UIPageControl setCurrentPage - UICollectionView iOS6

Question

I'm new to XCode so I need your help please. I use a UIPageControl to show which cell of my collection View is now visible.

The problem is to get the visible cell:

I think in this Method

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView

I should update the current Page. But how do I get the current Page?

Thanks for your help! :-)

Answer 1

The page can be defined as the ratio between the offset and the size.

- (NSInteger)horizontalPageNumber:(UIScrollView *)scrollView {
    CGPoint contentOffset = scrollView.contentOffset;
    CGSize viewSize = scrollView.bounds.size;

    NSInteger horizontalPage = MAX(0.0, contentOffset.x / viewSize.width);

    // Here's how vertical would work...
    //NSInteger verticalPage = MAX(0.0, contentOffset.y / viewSize.height);

    return horizontalPage;
}

There are a couple ways to trigger this. You can do the work on every scrollViewDidScroll, but that's a bit excessive. A better way is to run it either when dragging is complete and there will be no further deceleration, or when deceleration ends, as follows:

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    self.page.currentPage = [self horizontalPageNumber:scrollView];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (!decelerate) self.page.currentPage = [self horizontalPageNumber:scrollView];
}