<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
//ASP.NET中使用UpdatePanel实现局部异步刷新
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:DropDownList runat="server" ID="SelectProductType" AutoPostBack="True" OnSelectedIndexChanged="SelectProductTypeChange" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="SelectProductType" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
//后台下拉框选择改变触发事件
protected void SelectProductTypeChange(object sender, EventArgs e)
{
//
}