asp.net - 下拉菜单在 datagridview asp.net 中不起作用

Question

我想在 datagridview 中有下拉列表我收到以下错误 Object reference not set to an instance of an object 但我不明白为什么会收到此错误。

这是我的前端

  <asp:TemplateField HeaderText="Proveedor" >
                <ItemTemplate>                       
                    <asp:Label DataField="nombre_proveedor"  ID="lblSupplier" CssClass="gridTextbox" Text='<%# Eval("proveedor_id") %>' runat="server" />
                </ItemTemplate>
                <EditItemTemplate>   
            <asp:DropDownList  ID="drGridSupplier" Runat="server"  AutoPostBack="false"  OnSelectedIndexChanged="DropDown_SelectedIndexChanged" />
                </EditItemTemplate>
                <FooterTemplate>
                    <asp:TextBox  CssClass="gridTextbox" ID="txtSupplierFooter" runat="server" />
                </FooterTemplate>
            </asp:TemplateField>

这是我的后端。

protected void gvPurchases_RowDataBound(object sender, GridViewRowEventArgs e)
    {

        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            using (MySqlConnection conn = new MySql.Data.MySqlClient.MySqlConnection(connString))
            {
                conn.Open();
                DropDownList drGridSupplier = (e.Row.FindControl("drGridSupplier") as DropDownList);
                using (MySqlCommand cmdd = new MySql.Data.MySqlClient.MySqlCommand("select proveedor_id,nombre from erp_proveedores", conn))
                {
                    using (MySqlDataAdapter sdaa = new MySqlDataAdapter(cmdd))
                    {
                        DataTable dt = new DataTable();
                        sdaa.Fill(dt);
                        drGridSupplier.DataSource = dt;

                        drGridSupplier.DataTextField = "nombre";
                        drGridSupplier.DataValueField = "proveedor_id";
                        drGridSupplier.DataBind();
                        drGridSupplier.Items.Insert(0, new ListItem("--Select Qualification--", "0"));
                        conn.Close();
                    }
                }

            }

        }

    }

标签： asp.netdatagrid