How to catch cancallation of UIScrollView or others?

Question

Sometimes, interruptions such as phone call occur and disturb a regular behavior of an app in iPhone or iPad.

For example, I created one UIScrollView instance and implemented UIScrollView delegate methods: scrollViewWillBeginDragging and scrollViewDidEndDragging(and scrollViewDidEndDecelerating).

A scrollViewWillBeginDragging method deactivated all custom buttons in my app. Then scrollViewDidEndDragging and scrollViewDidEndDecelerating methods activated these custom buttons. That is, while the user scrolled, all custom buttons became deactivated for a while.

The problem was that while the user started to drag and just held an UIScrollView instance, if I took a screenshot by pressing a home button and a power button, then any of scrollViewDidEndDragging and scrollViewDidEndDecelerating didn't get called. So the app became messed up.

I implemented a UIApplicationWillResignActiveNotification method in my UIViewController, but it didn't get called after taking a screenshot.

How can I catch any kind of interruption that disturbs a regular flow of events?

Sometimes, touchesEnd and touchesCanceled didn't get called too due to an interruption.

Thank you.

Answer 1

I faced the same problem and got rid of it by using performSelector:withObject:afterDelay method of NSObject.

In scrollViewDidScroll:

[NSObject cancelPreviousPerformRequestsWithTarget:yourController];
[yourController deactivateButtons];
[yourController performSelector:@selector(activateButtons) withObject:nil afterDelay:0.5];

You can try this technique and combine it with other that you mentioned.
Hope, that will help. Good luck!