在DataGrid的外面得到Footer中的控件

   string hisid=txtHisID.Text.Trim();
    if(hisid=="-1")
    {
     DataGridItem footer = (DataGridItem)DataGrid1.Controls[0].Controls[DataGrid1.Controls[0].Controls.Count-1];
     DropDownList cboProxyObj=((DropDownList) footer.FindControl("cboProxy"));
     cboProxyObj.DataSource=HospitalBase.GetProxyByhisid(hisid);
     cboProxyObj.DataBind();
    }