Application getting Killed when kept in Background for Few minutes - ios

Question

When I Open my app & do some stuff (Say navigate to certain
ViewController), then I don't Touch the App for few minutes iPhone gets locked(App Goes in BackGround State).
Now After few
minutes (about 5 minutes) When I Unlock the iPhone My App get Killed.It
is not there in Opened State(Active State). I need to open it explicitly by clicking App Icon.
I am not doing anything in BackGround State
One more thing to add is App is not Crashing

Answer 1

If you checked correctly that your app does not crash, it shows in the multitasking UI and you're not executing code in the background, then I would say that your app is being terminated by the system (due to memory pressure or something else).
Apple's documentation mentions:
Apps must be prepared for termination to happen at any time and should
not wait to save user data or perform other critical tasks.
System-initiated termination is a normal part of an app’s life cycle.
The system usually terminates apps so that it can reclaim memory and
make room for other apps being launched by the user, but the system
may also terminate apps that are misbehaving or not responding to
events in a timely manner.
Suspended apps receive no notification when they are terminated; the
system kills the process and reclaims the corresponding memory. If an
app is currently running in the background and not suspended, the
system calls the applicationWillTerminate: of its app delegate prior
to termination.
So what happened in your scenario is that the app entered the suspended state and after a period of time (those 5 minutes that you mention) the app was terminated by the system.
Take a look at the Background Transition Cycle.
If you want to reduce the possibility that your app will get terminated due to memory pressure, then take a look at What to Do When Your App Enters the Background, specifically:
Free up memory as needed. Release any cached data that you do not need
and do any simple cleanup that might reduce your app’s memory
footprint. Apps with large memory footprints are the first to be
terminated by the system, so release image resources, data caches, and
any other objects that you no longer need. For more information, see
Reduce Your Memory Footprint.

Answer 2

Make sure background modes are on from capabilities options (i have worked on a navigation app and keep app alive in background for more than 8 hours for tracking)
in objective C implement following code
- (void)backgroundCleanDisk {
Class UIApplicationClass = NSClassFromString(#"UIApplication");
if(!UIApplicationClass || ![UIApplicationClass respondsToSelector:#selector(sharedApplication)]) {
return;
}
UIApplication *application = [UIApplication performSelector:#selector(sharedApplication)];
__block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler:^{
// Clean up any unfinished task business by marking where you
// stopped or ending the task outright.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
// Start the long-running task and return immediately.
[self cleanDiskWithCompletionBlock:^{
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
}