Difference in scheduling NSTimer in main thread and background thread?

Question

When I call scheduledTimerWithTimeInterval:target:selector:userInfo:repeats: on the main thread and set time interval to 5 seconds code below timer gets execute

Answer 1

NSTimer requires an active run loop, when initialized in Main Thread it automatically uses the main run loop. If you need to make a background timer you need attach it to the thread’s run loop and invoke run() to make it active.

1. NSTimer needs one live NSRunLoop to execute it’s events. In main thread, the NSRunLoop is always live and will never stop until the app is terminated, but in other threads, you must invoke run() to active the NSRunLoop.

2. NSTimer must invoke invalidate() to release the current timer, otherwise, the timer will retain a strong reference of the current instance of target, and it will remain in memory until invalidate() invoked or app terminated;

3. NSTimer must created and invalidated in the same thread, and a lot of times, we may forget that.

Take a look at this example , it may be helpful >> http://www.acttos.org/2016/08/NSTimer-and-GCD-Timer-in-iOS/ and the documentation : https://developer.apple.com/documentation/foundation/nstimer