AJAX 中Sys.WebForms.PageRequestManager的事件激发顺序 《转》

<asp:ScriptManager ID="ScriptManager1" runat="server" />
    <asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="0" DynamicLayout="false">
        <ProgressTemplate>
            <span style="color: Red" mce_style="color: Red">Loading...</span>
        </ProgressTemplate>
    </asp:UpdateProgress>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <%=DateTime.Now %><br />
            <asp:Label ID="Label1" runat="server" Text=""></asp:Label><br />
            <asp:Button ID="btnPrecedence" runat="server" Text="优先" OnClick="btnPrecedence_Click" />
            <asp:Button ID="Button2" runat="server" Text="普通" OnClick="btnPrecedence_Click" />
        </ContentTemplate>
    </asp:UpdatePanel>
    <div id="Message" style="color: Red" mce_style="color: Red">
    </div>

    <mce:script type="text/javascript" language="javascript"><!--
        var lastPostBackButtonId=null;          //上一次事件 控件ID
        var btnPrecedenceId = "<%=this.btnPrecedence.ClientID %>"   //优先级高的控件ID
        
        Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(
            function(sender,e)
            {
                //定义一个全局PageRequestManager实例赋值给变量 prm
                var prm = Sys.WebForms.PageRequestManager.getInstance();
                //是否已有异步刷新
                if(prm.get_isInAsyncPostBack())
                {
                    if(lastPostBackButtonId==btnPrecedenceId)       //上次跟本次都是点击优先按钮
                    {
                        e.set_cancel(true);//取消异步更新
                        if(e.get_postBackElement().id==btnPrecedenceId)
                        {
                            showMessage("不可重复发起优先的刷新1。");
                        }else
                        {
                            showMessage("请等待优先的刷新结束2。");
                        }
                        return;
                    }
                    else if(e.get_postBackElement().id==btnPrecedenceId) //本次点击是优先按钮,但上次却不是优先按钮
                    {
                        showMessage("发起优先的刷新，普通的刷新将被取消3。");
                    }
                    else //本次点击不是优先按钮，上次点击也不是优先按钮
                    {
                        showMessage("重新发起普通刷新，前一次将被取消4。");
                    }
                }
                lastPostBackButtonId = e.get_postBackElement().id;
            }
        );
    
// --></mce:script>

    <mce:script type="text/javascript" language="javascript"><!--
            var timeoutSeed = null;
            function showMessage(message,timeout)
            {
                $get("Message").innerHTML = message;
                //连续发送请求，把前一个清楚掉
                if(timeoutSeed)
                {
                    window.clearTimeout(timeoutSeed);
                }
                timeoutSeed = window.setTimeout(function(){$get("message").innerHTML="";
                },timeout||2500)
            }
            
    
// --></mce:script>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <%=DateTime.Now %><br />
            <asp:Button ID="Button1" runat="server" Text="Button1" OnClick="Button_Click" />
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="Button2" />
        </Triggers>
    </asp:UpdatePanel>
    <asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="0" AssociatedUpdatePanelID="UpdatePanel1">
        <ProgressTemplate>
            <span style="color: Red" mce_style="color: Red">Loading...</span>
        </ProgressTemplate>
    </asp:UpdateProgress>
    <hr />
    <asp:Button ID="Button2" runat="server" Text="Button2" OnClick="Button_Click" />

    <mce:script type="text/javascript" language="javascript"><!--
        Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(
            function(sender,e)
            {
                if(e.get_postBackElement().id != "<%=this.Button2.ClientID %>")
                {
                    return;
                }
                
                var updateProgress = $get("<%=this.UpdateProgress1.ClientID %>");
                var dynamicLayout = <%=this.UpdateProgress1.DynamicLayout.ToString().ToLower() %>;
                if(dynamicLayout)
                {
                    updateProgress.style.display = "block";
                }else
                {
                    updateProgress.style.visibility = "visible";
                }
            }
        )
    
// --></mce:script>

 protected void Page_Load(object sender, EventArgs e)
    {
        ScriptManager.GetCurrent(Page).AsyncPostBackTimeout = 3;
    }
    protected void btnError_Click(object sender, EventArgs e)
    {
        int two = 2;
        int i = 3 / (two - 2);
    }
    protected void btnTimeout_Click(object sender, EventArgs e)
    {
        Thread.Sleep(5000);
    }
    protected void btnDataItem_Click(object sender, EventArgs e)
    {
        ScriptManager.GetCurrent(this).RegisterDataItem(UpdatePanel1, DateTime.Now.ToString());
    }