iOS how to detect when app was removed from process

Question

What is the delegate method for detecting when application was closed.

I mean when user tap this button:

I know about method below:

- (void)applicationDidEnterBackground:(UIApplication *)application;

- (void)applicationWillEnterForeground:(UIApplication *)application;

But they work not as I expected in my case. For example I have used my app and I have navigated to some screen. In case when I lock screen and go back to app the app calls applicationWillEnterForeground but I don't need this, because I am still on this view (for example Test Screen View)and I don't need to check any changes. But in case if my app closed I begin to navigate from start app for example Home Screen. So if my app was closed and I am on Home Screen I need to check if in previous time I had some actions (for example if I passed test on Test Screen View) and present this view controller (ONLY IN CASE IF I CLOSED APP NOT JUST LOCKED IT OR ENTER BACKGROUND).

Thanks for help.

Answer 1

You can't detect this. From the iOS App Programming Guide ("App Termination" heading):

Important: The applicationWillTerminate: method is not called if your app is currently suspended.

Even if you develop your app using iOS SDK 4 and later, you must still be prepared for your app to be killed without any notification. The user can kill apps explicitly using the multitasking UI. In addition, if memory becomes constrained, the system might remove apps from memory to make more room. Suspended apps are not notified of termination but if your app is currently running in the background state (and not suspended), the system calls the applicationWillTerminate: method of your app delegate. Your app cannot request additional background execution time from this method.

Answer 2

You can't. When your app is killed in this manner, it is not told anything. The app is killed by the OS with no warning of any kind.

When your app enters the background, you have no way to know if will be started fresh or simply return to the foreground. Therefore you must properly handle things when the app enters the background.

When the app starts again, restore whatever state you need.

Answer 3

On iOS, you cannot check for that. That is: the process is SIGKILL'ed. One way I know that might be able to work relies on the fact that to kill an app, one has to suspend it first by pressing the home button.

Hence, you can gather your actions as the user uses the app, commit it to a saved place when the user suspends the app. If the user resumes, reset the list and start gathering info again. However, if the user suspends the app and you never get a resume, on the next app start, you can read the list and recover from there.

HTH

Answer 4

You can implement the -applicationWillTerminate: method of your UIApplicationDelegate delegate to respond to termination events. However, it's not guaranteed to be called in all cases, so you should not rely on it being called. According to the iOS App Programming Guide:

If your app is running (either in the foreground or background) at termination time, the system calls your app delegate’s applicationWillTerminate: method so that you can perform any required cleanup. You can use this method to save user data or app state information that you would use to restore your app to its current state on a subsequent launch. Your method has approximately 5 seconds to perform any tasks and return. If it does not return in time, the app is killed and removed from memory.

Important: The applicationWillTerminate: method is not called if your app is currently suspended.