Question

i was just wondering if someone could explain this code for me so i can actually learn from it. I am trying to make my app have a scroller that scrolls left to right with loads of pictures (from internet) but the thing is, it must have lazy loading. so i did some tutorials and figured out how to do it but i truly don’t understand it. So i was hoping some kind soul would explain how to lazy load step by step

This is the code i had learned from the tutorials:

-(void)scrollViewDidScroll:(UIScrollView *)myScrollView {
/**
 *  calculate the current page that is shown
 *  you can also use myScrollview.frame.size.height if your image is the exact size of your scrollview
 */
int currentPage = (myScrollView.contentOffset.y / currentImageSize.height);

// display the image and maybe +/-1 for a smoother scrolling
// but be sure to check if the image already exists, you can do this very easily using tags
if ( [myScrollView viewWithTag:(currentPage +1)] ) {
    return;
}
else {
    // view is missing, create it and set its tag to currentPage+1
}

/**
 *  using your paging numbers as tag, you can also clean the UIScrollView
 *  from no longer needed views to get your memory back
 *  remove all image views except -1 and +1 of the currently drawn page
 */
for ( int i = 0; i < currentPages; i++ ) {
    if ( (i < (currentPage-1) || i > (currentPage+1)) && [myScrollView viewWithTag:(i+1)] ) {
        [[myScrollView viewWithTag:(i+1)] removeFromSuperview];
    }
}

}

Answer 1

About Lazy loading on scrollView, I would greatly advised to use UITableView instead. Apple did a great job with performance on this component.

You can have them horizontal (see this EasyTableView code, it works great) and stop the page mode if you want a continuous scroll (pagingEnabled = NO;) so you’ll be able to get the behavior you are looking for.