<asp:ScriptManager ID="ScriptManager1" runat="server">     </asp:ScriptManager>     <h2>         使用VS控件updatePanel实现无刷新     </h2>     <p>          <asp:UpdatePanel ID="UpdatePanel1" RenderMode="Block" UpdateMode="Conditional" runat="server">         <ContentTemplate>             点击按钮从服务器获取当前时间<asp:TextBox ID="txtTime" runat="server"></asp:TextBox>             <asp:Button ID="btn1" runat="server" Text="Button" onclick="btn1_Click" />         </ContentTemplate>         <Triggers>         <%--<asp:PostBackTrigger ControlID="btn1" />--%>         <asp:AsyncPostBackTrigger ControlID="btn1"/>         </Triggers>         </asp:UpdatePanel>     </p>

       protected void btn1_Click(object sender, EventArgs e)         {             txtTime.Text = DateTime.Now.ToString();         }