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Editorial Team
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Asked: 2026-06-09T21:30:49+00:00

I use UIScrollView to display lots of images. for memory issue, i only load

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I use UIScrollView to display lots of images. for memory issue, i only load three images at a time. when user flick to the next(or previous), i will shift two images and load a new one.

firstly, i use scrollViewDidEndDecelerating methord to determine whether UIScrollView change to next page , previous page or still the current. But when you flick quickly and continuously, scrollViewDidEndDecelerating methord will not receive any message,which means not be called, while scrollViewDidEndDragging:willDecelerate still receive the message. because the dragging is so quick that the previous decelerating be ignored.

So I wonder where can i know whether the view will change and how to judge the changes when i flick quickly? in scrollViewDidEndDragging:willDecelerate methord or some other ways?

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1 Answer

  1. Editorial Team

    I wouldn’t rely on the scrollViewDidEndDecelerating method but will implement the scrollViewDidScroll protocol and update the page when more than 50% of the previous/next page is visible: 

    CGFloat pageWidth = self.scrollView.bounds.size.width;
int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1; 
self.pageControl.currentPage = page;

    EDIT

    Page control combine with scroll view are well explained in this tut

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