e.NewValues 在 Asp.Net DetailsView ItemUpdate 中返回 Null

我有一个详细信息视图来显示用户详细信息并在必要时进行更新。我正在使用 e.NewValues 来获取要更新的编辑状态值。但它会引发空异常。代码如下。

    <asp:DetailsView ID="MyDetailsView" CssClass="gv" runat="server" Width="100%" CellPadding="15"
    ForeColor="#333333" AutoGenerateEditButton="True" OnModeChanging="MyDetailsView_ModeChanging"
    AutoGenerateRows="False" OnItemUpdating="MyDetailsView_ItemUpdating">
    <FieldHeaderStyle CssClass="gvheader" Width="100px" />
    <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <CommandRowStyle BackColor="#E2DED6" Font-Bold="True" />
    <RowStyle BackColor="White" ForeColor="#333333" BorderColor="#666666" />
    <FieldHeaderStyle BackColor="#6F97BA" Font-Bold="True" ForeColor="White" />
    <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
    <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <EditRowStyle BackColor="white" />
    <Fields>
        <asp:BoundField HeaderText="Address" DataField="Address" SortExpression="Address">
            <ControlStyle Height="25px" Width="450px" />
        </asp:BoundField>
        <asp:BoundField HeaderText="Postcode" DataField="Postcode" SortExpression="Postcode">
            <ControlStyle Height="25px" Width="450px" />
        </asp:BoundField>
        <asp:BoundField HeaderText="Country" DataField="Countries" SortExpression="Countries">
            <ControlStyle Height="25px" Width="450px" />
        </asp:BoundField>
    </Fields>
    </asp:DetailsView>

代码隐藏

    protected void MyDetailsView_ItemUpdating(object sender, DetailsViewUpdateEventArgs e)
{
    string address = e.NewValues["Address"].ToString();
    string postcode = e.NewValues["Postcode"].ToString();
    string country = e.NewValues["Countries"].ToString();
    Client c = new Client();
    c.UpdateMyDetails((string)Session["Code"], address, postcode, country); 
    MyDetailsView.ChangeMode(DetailsViewMode.ReadOnly); 
    MyDetailsView.DataBind();
}

有人可以帮忙吗？