ASP.NET AJAX UpdatePanel 控件实现剖析

使用ASP.NET AJAX框架我们可以搭建快速响应、具有丰富的用户体验的AJAX Web应用程序，而该框架的UpdatePanel控件则提供了一种非常简单的方式来实现Web页面的局部更新，我们不需要在每次回发的时候都加载整个页面。

 

那这个控件是如何实现这种局部刷新的哪，透过其实现机制我们可以更清楚其优缺点，便于我们确定其使用场合。本文将重点阐述ASP.NET AJAX控件UpdatePanel的实现机制。

 

1． ASP.NET AJAX 简介 ASP.NET AJAX是微软在ASP.NET 2.0之上对AJAX技术的一个封装，为Web应用程序提供完整的AJAX解决方案。ASP.NET AJAX有两种编程模型：部分更新和远程服务。

 

部分更新使得用户可以用传统的ASP.NET 2.0应用程序的方式来搭建AJAX应用，具体就是使用UpdatePanel控件来实现无闪烁页面更新。而远程服务则是直接通过前端JavaScript来调用的服务器端服务，前段获取数据后，进行页面更新，这就要求服务器端代码必须分解为特定于应用程序的服务，这是与传统的ASP.NET应用程序完全不同的体系结构。

 

部分更新着重于对现有应用程序进行渐进式增强，帮助用户逐渐转换到纯粹的AJAX应用。本文主要对部分更新编程模型中核心控件UpdatePanel的实现进行剖析，讲述其背后的故事。

 

ASP.NET AJAX框架分为客户端以及服务器端两个部分，基于客户端的 Microsoft AJAX Library包含了对浏览器兼容性、网络访问以及客户端控件组件等支持， 而服务器端则包括了服务器控件，Web 服务等等。

 

见下图：

 

 

Microsoft Ajax Library就是ASP.NET AJAX的客户端脚本库，其中MicrosoftAjax.js包含了ASP.NET AJAX的核心内容，包括跨浏览器的支持、基于面向对象对JavaScript的扩展以及网络访问等等。MicrosoftAjaxWebForm.js文件则是完全服务于ASP.NET AJAX页面局部更新这样一个功能的，在该文件中定义了一个客户端对象PageRequestManager，该对象将会负责客户端异步回送的全过程。

 

2． ScriptManager 和 UpdatePanel ScriptManager和UpdatePanel是ASP.NET AJAX服务器端中最重要的两个控件，ScriptManager控件用来管理ASP.NET页面中的客户端脚本，生成及注册所需要的客户端脚本，通过UpdatePanel控件可以更新页面的指定部分而无需加载整个页面。

 

看个例子：

<form id="form1" runat="server">

   <asp:ScriptManager ID="ScriptManager1" runat="server">

   </asp:ScriptManager>

   <div>

      <asp:UpdatePanel ID="UpdatePanel1" runat="server">

           <ContentTemplate>

               <%= DateTime.Now %>

                <br />

               <asp:Button ID="Button1" runat="server" Text="Button" />

           </ContentTemplate>

       </asp:UpdatePanel>

   </div>

</form>

 

构建如上代码所示的页面，在Runtime点击UpdatePanel中的Button控件，则不会引起整个页面刷新，只是用来显示当前时间的Label得到更新。

这是如何实现的哪？

 

3． ASP.NET AJAX部分呈现剖析

 

3.1 先从客户端讲起

 

看一下上面的示例代码在客户端的HTML代码， 这里只列出核心部分，其他全部隐去。

<script type="text/javascript">

//<![CDATA[

Sys.WebForms.PageRequestManager._initialize('ScriptManager1', document.getElementById('form1'));

Sys.WebForms.PageRequestManager.getInstance()._updateControls(['tUpdatePanel1'], [], [], 90);

//]]>

</script>



<div id="UpdatePanel1">    

     7/25/2008 4:54:36 PM

     <br />

     <input type="submit" name="Button1" value="Button" id="Button1" />            

</div>

 

