重写UICollectionView的FlowLayout布局
- (instancetype)init{ if (self = [super init]) { self.itemSize = CGSizeMake(kScreenWidth / 2, kScreenHeight / 2 - 49 - 30); self.minimumLineSpacing = 2; self.minimumInteritemSpacing = 2; self.sectionInset = UIEdgeInsetsMake(2, 2, 2, 2); } return self;}/** * collectionView的显示范围发生改变的时候，调用下面这个方法是否重新刷新 * * @param newBounds * * @return 是否重新刷新 */- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{ return YES;}/** * 布局的初始化操作 */- (void)prepareLayout{ [super prepareLayout]; // 设置为水平滚动 self.scrollDirection = UICollectionViewScrollDirectionHorizontal; // 设置内边距 CGFloat insetGap = (self.collectionView.frame.size.width - self.itemSize.width) * 0.5; self.sectionInset = UIEdgeInsetsMake(0, insetGap, 0, insetGap);}/** * 设置cell的显示大小 * * @param rect 范围 * * @return 返回所有元素的布局 */- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{ // 获取计算好的布局属性 NSArray *arr = [[NSArray alloc]initWithArray:[super layoutAttributesForElementsInRect:rect] copyItems:YES]; for (int i = 0; i < arr.count; i ++) { UICollectionViewLayoutAttributes *att = arr[i]; //算比例 //拿到每个item的位置 算出itemCenterX 和collectionCenterX 的一个距离 CGFloat distance = ABS(att.center.x - self.collectionView.frame.size.width * 0.5 - self.collectionView.contentOffset.x); CGFloat scale = 0.5; CGFloat w = (self.collectionView.frame.size.width + self.itemSize.width) * 0.5; if (distance >= w) { scale = 0.5; }else{ scale = scale + (1- distance / w ) * 0.5; } att.transform = CGAffineTransformMakeScale(scale, scale); } return arr;}//滑动完成后，会来到此方法 - 线性滑动//proposedContentOffset 最后停止的 contentOffset- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity{ //proposedContentOffset 滑动之后最后停的位置 CGRect rect; rect.origin = proposedContentOffset; rect.size = self.collectionView.frame.size; //获取停止时，显示的cell的frame //NSArray *tempArray = [super layoutAttributesForElementsInRect:rect]; NSArray *tempArray = [[NSArray alloc]initWithArray:[super layoutAttributesForElementsInRect:rect] copyItems:YES]; CGFloat gap = 1000; CGFloat a = 0; for (int i = 0; i < tempArray.count; i++) { //判断和中心的距离，得到最小的那个 if (gap > ABS([tempArray[i] center].x - proposedContentOffset.x - self.collectionView.frame.size.width * 0.5)) { gap = ABS([tempArray[i] center].x - proposedContentOffset.x - self.collectionView.frame.size.width * 0.5); a = [tempArray[i] center].x - proposedContentOffset.x - self.collectionView.frame.size.width * 0.5; } } CGPoint point =CGPointMake(proposedContentOffset.x + a , proposedContentOffset.y); return point;}复制代码