winform 中显示异步下载的图片

private void dataGridView1_RowsAdded(object sender, DataGridViewRowsAddedEventArgs e){  ////利用 WebClient 来下载图片  using (WebClient wc = new WebClient())  {    ////WebClient 下载完毕的响应事件绑定    wc.DownloadDataCompleted += new DownloadDataCompletedEventHandler(wc_DownloadDataCompleted);    ////开始异步下载，图片URL路径请根据实际情况自己去指定    ////同时将DataGridView当前行的行号传递过去，用于指定图片显示的CELL    wc.DownloadDataAsync(new Uri(this.dataGridView1.Rows[e.RowIndex].Cells[1].Value.ToString()),      e.RowIndex);  }}void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e){  ////如果下载过程未发生错误，并且未被中途取消  if (e.Error == null && !e.Cancelled)  {    ////将图片显示于对应的指定单元格， e.UserState 就是传入的 e.RowIndex    ////e.Result 就是下载结果    this.dataGridView1.Rows[(int)e.UserState].Cells["src"].Value = e.Result;    // this.dataGridView1.Rows[(int)e.UserState].Cells["test"].Value = GetImage("1");  }}