如何實現vs.net控件updatePanel無刷新

    頁面部分
    代碼如下:
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <h2>
    使用VS控件updatePanel實現無刷新
    </h2>
    <p>
    <asp:UpdatePanel ID="UpdatePanel1" RenderMode="Block" UpdateMode="Conditional" runat="server">
    <ContentTemplate>
    點擊按鈕從服務器獲取當前時間<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>
    后臺代碼
    代碼如下:
    protected void btn1_Click(object sender, EventArgs e)
    {
    txtTime.Text = DateTime.Now.ToString();
    }