Does an iOS app have write access inside its bundle?

Question

I save some run-time generated files inside the .app bundle of my iOS app. In the simulator it works fine, in the device it crashes:

Could create outp

Answer 1

The bundle is read-only. You don't want to mess around with it for two reasons:

• Code Signing: the signature is verified by against the contents of the bundle; if you mess around with the bundle, you break the signature.
• App Updates: updates work by replacing the entire app bundle with a newly downloaded one; any changes you make will get lost.

Where you should save stuff:

• Documents: if you want it to persist and be backed up
• Library/Caches: if you just want to cache downloaded data, like profile pics; will be auto deleted by the system if it is low on room unless you specify with a special do-not-delete flag.
• tmp: temporary files, deleted when your app is not running

For a full explanation check out File System Programming Guide and QA1719.