/** * This class serves as the superclass for all xml-http request objects supported by * the Environment. *

* Important Notes: *

* In order to obtain a new XmlHttpRequest object for the platform * on which your application is running, do not directly create an object from classes that * extend this object. directly. Instead, * call the static method self.Environment.getNewXmlHttpRequest. *
* Modify the method Environment_init_getXmlHttpConstructor (an inner method * of the init method of the Environment object) to support * any new classes that extend this class (AbstractXmlHttpRequest). *
* In order to send a message, do not create a new XmlHttpRequest object. Instead, * call the send method on an object of the Messenger datatype. *

*
* This class serves to augment the standard XmlHttpRequest * object that is built-in to some web browsers. It adds an i.d. and * a unique onreadystatechange * event handler method. While * this class hiearchy gives great flexibility, please note that it is actually * necessitated by the immutability of the XmlHttpRequest object from * Microsoft(tm), which is an 'ActiveX' object. Otherwise, we could add the properties we * need with a simple augmentor-method. *

* Ellen Hudson-Snyder, * Elvin Vedar, * Christopher M. Balz. *

CVS Version Info:
* $Id: AbstractXmlHttpRequest.js,v 1.5 2005/12/09 05:54:53 evedar Exp $ *
* @emits-event onreadystatechange This event is emitted by the xml-http request object that is * held as a property of this object. The event travels as * emitted from this object. * @class-prop number intReadyState The integer value that signifies the completed * state of an asynchronous xml-http request. * @class-prop number intUniqueNum This variable is used to create a unique serial * number for every object created from concrete classes of this class. * @object-prop string strId The i.d. of the class. * @object-prop number intSerialNumber The serial number of a given object made from * this class. * @object-prop string strRequestUri The uri used by this request object. It is meant * to point to a requested resource (for example, an xml file on a server). * @object-prop string strMethod The http protocol method used to make the request. * @object-prop boolean booAsynchronous Whether or not the request to be made should be * asynchronous or not. * @object-prop objXmlHttpRequest The xml-http request object held by instances of this class. * @author Team GigaToasted (Fall-2005-CMU-NASA/Google-Practicum Subteam) * @version 1.0 */ self.AbstractXmlHttpRequest.intReadyState = 4; self.AbstractXmlHttpRequest.intUniqueNum = 0; /** * Creates a new AbstractXmlHttpRequest object. */ function AbstractXmlHttpRequest() { // Properties: this.strId = "CrossBrowserXMLHttpRequest"; this.intSerialNumber = -1; this.strRequestUri = ""; this.strMethod = "get"; // Default value. this.booAsynchronous = true; // Default value. // Methods: this.superC = AbstractXmlHttpRequest_superConstructor; this.send = AbstractXmlHttpRequest_send; } /** * Perform instance-specific initialization of the object instance made from the extending * class. *

Details:

* In this method, we use var to capture the value of

strId 
 * and objXmlHttpRequest
 * in the function closure onreadystatechange, below.  For some odd reason,
 * the this context does not work in the onreadystatechange method
 * (i.e., as it does work in dom event handlers).


 * The Messenger object registers to listen to events from all objects of 
 * this type, so we give all objects the same strId value.  
 * @param pObjXmlHttpRequest Object The xml-http request object held by the instance.
 * @param pStrRequestUri string The uri pointing to the 
 *                       requested resource (for example, an xml file on a server).
 * @param pStrMethod string OPTIONAL, MAY BE null Either 'get' or 'post'. Defaults to
 *                   'get'.
 * @param pBooAsynchronous boolean OPTIONAL, MAY BE null Whether or
 *                          not the request is to be asynchronous.  Defaults to 'true'.
 */
function AbstractXmlHttpRequest_superConstructor(pObjXmlHttpRequest, pStrRequestUri, pStrMethod,  
                                                 pBooAsynchronous) {
    var objXmlHttpRequest = this.objXmlHttpRequest = pObjXmlHttpRequest, strId = this.strId,
        intArgs = arguments.length;

    this.intSerialNumber = self.AbstractXmlHttpRequest.intUniqueNum++;       

    this.strRequestUri = pStrRequestUri;
    
    if (intArgs > 2) {
        if (pStrMethod != null) {
            this.strMethod = pStrMethod;
        }
    }

    if (intArgs > 3) {
        if (pBooAsynchronous != null) {
            this.booAsynchronous = pBooAsynchronous;
        }
    }    

    this.objXmlHttpRequest.onreadystatechange = function() {
        if (objXmlHttpRequest.readyState == self.AbstractXmlHttpRequest.intReadyState) {
            self.Environment.handleEvent(strId, 'onreadystatechange', null);
        }
    }
}


/**
 * This convenience method opens and sends the xml-http request.
 * @param pObjMessage Object  MAY BE null This parameter is required by the XmlHttp 
 *                    object.
 */
function AbstractXmlHttpRequest_send(pObjMessage) {
    this.objXmlHttpRequest.open(this.strMethod, this.strRequestUri, this.booAsynchronous);
    this.objXmlHttpRequest.send(pObjMessage);
}