WPF MVVM模式ListBox下ContextMenu绑定Command的方法以及将所选的Item的数据传回去

需求：ListBoxItem上右键，将数据传参。

疑问：ContextMenu不继承DataContext，导致直接用RelativeSource找根的方式也绑定不到。

解决方法：在ListBox.ContextMenu里写菜单，就可以直接绑定到ViewModel层的命令了，参数先用RelativeSource找到ContextMenu，再绑定PlacementTarget.SelectedItem。

<ListBox 
    x:Name="ResultBox" 
    Margin="0, 10, 0, 0" 
    Grid.Row="1"
    BorderThickness="0"
    ScrollViewer.VerticalScrollBarVisibility="Auto"
    PreviewMouseDoubleClick="ResultBox_PreviewMouseDoubleClick"
    ItemsSource="{Binding resultFiles, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <TextBlock Text="{Binding FileName}" FontSize="18" FontWeight="Bold"/>
                <TextBlock Text="{Binding FilePath}" Foreground="Gray"/>
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
    <ListBox.ContextMenu>
        <ContextMenu>
            <MenuItem x:Name="OpenFile" Header="打开文件"
                        Command="{Binding OpenFileCommand}"
                        CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ContextMenu}, Path=PlacementTarget.SelectedItem}"/>
            <MenuItem x:Name="OpenFolder" Header="打开文件所在文件夹" Click="OpenFolder_Click"/>
        </ContextMenu>
    </ListBox.ContextMenu>
</ListBox>