here is some content. This is
AJAX In Action [119]
to be cleared and replaced by a low-level notification if everything went okay or by a medium-level notification if there was an error.
To implement this, we simply need to create Message objects at appropriate points in the lifecycle of the request, such as when the request is fired, when it completes or errors, and so on. The modified code for our ContentLoader object is given in listing 6.9.
Listing 6.9 ContentLoader with notifications
net.ContentLoader=function( ... ){ ... };
net.ContentLoader.msgId=1;
net.ContentLoader.prototype={
loadXMLDoc:function(url,method,params,contentType){
if (!method){
method="GET";
}
if (!contentType && method=="POST"){
contentType='application/x-www-form-urlencoded';
}
if (window.XMLHttpRequest){
this.req=new XMLHttpRequest();
} else if (window.ActiveXObject){
this.req=new ActiveXObject("Microsoft.XMLHTTP");
}
if (this.req){
try{
var loader=this;
this.req.onreadystatechange=function(){
loader.onReadyState.call(loader);
}
this.req.open(method,url,true);
if (contentType){
this.req.setRequestHeader('Content-Type', contentType);
Licensed to jonathan zheng 238 CHAPTER 6 The user experience } this.notification=new msg.Message( b Notify request has started "net00"+net.ContentLoader.msgId, "loading "+url, msg.PRIORITY_LOW.id, -1, "img/ball-earth.gif" ); net.ContentLoader.msgId++; this.req.send(params); }catch (err){ this.onerror.call(this); } } }, onReadyState:function(){ var req=this.req; var ready=req.readyState; if (ready==net.READY_STATE_COMPLETE){ var httpStatus=req.status; if (httpStatus==200 || httpStatus==0){ this.onload.call(this); this.notification.clear(); c Clear initial notification }else{ this.onerror.call(this); } } }, defaultError:function(){ d Notify on error var msgTxt="error fetching data!" +" +" +" +" if (this.notification){ this.notification.clear(); } this.notification=new msg.Message( "net_err00"+net.ContentLoader.msgId, msgTxt,msg.PRIORITY_DEFAULT.id ); net.ContentLoader.msgId++; } }; Licensed to jonathan zheng Using the framework with network requests 239 When we make a network request using loadXMLDoc(), we create a low-level notification b and attach a reference to it to the ContentLoader object. Note that we set the lifetime to -1, so that the notification won’t expire by itself. In the onReadyState() method, we clear the notification if everything has gone well c. In the case of an error, we call the defaultError() method, which now generates a notification of its own d. The message for this notification uses HTML markup to create a richer report than plain text could. Listing 6.10 demonstrates an example page using this modified ContentLoader. Listing 6.10 Notifications sample page "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> Licensed to jonathan zheng 240 CHAPTER 6 The user experience
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