Nested UIScrollViews and event routing

Question

I have 2 scroll views, both of which are supposed to scroll vertically. The outer scroll view (red) contains a search bar and the inner scroll view (blue). The inner scroll view is supposed to scroll infinitely (it contains images/items and has an endless scrolling implementation).

The way I want this controller to work is as follows:

When I scroll down, the outer scroll view should scroll first and the search bar should disappear (scroll out of the content area). Only after that the inner scroll view should start scrolling. When scrolling back up, the inner scroll view should scroll all the way to its top. Only then the outer scroll view should take the scroll events and finally scroll up to make the search bar visible again.

If I just nest them in IB without any modifications the inner scroll view catches all the scroll events and it works the other way around.

Please bear in mind that I'm using the inner scroll view as a simplifying metaphor here. In my app I actually have a control here, which has a scroll view with nested table views (scroll view lets me page horizontally, table views let me scroll vertically).

Answer 1

If you are able to, set a common UIScrollViewDelegate on the 2 scroll views, and implement the following:

- (void) scrollViewDidScroll: (UIScrollView*) scrollView
{
  if (scrollView == self.mainScrollView)
  {
    /* Handle instances when the main scroll view is already at the bottom */
    if (   scrollView.contentOffset.y
        == scrollView.contentSize.height - scrollView.bounds.size.height)
    {
      /* Stop scrolling the main scroll view and start scrolling the
       * inner scroll view
       */
      self.innerScrollView.scrollEnabled = YES;
      self.mainScrollView.scrollEnabled = NO;
    }
    else
    {
      /* Start scrolling the main scroll view and stop scrolling the
       * inner scroll view
       */
      self.innerScrollView.scrollEnabled = NO;
      self.mainScrollView.scrollEnabled = YES;
    }
  }
  else if (scrollView == self.innerScrollView)
  {
    /* Handle instances when the inner scroll view is already at the top */
    if (self.innerScrollView.contentOffset.y == 0)
    {
      /* Stop scrolling the inner scroll view and start scrolling the
       * main scroll view
       */
      self.innerScrollView.scrollEnabled = NO;
      self.mainScrollView.scrollEnabled = YES;
    }
    else
    {
      /* Start scrolling the inner scroll view and stop scrolling the
       * main scroll view
       */
      self.innerScrollView.scrollEnabled = YES;
      self.mainScrollView.scrollEnabled = NO;
    }
  }
}

Please note that I haven't tested this, but the logic could be somewhat like this (either you set scrolling enabled or you disable user interaction, or something). Most probably this will not be enough of a solution as you would like, but I'm sure a common UIScrollViewDelegate is the solution to your problem.