看一下上面的两句JavaScript代码，第一句代码中的_initialize 方法是客户端PageRequestManager对象上的静态方法，它会创建一个 PageRequestManager 类的全局实例，并将其初始化。在这个初始化函数中，ageRequestManager对象注册了当前表单对象的submit事件，以及window对象的load和unload事件。

 

而第二句代码则是通过PageRequestManager的getInstance方法来检索其唯一实例， 得到该实例后调用_updateControls方法来注册UpdatePanel以及其Trigger控件。

 

我们可以从MicrosoftAjaxWebForm.js文件中得到_updateControls方法的声明：

function Sys$WebForms$PageRequestManager$_updateControls(updatePanelIDs, asyncPostBackControlIDs, postBackControlIDs, asyncPostBackTimeout) {} 

由其中第一个参数代表了当前页面上所有的UpdatePanel控件的ID集合，如果该UpdatePanel的ChildrenAsTrigger为True的话，应在ID前添加字符't'，否则添加字符'f'；而第二个参数是所有引发异步回送的控件ID；第三个参数是所有引发同步回送的控件ID；第四个参数设定了异步回送的Timeout时间，单位为秒。于PageRequestManager对象注册了当前表单的submit时间，所以每当页面有提交动作的时候，PageRequestManager对象就会介入，看一下PageRequestManager对象页面提交处理函数_onFormSubmit(evt)。

 

如果需要执行一次异步回送的话，会中止原有的普通浏览器会回发，代之使用XMLHttpRequest进行AJAX回发。在封装这个请求的时候，当前页面的所有字段以及视图状态都会被打包在请求中，另外还设置了这次Request的HTTP头：request.get_headers()['X-MicrosoftAjax'] = 'Delta=true'；

 

在服务器端将会根据这个HTTP头标记来判定是否为一次AJAX异步回发。

 

_onFormSubmit(evt)函数代码：

function Sys$WebForms$PageRequestManager$_onFormSubmit(evt) {

        var continueSubmit = true;

        var isCrossPost = this._isCrossPost;

        this._isCrossPost = false;

        if (this._onsubmit) {

            continueSubmit = this._onsubmit();

        }

        if (continueSubmit) {

            for (var i = 0; i < this._onSubmitStatements.length; i++) {

                if (!this._onSubmitStatements[i]()) {

                    continueSubmit = false;

                    break;

                }

            }

        }

        if (!continueSubmit) {

            if (evt) {

                evt.preventDefault();

            }

            return;

        }

        var form = this._form;

        if (isCrossPost) {

            return;

        }

        if (this._activeDefaultButton && !this._activeDefaultButtonClicked) {

            this._onFormElementActive(this._activeDefaultButton, 0, 0);

        }

        if (!this._postBackSettings.async) {

            return;

        }

        var formBody = new Sys.StringBuilder();

        formBody.append(encodeURIComponent(this._scriptManagerID) + '=' + encodeURIComponent(this._postBackSettings.panelID) + '&');

        var count = form.elements.length;

        for (var i = 0; i < count; i++) {

            var element = form.elements[i];

            var name = element.name;

            if (typeof(name) === "undefined" || (name === null) || (name.length === 0)) {

                continue;

            }

            var tagName = element.tagName;

            if (tagName === 'INPUT') {

                var type = element.type;

                if ((type === 'text') ||

                    (type === 'password') ||

                    (type === 'hidden') ||

                    (((type === 'checkbox') || (type === 'radio')) && element.checked)) {

                    formBody.append(encodeURIComponent(name));

                    formBody.append('=');

                    formBody.append(encodeURIComponent(element.value));

                    formBody.append('&');

                }

            }

            else if (tagName === 'SELECT') {

                var optionCount = element.options.length;

                for (var j = 0; j < optionCount; j++) {

                    var option = element.options[j];

                    if (option.selected) {

                        formBody.append(encodeURIComponent(name));

