C# Silverlight 5数据网格中具有祖先相对资源绑定的展开/折叠按钮

我发现了几篇关于在SL3和SL4中实现扩展/折叠的文章，它们实际上是缺少的“祖先相对资源绑定”的变通方法。所以现在SL5已经发布了，我想知道SL5是如何做到这一点的

以下是SL4的答案：

使用SL5，操作起来很简单：

<sdk:DataGrid ItemsSource="{Binding Items}" 
   AutoGenerateColumns="False" 
   RowDetailsVisibilityMode="Collapsed">
   <sdk:DataGrid.Resources>
     <SL5:VisibilityToBoolConverter x:Key="converter"/>
   </sdk:DataGrid.Resources>
   <sdk:DataGrid.Columns>
      <sdk:DataGridTemplateColumn>
         <sdk:DataGridTemplateColumn.CellTemplate>
            <DataTemplate>
              <ToggleButton Content="Expand" 
                  IsChecked="{Binding Path=DetailsVisibility, 
                  Mode=TwoWay, 
                  RelativeSource={RelativeSource AncestorType=sdk:DataGridRow},
                  Converter={StaticResource converter}}"/>
            </DataTemplate>
          </sdk:DataGridTemplateColumn.CellTemplate>
       </sdk:DataGridTemplateColumn>
   </sdk:DataGrid.Columns>
</sdk:DataGrid>

public class VisibilityToBoolConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        CultureInfo culture)
    {
        Visibility visibility = (Visibility)value;
        return (visibility == Visibility.Visible);
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        CultureInfo culture)
    {
        bool visibility = (bool)value;
        return visibility ? Visibility.Visible : Visibility.Collapsed;
    }
}