iOS中无限循环滚动简单处理实现原理分析

+ (instancetype)loopScrollViewWithFrame:(CGRect)frame;

 //默认滚动到要显示的第一张图片 if (self.imageCollectionView.contentOffset.x == 0) {  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:1 inSection:0];  [self scrollToIndexPath:indexPath animated:NO];  self.currentIndex = 1;}

- (void)setImageList:(NSMutableArray *)imageList { _imageList = imageList; self.loopImageList = [NSMutableArray arrayWithArray:imageList]; if (imageList.count>0) {  [self.loopImageList insertObject:[imageList lastObject] atIndex:0];  [self.loopImageList addObject:[imageList objectAtIndex:0]]; }}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView { CGFloat width = self.bounds.size.width; //在loopImageList中，有n+2个对象，因此index取offset.x/width后的整数 NSInteger index = scrollView.contentOffset.x/width; //这个比值很重要 CGFloat ratio = scrollView.contentOffset.x/width; //从显示的最后一张往后滚，自动跳转到显示的第一张 if (index == self.loopImageList.count-1) {  self.currentIndex = 1;  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.currentIndex inSection:0];  [self scrollToIndexPath:indexPath animated:NO];  return; } //从显示的第一张往前滚，自动跳转到显示的最后一张 //这里判断条件为contentOffset.x和宽的比值，在往前滚快要结束的时候，能达到无缝切换到显示的最后一张的效果 if (ratio <= 0.01) {  self.currentIndex = self.imageList.count;  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.currentIndex inSection:0];  [self scrollToIndexPath:indexPath animated:NO];  return; } if (self.currentIndex != index) {  self.currentIndex = index; } NSLog(@"currentIndex = %ld",self.currentIndex);}