UIScrollView notifications

Question

I'm coding an app that works much like Apple's Weather.app: There's a UIPageControl at the bottom and a UIScrollView in the middle of the screen. In my code, I implemented the - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView method to figure out when the user did move to a new page. If they move to a new page, I load the adjacent pages' data, as to make further page-switching faster. (In one of Apple's examples, the - (void)scrollViewDidScroll:(UIScrollView *)sender is used, but that causes my app to shortly hang when loading a new page, so it's not suitable.) That code works very well.

I'm using scrollRectToVisible:: to programmatically scroll inside the scrollview when the user clicks the UIPageControl. The problem is that the scrollRectToVisible: doesn't post a notification to the UIScrollViewDelegate when it's done scrolling - so the code responsible for loading adjacent pages never get's called when using the UIPageControl.

Is there any way to make the UIScrollView notify its delegate when it gets called by the scrollRectToVisible: method? Or will I have to use threads in order to prevent my app from freezing?

Thanks!

-- Ry

Answer 1

How about -scrollViewDidEndScrollingAnimation:?

If it doesn't work, try to listen to the UITextSelectionDidScroll notification. (Of course, it's undocumented.)

Alternatively, an SDK-safe method is measure the time taken for the animation and send a delayed notification at the call site of -scrollRectToVisible:.

Answer 2

You could add this delegate method instead:

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView

The scroll view calls this method at the end of its implementations of the UIScrollView and setContentOffset:animated: and scrollRectToVisible:animated: methods, but only if animations are requested.