ASP.NET/C#:DropDownList在服务器控件中没有触发的SelectedIndexChanged

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BindDropDownList();
        DropDownList1.AutoPostBack = true;
    }
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    // 在这里处理所选项的更改
}

<asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged" />
    </Triggers>
   <ContentTemplate>
        <!-- 在这里放置需要更新的控件 -->
    </ContentTemplate>
</asp:UpdatePanel>