如何從UserControl的ContextMenu引用UserControl樣式的元素？

Question

給定一個包含包含上下文菜單和控件模板的MVVM模式的用戶控件，如何從上下文菜單中引用樣式內的元素？ 除MenuItem CommandParameter之外，以下代碼似乎正常運行。 “ Template.MyViewBox.Child”的綁定路徑顯然不起作用，但演示了我要完成的目的。

<UserControl x:Class="MyViewer.Views.IconView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:MyViewer.ViewModels">

<UserControl.Resources>
    <vm:ViewModelLocator x:Key="Locator" />
</UserControl.Resources>

<UserControl.DataContext>
    <Binding Source="{StaticResource Locator}" Path="Main" />
</UserControl.DataContext>

<UserControl.ContextMenu>
    <ContextMenu x:Name="CtContextMenu"
                  DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource Self}}">
        <MenuItem Header="Print Current View"
                  Command="{Binding Path=DataContext.PrintCurrentViewCmd}"
                  CommandParameter="{Binding Path=Template.MyViewBox.Child}"/>
    </ContextMenu>
</UserControl.ContextMenu>

<UserControl.Style>
    <Style TargetType="{x:Type UserControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type UserControl}" >
                    <Viewbox x:Name="MyViewBox">
                        <ContentControl Name="MyContentControl" Content="{TemplateBinding Content}" />
                    </Viewbox>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</UserControl.Style>

Answer 1

上下文菜單是一個彈出窗口，它在其自己的可視樹中呈現，而不是作為其父級的子級呈現。 要實現您需要做的事情，您可以執行以下操作

<UserControl x:Class="MyViewer.Views.IconView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:vm="clr-namespace:MyViewer.ViewModels" 
         Tag="{Binding Path=Child, RelativeSource={RelativeSource AncestorType={x:Type ViewBox}}}">

<UserControl.Resources>
    <vm:ViewModelLocator x:Key="Locator" />
</UserControl.Resources>

<UserControl.DataContext>
    <Binding Source="{StaticResource Locator}" Path="Main" />
</UserControl.DataContext>

<UserControl.ContextMenu>
    <ContextMenu x:Name="CtContextMenu"
                  DataContext="{Binding Path=PlacementTarget, RelativeSource={RelativeSource Self}}">
        <MenuItem Header="Print Current View"
                  Command="{Binding Path=DataContext.PrintCurrentViewCmd}"
                  CommandParameter="{Binding Path=PlacementTarget.Tag,Element=CtContextMenu}"/>
    </ContextMenu>
</UserControl.ContextMenu>

<UserControl.Style>
    <Style TargetType="{x:Type UserControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type UserControl}" >
                    <Viewbox x:Name="MyViewBox">
                        <ContentControl Name="MyContentControl" Content="{TemplateBinding Content}" />
                    </Viewbox>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</UserControl.Style>