UIScrollView. Any thoughts on implementing “infinite” scroll/zoom?

I’ve just finished implementing the infitine scroll for me.
In my Implementation I have UITableViewCell with a scrollView and Navigationbuttons. The scrollView contains x views all with the same width. views are alined horizontally and paging is enabled.

scrollView.clipsToBounds = YES;
scrollView.scrollEnabled = YES;
scrollView.pagingEnabled = YES;
scrollView.showsHorizontalScrollIndicator = NO;

My codelogic is like the following:

1. In my initialization function I
   • create all the views (for the scrollview) and
   • put them into an array and
   • add them to the scrollView

2. Then I call a function that calculates in a loop the positions for each view (each time you detect a scroll this function will need to be called too). It always takes the first element of the array and sets the frame to (0,0,…,…), the second with (i*width,0,….,….) and so on. The function beeing called looks like this:

   - (void)updateOffsetsOfViews{
       int xpos = 0;
       for (int i=0; i<[views count]; i++) {
           UIImageView *_view = [views objectAtIndex:i];
           CGRect aFrame = _view.frame;
           aFrame.origin.x = xpos;
           aFrame.origin.y = 0.0;
           _view.frame = aFrame;
           xpos += viewWidth;
       }
       float center = 0;
       if(fmod([views count],2) == 1){
           center = viewWidth * ([views count]-1)/2;
       }else {
           center = viewWidth * [views count]/2;
       }
       [scrollView setContentOffset:CGPointMake(center, 0)];
       lastOffset = center;
   }
   

3. Then (still in the initialization process) I add an observer

   [scrollView addObserver:self forKeyPath:@"contentOffset" options:0 context:nil];
   

   so each time something in the scrollView changes I get the (observeValueForKeyPath)-function called, which looks like this:

   - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object  change:(NSDictionary *)change context:(void *)context
   {
       UIImageView *_viewFirst = (UIImageView *)[views objectAtIndex:0];
       if ( fmod([scrollView contentOffset].x,viewWidth)  == 0.0) {
           if ([scrollView contentOffset].x > lastOffset) {
               [views removeObjectAtIndex:0];
               [views addObject:_viewFirst];                
               [self updateOffsetsOfViews];    
           }else if ([scrollView contentOffset].x < lastOffset) {
               UIImageView *_viewLast = (UIImageView *)[views lastObject];
               [views removeLastObject];
               [views insertObject:_viewLast atIndex:0];            
               [self updateOffsetsOfViews];
           }
       }
   }
   

4. And in dealloc or viewDidUnload (depends on how you implement it) don’t forget to remove the observer.

   [scrollView removeObserver:self forKeyPath:@"contentOffset"];   
   

Hope this helps, you might notice some overhead, but in my implementation I also support like scrolling 5 pages (well… unlimited) at once and autoanimated scrolling etc. so you might see something that could be thrown away.