                        formBody.append('=');

                        formBody.append(encodeURIComponent(option.value));

                        formBody.append('&');

                    }

                }

            }

            else if (tagName === 'TEXTAREA') {

                formBody.append(encodeURIComponent(name));

                formBody.append('=');

                formBody.append(encodeURIComponent(element.value));

                formBody.append('&');

            }

        }

        if (this._additionalInput) {

            formBody.append(this._additionalInput);

            this._additionalInput = null;

        }

        

        var request = new Sys.Net.WebRequest();

        var action = form.action;

        if (Sys.Browser.agent === Sys.Browser.InternetExplorer) {

            var queryIndex = action.indexOf('?');

            if (queryIndex !== -1) {

                var path = action.substr(0, queryIndex);

                if (path.indexOf("%") === -1) {

                    action = encodeURI(path) + action.substr(queryIndex);

                }

            }

            else if (action.indexOf("%") === -1) {

                action = encodeURI(action);

            }

        }

        request.set_url(action);

        request.get_headers()['X-MicrosoftAjax'] = 'Delta=true';

        request.get_headers()['Cache-Control'] = 'no-cache';

        request.set_timeout(this._asyncPostBackTimeout);

        request.add_completed(Function.createDelegate(this, this._onFormSubmitCompleted));

        request.set_body(formBody.toString());

        var handler = this._get_eventHandlerList().getHandler("initializeRequest");

        if (handler) {

            var eventArgs = new Sys.WebForms.InitializeRequestEventArgs(request, this._postBackSettings.sourceElement);

            handler(this, eventArgs);

            continueSubmit = !eventArgs.get_cancel();

        }

        if (!continueSubmit) {

            if (evt) {

                evt.preventDefault();

            }

            return;

        }

        this._scrollPosition = this._getScrollPosition();

        this.abortPostBack();

        handler = this._get_eventHandlerList().getHandler("beginRequest");

        if (handler) {

            var eventArgs = new Sys.WebForms.BeginRequestEventArgs(request, this._postBackSettings.sourceElement);

            handler(this, eventArgs);

        }

        

        if (this._originalDoCallback) {

            this._cancelPendingCallbacks();

        }

        this._request = request;

        request.invoke();

        if (evt) {

            evt.preventDefault();

        }

    }

我们可以发现AJAX回发所提交的数据量其实跟普通回发过程中提交的数据量是一样的，并且还附加了一些额外信息。

 

3.2 服务器端的处理

 

AJAX回发请求到达服务器之后，当前页面的生命周期跟普通回发引起的请求是一样的，页面的Init、Load和Render等等事件都会被触发，差别只是在于AJAX回发使用了不同的呈现画法。

 

AJAX回发引起的请求生命周期：

 

从上图我们可以看到，页面的生命周期与普通回发是一样的，同样页面上的控件也会经历相应的生命周期。

先了解一下ScriptManager控件在服务器端的处理：

 

- OnInit：在Init事件中，ScriptManager控件会注册页面的InitComplete, PreRenderComplete以及PreRender事件，另外还会根据本次请求的HTTP头来设定一个标记以确定本次回发是否为Ajax异步更新所引起的回发。

 

见下面的代码：

protected internal override void OnInit(EventArgs e)

{

    base.OnInit(e);

    if (this.EnableHistory)

    {

        this.RegisterAsyncPostBackControl(this);

    }

    if (!base.DesignMode)

    {

        IPage iPage = this.IPage;

        if (GetCurrent(this.Page) != null)

        {

            throw new InvalidOperationException(AtlasWeb.ScriptManager_OnlyOneScriptManager);

        }

        iPage.Items[typeof(IScriptManager)] = this;

        iPage.Items[typeof(ScriptManager)] = this;

        iPage.InitComplete += new EventHandler(this.OnPageInitComplete);

        iPage.PreRenderComplete += new EventHandler(this.OnPagePreRenderComplete);

        if (iPage.IsPostBack)

