How do I set CommandParameter in XAML?

问题:

I have the following XAML:

   <dxg:GridControl Name="theGrid" DataSource="{Binding Path=Groupings}">
       <dxg:GridControl.ContextMenu>
           <ContextMenu>
               <MenuItem x:Name="gridprint" Command="{Binding Path=GridPrintCommand}"/>
           </ContextMenu>
       </dxg:GridControl.ContextMenu>
   </dxg:GridControl>

When GridPrintCommand executes, its parameter to the GridPrintCommand.Execute(param) method is null. I want to set the parameter to the grid control. I can do that in the code-behind like this:

gridprint.CommandParameter = theGrid;

This works fine. But I'm trying to set the same thing (CommandParameter) in the XAML, and I just can't get it right! Everything I put results in a BindingExpressionError or a null parameter. What am I missing?

回答1:

Try using this:

<MenuItem x:Name="gridprint"
    CommandParameter="{Binding PlacementTarget, RelativeSource=
         {RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}}" />

ContextMenus are not part of the WPF's normal VisualTree, so you have to bind using the PlacementTarget to get the object the ContextMenu is attached to

回答2:

I believe it should be this

<dxg:GridControl Name="theGrid" DataSource="{Binding Path=Groupings}">
  <dxg:GridControl.ContextMenu>
    <ContextMenu>
      <MenuItem x:Name="gridprint"
        Command="{Binding Path=GridPrintCommand}"
        CommandParameter="{Binding ElementName=theGrid}"
      />
    </ContextMenu>
  </dxg:GridControl.ContextMenu>