wpf 获取datagrid中模板中控件

 //获取name为datagrid中第三列第一行模板的控件
            FrameworkElement item = dataGrid.Columns[3].GetCellContent(dataGrid.Items[0]);
            DataGridTemplateColumn temp = dataGrid.Columns[3] as DataGridTemplateColumn;
            //img是模板的name
            object c= temp.CellTemplate.FindName("img", item);
            if (c is System.Windows.Controls.Image)
            {
                Image b = c as Image;
                //重新赋值图片
                Uri cs = new Uri(@"image/r.jpg", UriKind.RelativeOrAbsolute);
                ImageSource bs = new BitmapImage(cs);
                b.Source = bs;
            }