DataGrid列头 checkBox 绑定方式

<DataGridTemplateColumn.HeaderTemplate>
   <DataTemplate>
       <CheckBox x:Name="chkSelectAll" HorizontalAlignment="Center" VerticalAlignment="Center"  Click="SelectedAll_Checked"  
             IsChecked="{Binding RelativeSource={RelativeSource AncestorType={x:Type DataGrid} },Path=DataContext.IsCheckedAll}">全选</CheckBox>
  </DataTemplate>
</DataGridTemplateColumn.HeaderTemplate>