        {

            this._isInAsyncPostBack = PageRequestManager.IsAsyncPostBackRequest(iPage.Request.Headers);

            if (this.EnableHistory)

            {

                this._isNavigating = iPage.Request["__EVENTTARGET"] == this.UniqueID;

            }

        }

        this.PageRequestManager.OnInit();

        iPage.PreRender += new EventHandler(this.ScriptControlManager.OnPagePreRender);

    }

}

 

- OnPagePreRenderComplete，在PagePreRenderComplete事件中，ScriptManager控件会注册脚本文件以及Services代理脚本，MicrosoftAjax.js和MicrosoftAjaxWebForm.js就是在这个阶段被注册到客户端的。

 

见下面的代码：

private void OnPagePreRenderComplete(object sender, EventArgs e)

{

    if (!this.IsInAsyncPostBack)

    {

        if (this.SupportsPartialRendering)

        {

            this.IPage.ClientScript.GetPostBackEventReference(new PostBackOptions(this, null, null, false, false, false, false, true, null));

        }

        this.RegisterGlobalizationScriptBlock();

        this.RegisterScripts();

        this.RegisterServices();

        if (this.EnableHistory)

        {

            JavaScriptSerializer serializer = JavaScriptSerializer.CreateInstance();

            string[] strArray = new string[] { "\r\nSys.Application.setServerId(", serializer.Serialize(this.ClientID), ", ", serializer.Serialize(this.UniqueID), ");\r\n", ((this._initialState != null) && (this._initialState.Count != 0)) ? ("  Sys.Application.setServerState('" + this.GetStateString() + "');\r\n") : "\r\n" };

            string script = string.Concat(strArray);

            RegisterStartupScript(this, typeof(ScriptManager), "HistoryStartup", script, true);

        }

    }

    else

    {

        this.RegisterScripts();

        if (this.EnableHistory)

        {

            if ((this._initialState != null) && (this._initialState.Count == 0))

            {

                this._initialState = null;

            }

            if (this._newPointCreated)

            {

                this.RegisterDataItem(this, "'" + this.GetStateString() + "'", true);

            }

        }

    }

}

 

- OnPreRender，在PreRender事件中如果判定本次回发为AJAX回发，则会调用PageRequestManager对象的OnPreRender方法。而PageRequestManager对象则会调用Page对象的SetRenderMethodDelegate方法来代理Page的画法，PageRequestManager对象会真正负责本次AJAX回发最终的HTML代码。

见下面的代码：

 

public class ScriptManager : Control, 

{

   protected internal override void OnPreRender(EventArgs e)

   {

       base.OnPreRender(e);

       if (this.IsInAsyncPostBack)

       {

           this.PageRequestManager.OnPreRender();

       }

   }

}



internal sealed class PageRequestManager

{

   internal void OnPreRender()

   {

        this._owner.IPage.SetRenderMethodDelegate(new RenderMethod(this.RenderPageCallback));

   }

}

 

PageRequestManager的RenderPageCallback方法最终处理了AJAX回发所需要的HTML代码，在这个方法中会遍历页面上所有涉及到的UpdatePanel控件，得到其更新后的HTML代码后，与隐藏字段还有一些额外信息一起打包，然后传递给客户端。

 

见下面的代码：

private void RenderPageCallback(HtmlTextWriter writer, Control pageControl)

{

    this.ProcessUpdatePanels();

    IHttpResponse response = this._owner.IPage.Response;

    response.ContentType = "text/plain";

    response.Cache.SetNoServerCaching();

    IHtmlForm form = this._owner.IPage.Form;

    form.SetRenderMethodDelegate(new RenderMethod(this.RenderFormCallback));

    this._updatePanelWriter = writer;

    ParserStringWriter writer2 = new ParserStringWriter();

