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Synchronous page method call in ASP.NET AJAX library

Posted by Dmytro Shteflyuk on under ASP.NET

Sometimes we need to do some tasks, that libraries developers even have not foreseen. One of such cases is to make synchronous AJAX call (Asynchronous JavaScript And XML). Below you could find quick solution.

Please note: my solution is just copy/past of the XmlHttpExecutor code with two small changes:

  • I have passed false as third parameter of the XMLHttpRequest.open method to make synchronous call.
  • I have cached request results in XMLHttpSyncExecutor members before freeing XMLHttpRequest in the _onReadyStateChange function.

So let’s get started. First of all we would define XMLHttpSyncExecutor class, descendant of the WebRequestExecutor.

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Type.registerNamespace('Sys.Net');

Sys.Net.XMLHttpSyncExecutor = function()
{
    if (arguments.length !== 0) throw Error.parameterCount();
    Sys.Net.XMLHttpSyncExecutor.initializeBase(this);

    var _this = this;
    this._xmlHttpRequest = null;
    this._webRequest = null;
    this._responseAvailable = false;
    this._timedOut = false;
    this._timer = null;
    this._aborted = false;
    this._started = false;

    this._responseData = null;
    this._statusCode = null;
    this._statusText = null;
    this._headers = null;

    this._onReadyStateChange = function () {
        if (_this._xmlHttpRequest.readyState === 4 ) {
            _this._clearTimer();
            _this._responseAvailable = true;

            _this._responseData = _this._xmlHttpRequest.responseText;
            _this._statusCode = _this._xmlHttpRequest.status;
            _this._statusText = _this._xmlHttpRequest.statusText;
            _this._headers = _this._xmlHttpRequest.getAllResponseHeaders();

            _this._webRequest.completed(Sys.EventArgs.Empty);
            if (_this._xmlHttpRequest != null) {
                _this._xmlHttpRequest.onreadystatechange = Function.emptyMethod;
                _this._xmlHttpRequest = null;
            }
        }
    }

    this._clearTimer = function this$_clearTimer() {
        if (_this._timer != null) {
            window.clearTimeout(_this._timer);
            _this._timer = null;
        }
    }

    this._onTimeout = function this$_onTimeout() {
        if (!_this._responseAvailable) {
            _this._clearTimer();
            _this._timedOut = true;
            _this._xmlHttpRequest.onreadystatechange = Function.emptyMethod;
            _this._xmlHttpRequest.abort();
            _this._webRequest.completed(Sys.EventArgs.Empty);
            _this._xmlHttpRequest = null;
        }
    }
}

This is very simple and clean, so I’ll just show you other methods of the XMLHttpSyncExecutor.

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function Sys$Net$XMLHttpSyncExecutor$get_timedOut() {
    /// <value type="Boolean"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    return this._timedOut;
}

function Sys$Net$XMLHttpSyncExecutor$get_started() {
    /// <value type="Boolean"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    return this._started;
}

function Sys$Net$XMLHttpSyncExecutor$get_responseAvailable() {
    /// <value type="Boolean"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    return this._responseAvailable;
}

function Sys$Net$XMLHttpSyncExecutor$get_aborted() {
    /// <value type="Boolean"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    return this._aborted;
}

function Sys$Net$XMLHttpSyncExecutor$executeRequest() {
    if (arguments.length !== 0) throw Error.parameterCount();
    this._webRequest = this.get_webRequest();

    if (this._started) {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallOnceStarted, 'executeRequest'));
    }
    if (this._webRequest === null) {
        throw Error.invalidOperation(Sys.Res.nullWebRequest);
    }

    var body = this._webRequest.get_body();
    var headers = this._webRequest.get_headers();
    this._xmlHttpRequest = new XMLHttpRequest();
    this._xmlHttpRequest.onreadystatechange = this._onReadyStateChange;
    var verb = this._webRequest.get_httpVerb();
    this._xmlHttpRequest.open(verb, this._webRequest.getResolvedUrl(), false); // False to call Synchronously
    if (headers) {
        for (var header in headers) {
            var val = headers[header];
            if (typeof(val) !== "function")
                this._xmlHttpRequest.setRequestHeader(header, val);
        }
    }

    if (verb.toLowerCase() === "post") {
        if ((headers === null) || !headers['Content-Type']) {
            this._xmlHttpRequest.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        }

