iPhone applicationDidEnterBackground: method to save user data and any state information

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+2 Q:

iPhone applicationDidEnterBackground: method to save user data and any state information

Hi Guys,

What is the best approach to save any application state information or user data information before application goes to background?

Say for example I have one application level variable called "Authorised". Where should I save this information so I can get it back if it is purged by memory management.

Regards,

Atif

+2 A:

Well that depends a bit how big and complex the data is you want to save. If it is just a small amount of data representing the state, I would have a look at NSUserDefaults.

Have a look at this question as well:How to show the same view when the app is reopened

GorillaPatch 2010-06-28 11:19:32

Is there any case in which my application level variable "Authorised" (not data) deallocated or released?

Leo 2010-06-28 11:26:20

Yes of course. When your app goes into background its state is maintained. But if you are using other programs then it could be that your app will be terminated. This would mean that your variable is gone.So just save your variable in the delegate method on UIApplication- (void)applicationWillResignActive:(UIApplication *)applicationThen restore its value when your application delegate's method- (void)applicationDidBecomeActive:(UIApplication *)application

GorillaPatch 2010-06-28 16:08:14

There is a nice overview of the possible application's state here: http://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/CoreApplication/CoreApplication.html#//apple_ref/doc/uid/TP40007072-CH3-SW10

GorillaPatch 2010-06-28 16:08:40

Hi,My app goes into background and foreground fine unless I open a few more applications.What's happening If I open my app after opening some other applications like games is that my application gives me memory warning lavel 2 and then crash. And sometimes it does not give any warning and just freez the screen for a bit and then crash.Any idea what's going on?

Leo 2010-06-29 07:50:43

Not really. What is important is that you really save your state when your AppDelegate gets the - (void)applicationWillResignActive: message. You do not have the time to save anything in applicationWillTerminate, which is another delegate message.For me it sounds that you execute code during startup which you should not. This may cause memory leaks and you are dead. It could be that you initializing something twice without releasing the old version, but I am just guessing here. Try using Instruments to analyze your memory footprint. Make sure you do not leak any memory.

GorillaPatch 2010-06-29 09:08:51

ansaurus

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iPhone applicationDidEnterBackground: method to save user data and any state information

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