    ParserHtmlTextWriter writer3 = new ParserHtmlTextWriter(writer2);

    writer2.ParseWrites = true;

    form.RenderControl(writer3);

    writer2.ParseWrites = false;

    foreach (KeyValuePair<string, string> pair in writer2.HiddenFields)

    {

        if (ControlUtil.IsBuiltInHiddenField(pair.Key))

        {

            EncodeString(writer, "hiddenField", pair.Key, pair.Value);

        }

    }

    EncodeString(writer, "asyncPostBackControlIDs", string.Empty, this.GetAsyncPostBackControlIDs(false));

    EncodeString(writer, "postBackControlIDs", string.Empty, this.GetPostBackControlIDs(false));

    EncodeString(writer, "updatePanelIDs", string.Empty, this.GetAllUpdatePanelIDs());

    EncodeString(writer, "childUpdatePanelIDs", string.Empty, this.GetChildUpdatePanelIDs());

    EncodeString(writer, "panelsToRefreshIDs", string.Empty, this.GetRefreshingUpdatePanelIDs());

    EncodeString(writer, "asyncPostBackTimeout", string.Empty, this._owner.AsyncPostBackTimeout.ToString(CultureInfo.InvariantCulture));

    if (writer3.FormAction != null)

    {

        EncodeString(writer, "formAction", string.Empty, writer3.FormAction);

    }

    if (this._owner.IPage.Header != null)

    {

        string title = this._owner.IPage.Title;

        if (!string.IsNullOrEmpty(title))

        {

            EncodeString(writer, "pageTitle", string.Empty, title);

        }

    }

    this.RenderDataItems(writer);

    this.ProcessScriptRegistration(writer);

    this.ProcessFocus(writer);

}

 

3.3 客户端更新

当服务器端相应完毕后，客户端会得到响应信息，然后调用客户端对象PageRequestManager的_onFormSubmitCompleted方法来进行页面局部更新，最终会调用_updatePanel方法来更新UpdatePanel控件。

 

参见_onFormSubmitCompleted方法的代码：

 

function Sys$WebForms$PageRequestManager$_onFormSubmitCompleted(sender, eventArgs) {

        this._processingRequest = true;

        var delimitByLengthDelimiter = '|';

        if (sender.get_timedOut()) {

            this._endPostBack(this._createPageRequestManagerTimeoutError(), sender);

            return;

        }

        if (sender.get_aborted()) {

            this._endPostBack(null, sender);

            return;

        }

        if (!this._request || sender.get_webRequest() !== this._request) {

            return;

        }

        var errorMessage;

        var delta = [];

        if (sender.get_statusCode() !== 200) {

            this._endPostBack(this._createPageRequestManagerServerError(sender.get_statusCode()), sender);

            return;

        }

        var reply = sender.get_responseData();

        var delimiterIndex, len, type, id, content;

        var replyIndex = 0;

        var parserErrorDetails = null;

        while (replyIndex < reply.length) {

            delimiterIndex = reply.indexOf(delimitByLengthDelimiter, replyIndex);

            if (delimiterIndex === -1) {

                parserErrorDetails = this._findText(reply, replyIndex);

                break;

            }

            len = parseInt(reply.substring(replyIndex, delimiterIndex), 10);

            if ((len % 1) !== 0) {

                parserErrorDetails = this._findText(reply, replyIndex);

                break;

            }

            replyIndex = delimiterIndex + 1;

            delimiterIndex = reply.indexOf(delimitByLengthDelimiter, replyIndex);

            if (delimiterIndex === -1) {

                parserErrorDetails = this._findText(reply, replyIndex);

                break;

            }

            type = reply.substring(replyIndex, delimiterIndex);

            replyIndex = delimiterIndex + 1;

            delimiterIndex = reply.indexOf(delimitByLengthDelimiter, replyIndex);

            if (delimiterIndex === -1) {

                parserErrorDetails = this._findText(reply, replyIndex);

                break;

