gridview 的dropdownlist绑定数据有关问题

gridview 的dropdownlist绑定数据问题
我在gridview里放了个下拉菜单 现在从数据库里读取一行数据绑定在gridview里 将其中的一列数据绑定在dropdownlist里 参照网上的说法 谢啦个rowdatabound事件 不知道哪里出错了 下拉菜单并没有绑定上数据

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)

        {

            if (e.Row.RowType == DataControlRowType.DataRow)

            {                

                    string sql = "select * from EP_TblMailbox where SendToDepartment = '维修部'";

                    SqlDataReader sdr = dataOperate.getRow(sql);

                    sdr.Read();

                    if (sdr["IsVisted"].ToString() =="true")

                    {

                        DropDownList ddl = (DropDownList)e.Row.Cells[0].FindControl("DropDownList2");

                        ddl.SelectedValue = "是";

                    }

                    if (sdr["IsVisted"].ToString() == "false")

                    {

                        DropDownList ddl = (DropDownList)e.Row.Cells[0].FindControl("DropDownList2");

                        ddl.SelectedValue="否";

                    }                

            }            

        }

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 

            onrowdatabound="GridView1_RowDataBound">

            <Columns>

                <asp:BoundField DataField="ID" HeaderText="编号" />

                <asp:BoundField DataField="SenderName" HeaderText="发送人" />

                <asp:BoundField DataField="SendDepartment" HeaderText="发送部门" />