How to solve this performSelector:withObject:afterDelay: problem?

Question

I have a view controller, which calls performSelector:withObject:afterDelay. However, if I remove that view controller right after calling this, my app crashes as soon as the system tries to perform the delayed selector on that (deleted) view controller.

Now how can I go about this? I need to get rid of the view controller to save memory, so there's no way to let it hang around.

Any way to cancel a delayed perform selector before it performs?

Answer 1

You can't perform a selector on a deleted object, you either need to have the object around, or do the work with some other smaller object that you can have hanging around.

To cancel there is a cancelPreviousPerformRequestsWithTarget:selector:object: or cancelPreviousPerformRequestsWithTarget: method.

Answer 2

I suggest to use an NSTimer instead. You can simply invalidate the timer to make sure it will never be called after the UIViewController has gone away. A good moment to invalidate the timer is for example in viewWillDisappear:.

This does mean that the timer is owned by the view controller. But that is a good design anyway.