Phonegap synchronous ajax call - javascript

I've been working with phonegap to build an app and have been using ajax to communicate with the server to get all the necessary data. Some of the pages take a few seconds to load (and I dont display the page until everything is loaded) and I would like a loading screen to appear while the client is communicating with the server and processing all the data.
I had everything working great until I decided to throw the the ajax calls into functions (I'm working with a few team members, so I thought it would be easier for them to use these ajax calls if they were in some nice functions). Now because of the ajax function is asynchronous, the loading screen turns on and off before the requests are finished processing. I would like my function to stop the execution of code (similar to an alert) so that the loading screen will turn off AFTER all the ajax calls are made.
Essentially I want my javascript code to look like this:
loading();
sendRequests();
notLoading();
where loading() displays the loading screen, and notLoading() turns the loading screen off. My sendRequests() function is specific to each page (each page has to send different requests depending on the functionality of the page)
if you guys are wondering what the loading() and notLoading() functions looks like, here you go
// functions to make loading screen appear and disappear
function loading() {
document.getElementById("blackout").style.display = 'block';
}
function notLoading() {
document.getElementById("blackout").style.display = 'none';
}
I looked into a few other posts about it
How to wait for ajax request to complete in javascript when synchronous option is not available?
http://www.hunlock.com/blogs/Snippets:_Synchronous_AJAX
Which those two links essentially tell you the same information, that the third parameter in request.open() needs to be set to false... well, I've tried that and it didn't work =/
here is an example of my getRequest() function so everyone can see what I'm trying to do:
// will send a GET request to the parameter url
function getRequest(url) {
var req = new XMLHttpRequest();
req.open('GET', url, false);
setHeaders(req);
req.onreadystatechange = function() {
if (req.readyState == 4) {
if( (req.status == 200) || (req.status == 0) ) {
if( (typeof req.responseText != "undefined") && (req.responseText != "") ) {
localStorage["request"] = req.responseText;
}
else {
alert("GR: Error talking to the server");
}
}
else {
alert("GR: Error talking to server");
}
}
}
req.send(null);
return parseJSON();
}
If anyone knows how I can fix this, I would be very appreciative!

I ended up just throwing the notLoading() function at all the exit statuses in the sendRequests() function. Kind of a pain, but seems to work now.

Related

Will an ajax call finish even after a page redirect?

I am trying to create a temporary image url for a local image and send it to Google to do a Search by Image. I don't want the image url to be permanent so I want to delete it right after I use it. I have the code below:
// Gets a URL that can be used to do a search by image through Google.
function getImageURL() {
var xml = new XMLHttpRequest();
xml.onreadystatechange = function () {
if (xml.readyState == 4 && xml.status == 200) {
deleteImageURL(); // asynchronous call to server to delete the URL
window.location.href =
"https://www.google.com/searchbyimage?site=search&sa=X&image_url="
+ xml.responseText; // the image url
}
}
xml.open("GET", "REST_ENDPOINT", true);
xml.send();
}
The function above calls the server, and when it finishes, will delete the url and redirect the page. The function "deleteImageURL()" is another ajax call done asynchronously. Currently, this loads the google page fine as the image URL is not done deleting the url by the time that the redirect happens.
My question is this: Will deleteImageURL() finish deleting the image URL even after the page redirects or will it stop (and thus, never delete the URL)?
EDIT: So I was thinking about what you guys were saying about race conditions and tried the following code instead:
// Gets a URL that can be used to do a search by image through Google.
function getImageURL() {
var xml = new XMLHttpRequest();
xml.onreadystatechange = function () {
if (xml.readyState == 4 && xml.status == 200) {
deleteImageURL(xml.responseText);
}
}
xml.open("GET", "REST_ENDPOINT"
+ id + "/public_url", true);
xml.send();
}
// Deletes the url for the image.
function deleteImageURL(imageURL) {
var xml = new XMLHttpRequest();
xml.open("GET", "REST_ENDPOINT_FOR_DELETE", true);
xml.send();
window.location.href =
"https://www.google.com/searchbyimage?site=search&sa=X&image_url="
+ imageURL;
}
This code works every time that I run it. I think that there still may be a race condition, but it seems to be working fine so far.
Thanks again.
The "deleteImageURL()" will finish deleting the image URL even after the page redirects..
Refer : Should I wait for ajax to complete to redirect a page?
The server won't stop processing the request (initiated by deleteImageUrl), but you will not be able to handle a callback if the current page unloads in the browser before the operation is completed.
If deleteImageURL(); contains an async call you should do the redirect when the call is completed. Your code will work when the call is synchronious. We don't see the source of deleteImageURL(); and can be more concrete, but you should do the same thing as you've done for getImageURL().

