid> 
< Grid.ContextMenu> 
< ContextMenu> 
< MenuItem Command ={Binding MyCommand，ElementName = myWindow}Header =Test/> 
< / ContextMenu> 
< /Grid.ContextMenu> 
< / Grid> 
< / Window> 
  

我收到的错误消息是

System.Windows.Data错误：4：找不到引用ElementName = myWindow的绑定源。 BindingExpression：Path = MyCommand; DataItem = null; target元素是'MenuItem'（Name =''）;目标属性为'Command'（类型'ICommand'）

为什么？我该如何解决这个问题？使用 DataContext 不是一个选项，因为这个问题发生在视觉树下，DataContext已经包含正在显示的实际数据。我已经尝试使用 {RelativeSource FindAncestor，...} ，但是会产生类似的错误消息。

解决方案

请参阅

更新

很遗憾，引用的博客是没有更多的可用。我试图在另一个SO答案中解释这一进程。可以在这里找到。

Let's say I have a Window with a property returning a Command (in fact, it's a UserControl with a Command in a ViewModel class, but let's keep things as simple as possible to reproduce the problem).

The following works:

<Window x:Class="Window1" ... x:Name="myWindow">
    <Menu>
        <MenuItem Command="{Binding MyCommand, ElementName=myWindow}" Header="Test" />
    </Menu>
</Window>

But the following does not work.

<Window x:Class="Window1" ... x:Name="myWindow">
    <Grid>
        <Grid.ContextMenu>
            <ContextMenu>
                <MenuItem Command="{Binding MyCommand, ElementName=myWindow}" Header="Test" />
            </ContextMenu>            
        </Grid.ContextMenu>
    </Grid>
</Window>

The error message I get is

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=myWindow'. BindingExpression:Path=MyCommand; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand')

Why? And how do I fix this? Using the DataContext is not an option, since this problem occurs way down the visual tree where the DataContext already contains the actual data being displayed. I already tried using {RelativeSource FindAncestor, ...} instead, but that yields a similar error message.

解决方案

See this article from Justin Taylor for a workaround.

Update
Sadly, the referenced blog is no more available. I have tried to explain the proceeding in another SO-answer. It can be found here.

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