如何获得DataGrid中某行某列的对象

假如某行是

            Xm_struct x = this.Brow.SelectedItem as Xm_struct;
则下面分别是第5和第七列的对象 

           TextBlock Ddjs = this.Brow.Columns[4].GetCellContent(x) as TextBlock;
            TextBlock Dj = this.Brow.Columns[6].GetCellContent(x) as TextBlock;