GridView的使用和嵌套DropDownList

在GridView中 经常要嵌套DropDownList dropDownList也需要设置默认选择值

                     < asp:TemplateField >
                         < HeaderTemplate > 实验班级 </ HeaderTemplate >
                         < ItemTemplate >
                             <% #DataBinder.Eval(Container.DataItem,"className")  %>
                         </ ItemTemplate >
                         < EditItemTemplate >
                             < asp:DropDownList  ID ="DpClass"  runat ="server"  DataSource ="<%#DB_class.ReturnAllClassInfo() %>"  DataTextField ="className"  DataValueField ="classID" ></ asp:DropDownList >
                         </ EditItemTemplate >
                     </ asp:TemplateField >

其中DB_Class.ReturnAllClassInfo返回一个DataSet 用于绑定

         if  ((e.Row.RowState  &  DataControlRowState.Edit)  !=   0 )
         {
            //设置编辑状态时文本框的大小
            TextBox tb = e.Row.Cells[4].Controls[0] as TextBox;
            tb.Width = new Unit(100);
            tb = e.Row.Cells[5].Controls[0] as TextBox;
            tb.Width = new Unit(100);
            //设置DropDownList选中项..
            DataRowView dr = e.Row.DataItem as DataRowView;//获取当前的数据行.
            DropDownList dpClass = e.Row.FindControl("DpClass") as DropDownList;
            dpClass.SelectedIndex = dpClass.Items.IndexOf(dpClass.Items.FindByText(dr["className"].ToString()));
            DropDownList dpLaboratory = e.Row.FindControl("DpLaboratory") as DropDownList;
            dpLaboratory.SelectedIndex = dpLaboratory.Items.IndexOf(dpLaboratory.Items.FindByText(dr["LaboratoryName"].ToString()));
        }

此代码用在RowDataBound中
DataRowView dr=e.Row.DataItem as DataRowView 获取当前的数据行
DropDownList.Item.IndexOf(DropDownList.Items.FindByText("string"))设置默认选项