        if (!body) {
            body = "";
        }
    }

    var timeout = this._webRequest.get_timeout();
    if (timeout > 0) {
        this._timer = window.setTimeout(Function.createDelegate(this, this._onTimeout), timeout);
    }
    this._xmlHttpRequest.send(body);
    this._started = true;
}

 function Sys$Net$XMLHttpSyncExecutor$getAllResponseHeaders() {
    /// <returns type="String"></returns>
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._responseAvailable) {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallBeforeResponse, 'getAllResponseHeaders'));
    }

    return this._headers;
}

function Sys$Net$XMLHttpSyncExecutor$get_responseData() {
    /// <value type="String"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._responseAvailable)
    {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallBeforeResponse, 'get_responseData'));
    }

    return this._responseData;
}

function Sys$Net$XMLHttpSyncExecutor$get_statusCode() {
    /// <value type="Number"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._responseAvailable)
    {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallBeforeResponse, 'get_statusCode'));
    }

    return this._statusCode;
}

function Sys$Net$XMLHttpSyncExecutor$get_statusText() {
    /// <value type="String"></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._responseAvailable)
    {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallBeforeResponse, 'get_statusText'));
    }

    return this._statusText;
}

function Sys$Net$XMLHttpSyncExecutor$get_xml() {
    /// <value></value>
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._responseAvailable)
    {
        throw Error.invalidOperation(String.format(Sys.Res.cannotCallBeforeResponse, 'get_xml'));
    }

    var xml = this._responseData;
    if ((!xml) || (!xml.documentElement))
    {
        xml = new XMLDOM(this._responseData);
        if ((!xml) || (!xml.documentElement))
        {
            return null;
        }
    }
    else if (navigator.userAgent.indexOf('MSIE') !== -1)
    {
        xml.setProperty('SelectionLanguage', 'XPath');
    }

    if ((xml.documentElement.namespaceURI === "http://www.mozilla.org/newlayout/xml/parsererror.xml") &&
        (xml.documentElement.tagName === "parsererror"))
    {
        return null;
    }

    if (xml.documentElement.firstChild && xml.documentElement.firstChild.tagName === "parsererror")
    {
        return null;
    }

    return xml;
}

function Sys$Net$XMLHttpSyncExecutor$abort() {
    if (arguments.length !== 0) throw Error.parameterCount();
    if (!this._started) {
        throw Error.invalidOperation(Sys.Res.cannotAbortBeforeStart);
    }

    if (this._aborted || this._responseAvailable || this._timedOut)
        return;

    this._aborted = true;

    this._clearTimer();

    if (this._xmlHttpRequest && !this._responseAvailable) {
        this._xmlHttpRequest.onreadystatechange = Function.emptyMethod;
        this._xmlHttpRequest.abort();

        this._xmlHttpRequest = null;
        var handler = this._webRequest._get_eventHandlerList().getHandler("completed");
        if (handler) {
            handler(this, Sys.EventArgs.Empty);
        }
    }
}

Sys.Net.XMLHttpSyncExecutor.prototype = {
    get_timedOut: Sys$Net$XMLHttpSyncExecutor$get_timedOut,
    get_started: Sys$Net$XMLHttpSyncExecutor$get_started,
    get_responseAvailable: Sys$Net$XMLHttpSyncExecutor$get_responseAvailable,
    get_aborted: Sys$Net$XMLHttpSyncExecutor$get_aborted,
    executeRequest: Sys$Net$XMLHttpSyncExecutor$executeRequest,
    getAllResponseHeaders: Sys$Net$XMLHttpSyncExecutor$getAllResponseHeaders,
    get_responseData: Sys$Net$XMLHttpSyncExecutor$get_responseData,
    get_statusCode: Sys$Net$XMLHttpSyncExecutor$get_statusCode,
    get_statusText: Sys$Net$XMLHttpSyncExecutor$get_statusText,
    get_xml: Sys$Net$XMLHttpSyncExecutor$get_xml,
    abort: Sys$Net$XMLHttpSyncExecutor$abort
}
Sys.Net.XMLHttpSyncExecutor.registerClass('Sys.Net.XMLHttpSyncExecutor', Sys.Net.WebRequestExecutor);

And finally we will notify ASP.NET AJAX that script have been loaded.