Making an ASP.NET MVC Ajax call with the use of Javascript

First off, thanks for taking the time to read.
I'm trying to delve into ASP.NET MVC at the moment, however i currently have no wish to use any type of JavaScript framework, so please, don't tell me how much easier it would be etc, in your answer.
I currently have a Javascript function that successfully makes an AJAX call, however i am struggling to understand why no values are being returned from the request.
The function is as follows.
function ajaxRequestUser(num) {
var ajax;
try {
ajax = new XMLHttpRequest();
} catch(e) {
try {
ajax = new ActiveXObject(Msxml2.XMLHTTP);
} catch(e){
alert('old browser');
}
}
ajax.readystatechange = function () {
if (ajax.readyState == 4) {
var queryResult = ajax.responseText;
if (!queryResult) {
alert('No Information.');
} else {
alert(queryResult);
}
}
}
var requestString = "?user="+num;
ajax.open("GET", "/Users/GetUser" + requestString, true);
ajax.send(null);
}
The function is called via a separate function that simply does some UI modifications to allow for the display of the data.
The alerts are there at this point, because i was not receiving any data back from the call and i was testing to see if that part of the code was being hit at all (Don't go into the differences between Synchronous and Asynchronous.). No matter how long i waited the data being returned was not being returned, after breaking through the actual server side c#, i saw the data being sent back, but it was just never being received. Is there something in the code that was done wrong? Or am i going about receiving the inbound data in the wrong way?
I have found the issue related to my code, and it is solely an error based around the declaration of my ajax.event where the event is onreadystatechange as opposed to readystatechange

Ajax Function Only Working Part of the Time

I am using the following Ajax function format:
var xmlhttp;
function addAddress(str)
{
if (window.XMLHttpRequest)
{
xmlhttp = new XMLHttpRequest();
}
else
{
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function()
{
if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
{
//specific selection text
document.getElementById('info').innerHTML = xmlhttp.responseText;
}
}
var addAddress = "add";
xmlhttp.open("POST", "sys.php", true);
xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
var queryString = "&addAddress=" + addAddress;
xmlhttp.send(queryString);
}
function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
{
return new XMLHttpRequest();
}
if (windows.ActiveXObject)
{
return new ActiveXObject("Micorsoft.XMLHTTP");
}
return null;
}
Up until now, all of my Ajax functions, like the one above, have been running fine. However, now the function will work only sometimes. Now, sometimes I will have to click the onclick event a couple times to execute the function or the function will just hang, and then after about 4 minutes it will execute.
I tested parts of the function and found that the issue lies some where at the:
if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
{
alert(xmlhttp.status);
//specific selection text
document.getElementById('info').innerHTML = xmlhttp.responseText;
}
When the function works, I can alert(xmlhttp.status) and get 200. However, when it's not working, the alert box doesn't even trigger. In fact, nothing happens, not even an error.
Could this be a server issue? I am kind of thinking my website got hacked, but I cannot find any issues accept that the Ajax functions are not executing properly.
Lastly, I do not get this problem on my localhost, it's only happening on the live website.
Any help will be greatly appreciated.
Thanks
First just confirm that the addAddress function is actually being called when you click the button or control that should trigger it.
Just a simple alert in the first line like this would work:
function addAddress(str)
{
alert('addAddress has been called!')
....
}
If you don't get the alert, make sure there isn't a javascript error on the page that is preventing the function from running. In firefox you press CTRL+SHIFT+J to see the error console for example.
If that part is working, trying putting the URL for the ajax request directly into your browser and diagnose it that way.
Looks like you are requesting this url with ajax:
sys.php&addAddress= (address goes here)
Check that the page will load directly in your browser. If not, the problem is not the ajax request, but something with the sys.php page itself - which you can then drill down on.
Hope that helps!
This wasn't the answer I was expecting, but I ended up having my web host (GoDaddy) change servers, and that resolved the problem. For almost a year, I was running IIS7 with PHP. Since I had never run into any problems, I just continued using that server. After the Ajax latency issue and not being able to figure out a solution, I figured I would just switch over to Apache. After the change, everything started running smoothly again.
I am thinking maybe there was a software update that I was not notified about. Or, maybe my website was getting hit with a DDoS, which was decreasing the performance of my Ajax requests. Lastly, maybe someone got into IIS and changed a setting. I don't know, all I know is that the minute the server was changed over to Apache was when the website started running normally again.
Thanks for everyone's suggestions.

