vs.net控件updatePanel实现无刷新的方法

asp:ScriptManager ID="ScriptManager1" runat="server">
    /asp:ScriptManager>
    h2>
        使用VS控件updatePanel实现无刷新
    /h2>
    p>
        nbsp;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();
        }