iosiphonepaginationuiscrollviewuiimageview

ios uiscrollview with pagingenabled between uiimageviews how to detect which one is on the screen/visible

So I have a UIScrollview that scrolls horizontally with paging through a bunch of different UIImageViews containing user avatars. But, I want to only load the avatars from their URL IFF they are actually showing on the screen (4 are showing at a time, but I can scroll through like 30 or more or less). Is there a way of detecting which UIImageView/ which page it is on? Or does anyone have any general recommendations or ideas for how I should go about this problem? Thank you in advance.

Solution

  • -(void)scrollViewDidScroll:(UIScrollView *)scrollView{ 

    -(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
        CPoint offset = scrollView.contentOffset;
        int index = offset.x / pageWidth;
        switch (index) {
            case 0:
                //first ImageView
                break;
            case 1:
                //second ImageView
                break;
            default:
                break;
        }
    }

    Or If you tag your imageViews (starting at 1) you can retrieve them via:

    -(void)scrollViewDidScroll:(UIScrollView *)scrollView{ 

    -(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
    CPoint offset = scrollView.contentOffset;
    int index = offset.x / pageWidth;
    UIImageView *visibileImageView = (id)[scrollView viewWithTag:index+1];
}

    You can use scrollViewDidScroll to detect the position at any point if you use the modulus:

    int index = (offset.x - offset.x % pageWidth)/pageWidth;