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if (typeof(Sys) != 'undefined')
{
    Sys.Application.notifyScriptLoaded();
}

Usage is not so simple as wanted, but it’s still quite easy to understand:

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function getServerTime() {
    // Instantiate a WebRequest.
    var wRequest = new Sys.Net.WebRequest();
    // Set the request URL.
    wRequest.set_url(PageMethods.get_path() + "/GetServerTime");
    // Set the request verb.
    wRequest.set_httpVerb('POST');
   
    wRequest.get_headers()['Content-Type'] = 'application/json; charset=utf-8';

    var executor = new Sys.Net.XMLHttpSyncExecutor();
    wRequest.set_executor(executor);
    // Execute the request.
    wRequest.invoke();

    if (executor.get_responseAvailable()) {
        return executor.get_object();
    }
    return false;
}

When you are using ScriptService, you will not see these difficulties, because ASP.NET will generate wrappers by itself. But if you need synchronous AJAX call — sorry, but in this case you should do it manually. Sample solution could be found here.

10 Responses to this entry

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Kigorw
said on September 14th, 2007 at 00:17 · Permalink

“Один из таких случаев — выполнение синхронного AJAX-вызова (Asynchronous JavaScript And XML — Асинхронный JavaScript и XML).” – прикольно фраза смотрится.

Что за случай, интересно?

Kigorw
said on September 14th, 2007 at 00:19 · Permalink

хотя может и полезно в случае если не хочется с колбеками связываться…

Dmytro Shteflyuk
said on September 14th, 2007 at 00:32 · Permalink

Угу, синхронный асинхронный вызов :-) Хотел обыграть как игру слов, но инглиша не хватило.

А случай простой. Перед отправкой формы (на onsubmit или клиентский onclick у кнопки) нужно получить с сервера некоторый ключ someCode, который использовать для обработки данных формы (в частности захэшировать md5(fieldValue+someCode)) и продолжить выполнение стандартного кода, который генерит ASP.NET (валидации там всякие и постбек). Муторно описал в общем, но задача есть.

Решить ее же можно по-другому (через AJAX) – на onclick кнопки повесить вызов AJAX и return false;, а в колбеке вставить код, который вызовет валидацию и сделает постбек (ClientScript.GetPostBackEventReference), но решение не очень универсальное. С синхронным вызовом все проще — получил код, а дальше пусть само как обычно работает.

Nicola
said on January 25th, 2008 at 13:24 · Permalink

Hi
Your post was very helpful to me thanks.
I have only one problem.
My PageMethod has a parameter.
How do you pass it ?
I tried

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wRequest.set_url(PageMethods.get_path() + "/RunQuery("+JSON.stringify(Param)+")");

or

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Sys.Net.WebServiceProxy.invoke('/Default.aspx', 'RunQuery', false, { Params: JSON.stringify(sSQL) }, null, OnErrorQuery);

but they both don’t work ..
Thanks in advance for any help / idea
Bye
Nicola

Dmytro Shteflyuk
said on January 25th, 2008 at 14:59 · Permalink

Hi Nicola,

If you want to use URL params (GET), try this:

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var urlParams = {'param1':'value'};
wRequest.set_url(Sys.Net.WebRequest._createUrl(PageMethods.get_path()+"/RunQuery", urlParams));

But as I understand from your code, you need POST, so

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var params = {'param1':'value'};
var body = Sys.Serialization.JavaScriptSerializer.serialize(params);
wRequest.set_body(body);
Nicola
said on January 25th, 2008 at 15:43 · Permalink

Hi Dmitro,

Yes I need POST parameter.
It works !!
Thank you very much
Das vidanje!
Nicola

emiliano
said on March 4th, 2008 at 10:45 · Permalink

hi,
I used your solution but it doesn’t work with firefox.
The strange is that, if I install the Add-on firebug it work, but if I disable firebug no.

Mehmet
said on June 23rd, 2008 at 12:57 · Permalink

In

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function Sys$Net$XMLHttpSyncExecutor$executeRequest() {

at the end, before

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    this._started = true;

insert

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    if (navigator.appName != "Microsoft Internet Explorer" && navigator.appName != "Opera" && navigator.appVersion.indexOf('Safari') < 0)
    {
        this._onReadyStateChange(this._xmlHttpRequest);
    }
sheich
said on January 20th, 2009 at 18:58 · Permalink

Mehmet, thank you a lot!

Remi Bourgarel
said on February 13th, 2009 at 12:53 · Permalink

Merci beaucoup

You save me a lot of time.

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