iOS UICollectionView 在滚动时停在某个item位置上

方法一：实现UIScrollView的代理，然后实现下面这个方法

#pragma mark - UIScrollViewDelegate
//预计出大概位置，经过精确定位获得准备位置
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset{
CGPoint targetOffset = [self nearestTargetOffsetForOffset:*targetContentOffset];
targetContentOffset->x = targetOffset.x;
targetContentOffset->y = targetOffset.y;
}
//计算落在哪个item上
- (CGPoint)nearestTargetOffsetForOffset:(CGPoint)offset
{
CGFloat pageSize = itemSpacing + itemWidth;
//四舍五入
NSInteger page = roundf(offset.x / pageSize);
CGFloat targetX = pageSize * page;
return CGPointMake(targetX, offset.y);
}

方法二：重写UICollectionViewFlowLayout

参考文献：http://tech.glowing.com/cn/practice-in-uiscrollview/
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作者：C_calary
来源：CSDN
原文：https://blog.csdn.net/C_calary/article/details/78891724
版权声明：本文为博主原创文章，转载请附上博文链接！

UICollectionView横向移动时，且UICollectionView.page = yes只显示一个Cell 移动时姑且计算划至第几个cell

#pragma mark - collectionView

- (UICollectionView *)collectionView

{

if (!_collectionView) {

UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];

layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;

_collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, screenHeight - kTopHeight - Height_BottomView) collectionViewLayout:layout];

_collectionView.dataSource = self;

_collectionView.delegate = self;

_collectionView.pagingEnabled = YES;

//        _collectionView.scrollEnabled = !GetAnswernextque; // 如果只能滑动至下一题取消滚动效果

[_collectionView registerClass:[AnswerCollectionViewCell class] forCellWithReuseIdentifier:@"AnswerCollectionViewCell"];

_collectionView.backgroundColor = [UIColor whiteColor];

_collectionView.showsVerticalScrollIndicator = NO;

_collectionView.showsHorizontalScrollIndicator = NO;

[self.view addSubview:_collectionView];

}

return _collectionView;

}

#pragma mark - UICollectionViewDelegate

//预计出大概位置，经过精确定位获得准备位置

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset{

CGPoint targetOffset = [self nearestTargetOffsetForOffset:*targetContentOffset];

targetContentOffset->x = targetOffset.x;

targetContentOffset->y = targetOffset.y;

//    self.currentIndexPath

NSInteger index = targetOffset.x/screenWidth;

DLog(@"---------%ld",index);

self.currentIndexPath = [NSIndexPath indexPathForItem:index inSection:0];

self.lbPageIndex.text = [NSString stringWithFormat:@"%li/%li",self.currentIndexPath.item,self.dataSource.count];

}

//计算落在哪个item上

- (CGPoint)nearestTargetOffsetForOffset:(CGPoint)offset

{

CGFloat pageSize = screenWidth;

//四舍五入

NSInteger page = roundf(offset.x / pageSize);

CGFloat targetX = pageSize * page;

return CGPointMake(targetX, offset.y);

}

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

CGPoint offsetPoint = scrollView.contentOffset;

self.currentIndexPath = [NSIndexPath indexPathForItem:offsetPoint.x/(screenWidth) inSection:0];

self.lbPageIndex.text = [NSString stringWithFormat:@"%li/%li",self.currentIndexPath.item,self.dataSource.count];

}

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

CGPoint offsetPoint = scrollView.contentOffset;

self.currentIndexPath = [NSIndexPath indexPathForItem:offsetPoint.x/(screenWidth) inSection:0];

self.lbPageIndex.text = [NSString stringWithFormat:@"%li/%li",self.currentIndexPath.item,self.dataSource.count];

}

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

CGPoint offsetPoint = scrollView.contentOffset;

self.currentIndexPath = [NSIndexPath indexPathForItem:offsetPoint.x/(screenWidth) inSection:0];

self.lbPageIndex.text = [NSString stringWithFormat:@"%li/%li",self.currentIndexPath.item,self.dataSource.count];

}

#pragma mark - FlipPageDelegate

- (void)flipToNextPage{

CGPoint offsetPoint = self.collectionView.contentOffset;

NSInteger pageIndex = offsetPoint.x / screenWidth;

if (pageIndex < self.dataSource.count - 1) {

pageIndex++;

NSIndexPath *curIndexPath = [NSIndexPath indexPathForItem:pageIndex inSection:0];

self.currentIndexPath = curIndexPath;

        self.lbPageIndex.text = [NSString stringWithFormat:@"%li/%li",pageIndex,self.dataSource.count];

NSIndexPath *indexPath = [NSIndexPath indexPathForItem:pageIndex inSection:0];

[self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];

}else{

[ToolUtils showSuccess:@"已经是最后一页"];

}

}