            }

            id = reply.substring(replyIndex, delimiterIndex);

            replyIndex = delimiterIndex + 1;

            if ((replyIndex + len) >= reply.length) {

                parserErrorDetails = this._findText(reply, reply.length);

                break;

            }

            content = reply.substr(replyIndex, len);

            replyIndex += len;

            if (reply.charAt(replyIndex) !== delimitByLengthDelimiter) {

                parserErrorDetails = this._findText(reply, replyIndex);

                break;

            }

            replyIndex++;

            Array.add(delta, {type: type, id: id, content: content});

        }

        if (parserErrorDetails) {

            this._endPostBack(this._createPageRequestManagerParserError(String.format(Sys.WebForms.Res.PRM_ParserErrorDetails, parserErrorDetails)), sender);

            return;

        }

        var updatePanelNodes = [];

        var hiddenFieldNodes = [];

        var arrayDeclarationNodes = [];

        var scriptBlockNodes = [];

        var scriptStartupNodes = [];

        var expandoNodes = [];

        var onSubmitNodes = [];

        var dataItemNodes = [];

        var dataItemJsonNodes = [];

        var scriptDisposeNodes = [];

        var asyncPostBackControlIDsNode, postBackControlIDsNode,

            updatePanelIDsNode, asyncPostBackTimeoutNode,

            childUpdatePanelIDsNode, panelsToRefreshNode, formActionNode;

        for (var i = 0; i < delta.length; i++) {

            var deltaNode = delta[i];

            switch (deltaNode.type) {

                case "updatePanel":

                    Array.add(updatePanelNodes, deltaNode);

                    break;

                case "hiddenField":

                    Array.add(hiddenFieldNodes, deltaNode);

                    break;

                case "arrayDeclaration":

                    Array.add(arrayDeclarationNodes, deltaNode);

                    break;

                case "scriptBlock":

                    Array.add(scriptBlockNodes, deltaNode);

                    break;

                case "scriptStartupBlock":

                    Array.add(scriptStartupNodes, deltaNode);

                    break;

                case "expando":

                    Array.add(expandoNodes, deltaNode);

                    break;

                case "onSubmit":

                    Array.add(onSubmitNodes, deltaNode);

                    break;

                case "asyncPostBackControlIDs":

                    asyncPostBackControlIDsNode = deltaNode;

                    break;

                case "postBackControlIDs":

                    postBackControlIDsNode = deltaNode;

                    break;

                case "updatePanelIDs":

                    updatePanelIDsNode = deltaNode;

                    break;

                case "asyncPostBackTimeout":

                    asyncPostBackTimeoutNode = deltaNode;

                    break;

                case "childUpdatePanelIDs":

                    childUpdatePanelIDsNode = deltaNode;

                    break;

                case "panelsToRefreshIDs":

                    panelsToRefreshNode = deltaNode;

                    break;

                case "formAction":

                    formActionNode = deltaNode;

                    break;

                case "dataItem":

                    Array.add(dataItemNodes, deltaNode);

                    break;

                case "dataItemJson":

                    Array.add(dataItemJsonNodes, deltaNode);

                    break;

                case "scriptDispose":

                    Array.add(scriptDisposeNodes, deltaNode);

                    break;

                case "pageRedirect":

                    if (Sys.Browser.agent === Sys.Browser.InternetExplorer) {

                        var anchor = document.createElement("a");

                        anchor.style.display = 'none';

                        anchor.attachEvent("onclick", cancelBubble);

                        anchor.href = deltaNode.content;

                        document.body.appendChild(anchor);

                        anchor.click();

                        anchor.detachEvent("onclick", cancelBubble);

                        document.body.removeChild(anchor);

                        

                        function cancelBubble(e) {

                            e.cancelBubble = true;

                        }

                    }

                    else {

                        window.location.href = deltaNode.content;

