CODEWITHSUNDEEP
iosobjective-ciphone
Paragon
Paragon

Reputation: 1012

when iOS removes an app from memory

This question might have been asked before but i couldn't find an answer. If i open an app and press home button it goes in background and if i open it again it calls app delegate methods such as "applicationWillEnterForeground". How long it will take me to be in background so app calls didFinishLaunchingWithOptions and starts the fresh app?

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

Thanks

Upvotes: 2

Views: 2101

Answers (2)

Bartek Chlebek
Bartek Chlebek

Reputation: 1663

There are many factors that are taken under consideration to remove your app from the memory (kill the process).

The most simple one is rebooting the device. All apps are off after a reboot. Apps with Voip however are launched automatically into the background after a reboot.

The second and most common one is memory pressure. If your app is in the background and system runs out of RAM, it kills the suspended apps starting from the one that consumes the most RAM and keeps killing them until it reclaims enough memory.

Another, quite common one is something known as the watchdog. There are specific scenarios when your app's main thread has a limited time to finish the task. For example, when you app returns from the background or when the user presses the home button, you have about 10s to free the main thread. (Keep in mind there are situations such as background tasks, music playback and other, that grant your app more execution time in the background).
But, a typical app will be killed if the runloop does not return in about 10.

Another case worth mentioning is if your app uses very little RAM. It was mentioned in one of WWDC sessions, that if your application consumes no more than 16MB of RAM, it will be dumped to flash storage, and restored back to the memory on reopening, rather than being killed. So in this case your app may never be killed (I'm not sure about the reboot, but I assume the dumped image is ignored after a reboot and a normal launch process happens).

Next one is the user's explicit action, that is entering the multitasking UI and swiping the app upwards, which will kill the application.

I think that sums up the most common scenarios.

And of course you might also want to have a look at the docs: https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/TheAppLifeCycle/TheAppLifeCycle.html#//apple_ref/doc/uid/TP40007072-CH2-SW1

Upvotes: 4

Phil Viso
Phil Viso

Reputation: 643

How much RAM does the device have? Have much RAM was your app using? Are you following best practices when your app receives didReceiveMemoryWarning:? Are you opening other apps before going back to yours? This is such a "it depends" question.

What's the larger question here? Why do you want to know when your app will get purged from memory?

Upvotes: 0

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