Offline iOS web app: loads my manifest, but doesn't work offline

Question

I\'m writing a web app to be used offline on iOS. I\'ve created a manifest, am serving it up as text/cache-manifest, and it usually works fine, when running in

Answer 1

After days of messing with getting offline web apps to work on an iPhone/iPod Touch using the Webserver's HTTP authentication, I discovered these useful nuggets:

1. Make sure Safari is at the URL root of the web app when tapping "Add to Home Screen". I used jQuery Mobile and was sometimes adding the link with"/#pageId". Caused trouble.

2. Run your Ajax calls in serial. This might only be important if your web app is using HTTP authentication, but my app was firing a whole slew of Ajax calls on page load in parallel and it caused the app to hang on the "apple-touch-startup-image".

3. Ajax calls are "successful" when offline (at least using Prototype.js). Test for an actual piece of data in the Ajax response, not just on the HTTP status. I used this to test for displaying cached (SQL) or live data.

4. In the manifest use "NETWORK:\n*\n". From what I could muster, this is a catch-all statement for anything not explicit in the "CACHE:" section. Use Chrome to make sure your manifest is correct. Look at Chrome's console for errors.

5. Not directly related, but tripped me up for a bit, openDatabase.transaction() calls are ASYNCHRONOUS! Meaning, the line of JS code after transaction (execute(), error(), success()) will execute BEFORE the success() function.

Good luck!

Answer 2

Sometimes an application cache group gets into a bad state in MobileSafari — it downloads every item in the cache and then fires a generic cache error event at the end. An application cache group, as per the spec, is based on the absolute URL of the manifest. I've found that when this error occurs, changing the path to the manifest (eg, cache2.manifest, etc) gives you a fresh cache group and circumvents the problem. I can vouch that all of our web apps work offline in full-screen with 4.2 and 4.3.

Answer 3

I confirm that name 'cache.manifest' solved the offline caching problem in IOS 4.3. Other name simply did not work.

Answer 4

I have found that clearing the Safari cache after enabling Airplane mode to be an effective way of testing whether the app is really functioning offline.

I have sometimes been fooled into thinking that the application cache was working when it wasn't.

Answer 5

I found debugging HTML5 offline apps to be a pain. I found the code from this article helped me figure out what was wrong with my app:

http://jonathanstark.com/blog/2009/09/27/debugging-html-5-offline-application-cache/

Debugging HTML 5 Offline Application Cache by Jonathan Stark

If you are looking to provide offline access to your web app, the Offline Application Cache available in HTML5 is killer. However, it’s a giant PITA to debug, especially if you’re still trying to get your head around it.

If you are struggling with the cache manifest, add the following JavaScript to your main HTML page and view the output in the console using Firebug in Firefox or Debug > Show Error Console in Safari.

If you have any questions, PLMK in the comments.

HTH,
j

var cacheStatusValues = [];
cacheStatusValues[0] = 'uncached';
cacheStatusValues[1] = 'idle';
cacheStatusValues[2] = 'checking';
cacheStatusValues[3] = 'downloading';
cacheStatusValues[4] = 'updateready';
cacheStatusValues[5] = 'obsolete';

var cache = window.applicationCache;
cache.addEventListener('cached', logEvent, false);
cache.addEventListener('checking', logEvent, false);
cache.addEventListener('downloading', logEvent, false);
cache.addEventListener('error', logEvent, false);
cache.addEventListener('noupdate', logEvent, false);
cache.addEventListener('obsolete', logEvent, false);
cache.addEventListener('progress', logEvent, false);
cache.addEventListener('updateready', logEvent, false);

function logEvent(e) {
    var online, status, type, message;
    online = (navigator.onLine) ? 'yes' : 'no';
    status = cacheStatusValues[cache.status];
    type = e.type;
    message = 'online: ' + online;
    message+= ', event: ' + type;
    message+= ', status: ' + status;
    if (type == 'error' && navigator.onLine) {
        message+= ' (prolly a syntax error in manifest)';
    }
    console.log(message);
}

window.applicationCache.addEventListener(
    'updateready',
    function(){
        window.applicationCache.swapCache();
        console.log('swap cache has been called');
    },
    false
);

setInterval(function(){cache.update()}, 10000);

Answer 6

I found this solution that seemed to work for me, since I also ran into this problem during my development. This fix has worked fine for me so far and also for other people that I've asked to test it with, and I'm able to get it running offline (in airplane mode) and off the home screen after caching and whatnot. I've written a post about it on my site:

http://www.offlinewebapp.com/solved-apple-mobile-web-app-capable-manifest-error/

1. Delete your current web app icon on the home screen.
2. Go to settings and clear your Safari browser cache.
3. Double tap your home button to open the multitasking bar. Find the Safari one, hold your finger down on it, and exit it.

Please let me know if this works for you also! Good luck!