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