IOS flushes standalone cached HTML5 data

Question

We developed a standalone HTML5 web application using the .manifest caching mechanism. Everything works as expected.

Now, some of our customers complain that after long-term use in offline mode, the cached data suddenly disappeared. It turns out - this is my guess - iOS stores cached files in the / CACHES / directory, which, starting with iOS 5.0, can be cleared if the device leaves space. This can happen at any time, even without warning the user. Consequently, standalone webapp is no longer working properly. The user must connect the device to the Internet and update the application.

For native applications, this problem is solved by storing files in the / DOCUMENTS / dir directory using the Do Not Back Up flag, which prevents files from being cleaned up (since they are not in the / CACHES / dir directory and are not supported in iCloud or iTunes.

See this link for more details: http://www.marco.org/2011/10/13/ios5-caches-cleaning , however this doesn't say anything about HTML5 caching ...

This explains it again, however no solution: http://www.moneytoolkit.com/2012/04/apple-ios-html5-localstorage-is-broken/

Has anyone experienced the same thing? Is there a solution to this? The goal is to install the web application once and then launch it without connecting forever ...

Cheers pawi

Answer 1

There is no way around this in Safari. A cache is never considered permanent.

If you have a UIWebView inside your own application, you can set WebKitStoreWebDataForBackup to YES in your default settings. (iOS 6+ only)