参考

在body中添加

 <asp:ScriptManager ID="sm" runat="server" AsyncPostBackTimeout="360" >

    </asp:ScriptManager>

 <asp:UpdatePanel ID="up" runat="server"><ContentTemplate>

                    <asp:Button ID="Save" runat="server" Text="Save" οnclick="Save_Click"/>   

                          </ContentTemplate></asp:UpdatePanel>

后台代码就是：

 if (no_Of_Like == "") ShowMsg(sender, "Please input No.of Likes!");

private void ShowMsg(object sender, string msg)

        {

            ///获取弹出对话框的按钮

            Button button = (Button)sender;

            ///注册对话框的脚本

            ScriptManager.RegisterClientScriptBlock(

            button,

            button.GetType(),

            button.UniqueID,

            "alert('" + msg + "');",

            true);

        }