如何将MenuItem.Header绑定到Window / UserControl依赖项属性？ [英] How to bind MenuItem.Header to Window/UserControl dependency property?

问题描述

我想知道如何将MenuItem.Header绑定到父Window / UserControl依赖项属性？这是一个简单的示例：

I`m wondering how can I bind MenuItem.Header to the parent Window/UserControl dependency property? Here is a simple example:

Window1.xaml ：

<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300" x:Name="self">
    <Grid>
        <Grid.ContextMenu>
            <ContextMenu>
                <MenuItem Header="{Binding Path=MenuText, ElementName=self}" />
            </ContextMenu>
        </Grid.ContextMenu>
        <TextBlock Text="{Binding Path=MenuText, ElementName=self}"/>
    </Grid>
</Window>

Window1.xaml.cs ：

public partial class Window1 : Window {
    public static readonly DependencyProperty MenuTextProperty = DependencyProperty.Register(
        "MenuText", typeof (string), typeof (Window1), new PropertyMetadata("Item 1"));

    public Window1()
    {
        InitializeComponent();
    }

    public string MenuText {
        get { return (string)this.GetValue(MenuTextProperty); }
        set { this.SetValue(MenuTextProperty, value); }
    }
}

在我的情况下，文本块显示项目1 ，并且上下文菜单显示空白项目。我做错了什么？在我看来，我似乎对WPF数据绑定原则有严重的误解。

In my case, textblock displays "Item 1", and context menu displays empty item. What I`m doing wrong? It seems for me, that I faced serious misunderstaning of WPF databinding principles.

推荐答案

您应该在Visual的输出窗口中看到这一点。 Studio：

You should see this in the Output window of Visual Studio:

System.Windows.Data错误：4：
找不到引用
'ElementName进行绑定的源=自我'。
BindingExpression：Path = MenuText;
DataItem = null;目标元素是
‘MenuItem’（Name =’’）；目标属性
是标题（类型为对象）

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=self'. BindingExpression:Path=MenuText; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Header' (type 'Object')

这是因为ContextMenu与VisualTree断开了连接，您需要以不同的方式进行此绑定。

That is because the ContextMenu is disconnected from the VisualTree, you need to do this Binding differently.

一种方法是通过 ContextMenu.PlacementTarget （应该是网格） ，则可以使用其DataContext建立绑定，例如：

One way is via ContextMenu.PlacementTarget (which should be the Grid), you could use its DataContext to establish a binding, e.g.:

<MenuItem Header="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu}, Path=PlacementTarget.DataContext.MenuText}"/>

或在ContextMenu本身中设置DataContext：

or set up the DataContext in the ContextMenu itself:

<ContextMenu DataContext="{Binding RelativeSource={RelativeSource Self}, Path=PlacementTarget.DataContext}">
    <MenuItem Header="{Binding Path=MenuText}"/>
</ContextMenu>

如果这不是一个选项（因为网格的DataContext不能是Window / UserControl），可以尝试通过网格的 Tag 将引用传递给Window / UserControl。

If this is not an option (because the DataContext of the Grid cannot be the Window/UserControl) you can try to pass the reference to the Window/UserControl through the Tag of your Grid for example.

<Grid ...
      Tag="{x:Reference self}">
    <Grid.ContextMenu>
        <!-- The DataContext is now bound to PlacementTarget.Tag -->
        <ContextMenu DataContext="{Binding RelativeSource={RelativeSource Self}, Path=PlacementTarget.Tag}">
            <MenuItem Header="{Binding Path=MenuText}"/>
        </ContextMenu>
    ...

---

注意：由于这种行为，我倾向于在 App.xaml 中定义一个助手样式，以使所有ContextMenu从其父级伪继承 DataContext：

---

As a side-note: Because of this behavior i tend to define a helper-style in App.xaml to make all ContextMenus "pseudo-inherit" the DataContext from their parent:

    <!-- Context Menu Helper -->
    <Style TargetType="{x:Type ContextMenu}">
        <Setter Property="DataContext" Value="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}"/>
    </Style>

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