Only applicationWillResignActive called when iPhone shuts down?

Question

Hallo experts,

I've tested what's happing with my app when the iPhone is switched off while the app is active. For this purpose I logged the callback methods of the app's lifecycle in the xcode debugger console.

The result was: When I press the on/off button of the device for some time applicationWillResignActive is called. The iPhone shows an option to switch off the device on the screen. If I ackknowlege to switch off, the iPhone shuts down. But apperently no further callback methods like applicationDidEnterBackground or applicationWillTerminate are called. As result all data would be lost if I don't save it in applicationWillResignActive. Although the iOS Application Programming Guide says, one should save an app's data in applicationDidEnterBackground and applicationWillTerminate.

What do you think, is one of the two methods still called and is only not printed in the console anymore?

Best regards

Thoria

Interesting observation. It seems possible that it gets called by the console is disconnected by then, but I bet it never even gets called. My hunch is that iOS apps are handled like OSX's sudden termination so the process is killed with no notification. But then again I bet users very rarely turn their device off (if they even know how). – Blisse

But the device also shuts downs if the battery is empty. It's difficult to test an app's behavior in case of an empyty batterie. Because if you connect your iPhone to the development pc to log the callback methods in the console it is charged! But I guess the app behaves similar to manually turning off case. – Thoria

I tested on 3GS running iOS 5.0 ... if switch-off is acknowledged, applicationDidEnterBackground as well as applicationWillTerminate are called! The device logged to console before switching off. – Riyadh

Answer 1

I've made some further tests:

I've saved the called lifecycle methods in a database and turned off the iPhone while may application was running. Actually only applicationWillResignActive is called. But after the shut down my application resides in the state "not running", because launching it initiates calls of application:didFinsihLaunchingWithOptions: and applicationDidBecomeActive. So the application data is lost if I don't save it in applicationWillResignActive.

If the battery is empty while an application is running applicationDidEnterBackground and applicationWillTerminate are called (no call of applicationWillResignActive!).

Thoria

Answer 2

I think that your test is probably correct. The app is no longer active yet it has not gone into the background -- kind of like when I call comes in -- so I think the notifications make sense.

What should you do about it? My suggestion would be nothing. It seems to me that this event happens so infrequently that it's not worth worrying about. If you want to go belt and braces then saving state in ‘applicationWillResignActive‘ should work as long as there's not much to store.

Cabstand

Answer 3

I tested this. This is the order in which the methods are called.

1. applicationWillResignActive - When User long holds the lock button on the device (and a slider is presented asking the user "Slide to power off"

If you slide, the device will call following two methods in your app in the order below

1. applicationDidEnterBackground

2. applciationWillTerminate

The the device will turn off.

I am assuming same happens when the battery drains out.

This was tested on 3Gs running iOS 5.0

Hope this helps.

Riyadh