                    }

                    return;

                case "error":

                    this._endPostBack(this._createPageRequestManagerServerError(Number.parseInvariant(deltaNode.id), deltaNode.content), sender);

                    return;

                case "pageTitle":

                    document.title = deltaNode.content;

                    break;

                case "focus":

                    this._controlIDToFocus = deltaNode.content;

                    break;

                default:

                    this._endPostBack(this._createPageRequestManagerParserError(String.format(Sys.WebForms.Res.PRM_UnknownToken, deltaNode.type)), sender);

                    return;

            }

        }

        var i;

        if (asyncPostBackControlIDsNode && postBackControlIDsNode &&

            updatePanelIDsNode && panelsToRefreshNode &&

            asyncPostBackTimeoutNode && childUpdatePanelIDsNode) {

            this._oldUpdatePanelIDs = this._updatePanelIDs;

            var childUpdatePanelIDsString = childUpdatePanelIDsNode.content;

            this._childUpdatePanelIDs = childUpdatePanelIDsString.length ? childUpdatePanelIDsString.split(',') : [];

            var asyncPostBackControlIDsArray = this._splitNodeIntoArray(asyncPostBackControlIDsNode);

            var postBackControlIDsArray = this._splitNodeIntoArray(postBackControlIDsNode);

            var updatePanelIDsArray = this._splitNodeIntoArray(updatePanelIDsNode);

            this._panelsToRefreshIDs = this._splitNodeIntoArray(panelsToRefreshNode);

            for (i = 0; i < this._panelsToRefreshIDs.length; i++) {

                var panelClientID = this._uniqueIDToClientID(this._panelsToRefreshIDs[i]);

                if (!document.getElementById(panelClientID)) {

                    this._endPostBack(Error.invalidOperation(String.format(Sys.WebForms.Res.PRM_MissingPanel, panelClientID)), sender);

                    return;

                }

            }

            var asyncPostBackTimeout = asyncPostBackTimeoutNode.content;

            this._updateControls(updatePanelIDsArray, asyncPostBackControlIDsArray, postBackControlIDsArray, asyncPostBackTimeout);

        }

        this._dataItems = {};

        for (i = 0; i < dataItemNodes.length; i++) {

            var dataItemNode = dataItemNodes[i];

            this._dataItems[dataItemNode.id] = dataItemNode.content;

        }

        for (i = 0; i < dataItemJsonNodes.length; i++) {

            var dataItemJsonNode = dataItemJsonNodes[i];

            this._dataItems[dataItemJsonNode.id] = Sys.Serialization.JavaScriptSerializer.deserialize(dataItemJsonNode.content);

        }

        var handler = this._get_eventHandlerList().getHandler("pageLoading");

        if (handler) {

            handler(this, this._getPageLoadingEventArgs());

        }

        if (formActionNode) {

            this._form.action = formActionNode.content;

        }

        

        

        Sys._ScriptLoader.readLoadedScripts();

        Sys.Application.beginCreateComponents();

        var scriptLoader = Sys._ScriptLoader.getInstance();

        this._queueScripts(scriptLoader, scriptBlockNodes, true, false);

        

        this._updateContext = {

            response: sender,

            updatePanelNodes: updatePanelNodes,

            scriptBlockNodes: scriptBlockNodes,

            scriptDisposeNodes: scriptDisposeNodes,

            hiddenFieldNodes: hiddenFieldNodes,

            arrayDeclarationNodes: arrayDeclarationNodes,

            expandoNodes: expandoNodes,

            scriptStartupNodes: scriptStartupNodes,

            onSubmitNodes: onSubmitNodes

        };

        scriptLoader.loadScripts(0,

            Function.createDelegate(this, this._scriptIncludesLoadComplete),

            Function.createDelegate(this, this._scriptIncludesLoadFailed),

            null);

}

 

4．结语

 

使用UpdatePanel是给已经存在的ASP.NET应用程序添加AJAX体验的最快捷方式，对于应用程序的架构也不会有影响，我们可以使用它来逐步的提高应用程序的用户体验。但是其性能与纯粹的AJAX方式相比较，还是比较差的。