Jquery mobile ajax loader image

I' m using this code in my mobile application built with phonegap and jQuery I want to show pictures from server but I couldn't integrate showPageLoadingMsg function and I 'm not convinced that this type of Ajax call is useful and powerful. So I want really know what type of Ajax call I should use and how to use showPageLoadingMsg() function in my Android phone application .
server = "http://monserveur.com/upload.php";
var wid = $(window).width();
if (server) {
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange=function(){
if(xmlhttp.readyState == 4){
alert('ready');
if (xmlhttp.status == 200 ) {
alert('200');
document.getElementById('ousa').innerHTML = xmlhttp.responseText;
}
else {
document.getElementById('ousa').innerHTML = "Error retrieving pictures from server.";
}
}
};
xmlhttp.open("GET", server+"?wid="+wid, true);
xmlhttp.send();
Have you tried
http://api.jquery.com/ajaxStart/
http://api.jquery.com/ajaxStop/
and couple them with a logic like found here
http://www.w3schools.com/jquery/ajax_ajaxstart.asp
$("div").ajaxStart(function(){
$(this).html("<img src='demo_wait.gif' />");
})ajaxStop(function(){
$(this).empty();
});
This will basically add a listener if added to a self executing function or the dom ready logic of your script this listener will wait for anything ajax related to run.
$.post()
$.get()
$.ajax()
$.getJSON()
$.postJSON()
//any I missed?
also I notice you mention phonegap, are you currently using the xhr.js they suggest using with AJAX requests? If not its something I suggest looking into, due to the same domain policy your AJAX may just be failing silently and very quickly. the xhr.js over comes the bounds of the same domain policy.

Comet (long polling) and XmlHttpRequest status

I'm playing around a little bit with raw XmlHttpRequestObjects + Comet Long Polling. (Usually, I'd let GWT or another framework handle of this for me, but I want to learn more about it.)
I wrote the following code:
function longPoll() {
var xhr = createXHR(); // Creates an XmlHttpRequestObject
xhr.open('GET', 'LongPollServlet', true);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
if (xhr.status == 200) {
...
}
if (xhr.status > 0) {
longPoll();
}
}
}
xhr.send(null);
}
...
<body onload="javascript:longPoll()">...
I wrapped the longPoll() call in an if statement that checks for status > 0, because I encountered, that when I leave the page (by browsing somewhere else, or by reloading it), one last unnecessary comet call is sent. [And on Firefox, it even causes severe problems when doing a page reload, for some reason I don't fully understand yet.]
Question: Is that status check the correct way to handle this problem, or is there a better solution?
My current answer - until proven false - is, that the solution is correct.
i like the simplicity of this loop.... i think the server side script has to sleep or atleast loop until it gets new data before its considered long polling though this is just normal polling. i would also add something to check if the reques fails though. wrapping that in a try catch bloch should do the trick

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