MVVM datatemplate 下button.contextmenu的command 失效解决方案

 <Button CommandParameter="{Binding}"
 Tag="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type pagesView:OutputPage}}}"
 Command = "{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type pagesView:OutputPage}}, Path=DataContext.EditOutputCommand}">
 <Button.ContextMenu>
 <ContextMenu>
 <MenuItem Header="削除"
 CommandParameter="{Binding}"
 Command="{Binding Path=PlacementTarget.Tag.DataContext.DeleteCurrentLineCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ContextMenu}}"/>
 </ContextMenu>
 </Button.ContextMenu>
 </Button>

button.contextmenu的command 失效；

参考地址：http://stackoverflow.com/questions/9994241/mvvm-binding-command-to-contextmenu-item