How to implement UIScrollView with 1000+ subviews?

Question

I am struggling with writing portion of an app which should behave like the native iphone photo app. Looked at iphone sdk app development book from Orielly which gave an exa

Answer 1

Many thanks to Adrian for his very simple and powerfull code sample. There was just one issue with this code : when the user made a "double scroll" (I.E. when he did not wait for the animation to stop and rescroll the scrollview again and again).

In this case, the refresh for the position of the 3 subviews is effective only when the "scrollViewDidEndDecelerating" method is invoked, and the result is a delay before the apparition of the subviews on the screen.

This can be easily avoided by adding few lines of code :

in the interface, just add this :

int refPage, currentPage;

in the implementation, initialize refPage and currentPage in the "viewDidLoad" method like this :

refpage = 0; 
curentPage = 0;

in the implementation, just add the "scrollViewDidScroll" method, like this :

- (void)scrollViewDidScroll:(UIScrollView *)sender{
    int currentPosition = floor(_scrollView.contentOffset.x);
    currentPage = MAX(0,floor(currentPosition / 340)); 
//340 is the width of the scrollview...
    if(currentPage != refPage)  { 
        refPage = currentPage;
        [self replaceHiddenLabels];
        }
    }

et voilà !

Now, the subviews are correctly replaced in the correct positions, even if the user never stop the animation and if the "scrollViewDidEndDecelerating" method is never invoked !