iOS UICollectionViewLayout

UICollectionView调用这四种方法来确定布局信息

- (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect;返回给定矩形中所有视图的数组布局属性实例(返回辅助视图或装饰视图的布局属性，或者根据需要在屏幕上执行布局)

- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;所有布局子类都应该实现该函数:根据需要返回特定索引路径的布局属性实例。

如果布局支持任何补充或装饰视图类型，它还应该为这些类型实现各自的atIndexPath:方法
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;

- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath;

动画相关的函数

/* Returns a transform that scales by `(sx, sy, sz)':
 * t' = [sx 0 0 0; 0 sy 0 0; 0 0 sz 0; 0 0 0 1]. */

CA_EXTERN CATransform3D CATransform3DMakeScale (CGFloat sx, CGFloat sy,
    CGFloat sz)

iOS UICollectionViewLayout