UIScrollView: paging horizontally, scrolling vertically?

Question

How can I force a UIScrollView in which paging and scrolling are on to only move vertically or horizontally at a given moment?

My understanding is that

Answer 1

I might be gravedigging here, but I stumbled onto this post today as I was trying to solve the same problem. Here's my solution, seems to be working great.

I want to display a screenful of content, but allow the user to scroll to one of 4 other screenfuls, up down left and right. I have a single UIScrollView with size 320x480 and a contentSize of 960x1440. The content offset starts at 320,480. In scrollViewDidEndDecelerating:, I redraw the 5 views (center views and the 4 around it), and reset the content offset to 320,480.

Here's the meat of my solution, the scrollViewDidScroll: method.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{   
    if (!scrollingVertically && ! scrollingHorizontally)
    {
        int xDiff = abs(scrollView.contentOffset.x - 320);
        int yDiff = abs(scrollView.contentOffset.y - 480);

        if (xDiff > yDiff)
        {
            scrollingHorizontally = YES;
        }
        else if (xDiff < yDiff)
        {
            scrollingVertically = YES;
        }
    }

    if (scrollingHorizontally)
    {
        scrollView.contentOffset = CGPointMake(scrollView.contentOffset.x, 480);
    }
    else if (scrollingVertically)
    {
        scrollView.contentOffset = CGPointMake(320, scrollView.contentOffset.y);
    }
}