dumping data to file when app quits

Question

What do you all recommend as the best location in an iphone project to dump data collected from the user to a local file? Would you say that applicationWillTerminate is a good option?

Thanks!

Answer 1

A better option on iOS 4.x is applicationDidEnterBackground:

Indeed, according to Apple docs, an application in the background can be terminated at any time due to low memory conditions. Therefore, the suggestion is making persistent any state information at the moment the app enters background.

An excerpt from the UIApplicationDelegate protocol :

You should use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. You should also disable updates to your application's user interface and avoid using some types of shared system resources (such as the user's contacts database). It is also imperative that you avoid using OpenGL ES in the background.

Your implementation of this method has approximately five seconds to perform any tasks and return. If you need additional time...

Answer 2

Also from Apple Docs for applicationWillTerminate:

For applications that do not support background execution or are linked against iOS 3.x or earlier, this method is always called when the user quits the application. For applications that support background execution, this method is generally not called when the user quits the application because the application simply moves to the background in that case. However, this method may be called in situations where the application is running in the background (not suspended) and the system needs to terminate it for some reason.

Therefore if you specifically request to not support backgrounding for your app or you link against iOS 3.x you should consider persisting in both places (applicationWillTerminate and applicationWillEnterBackground) to catch situations as well.