UICollectionView基础API笔记

//直接初始化方法，需要提供一个Layout
- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout NS_DESIGNATED_INITIALIZER;
//从nib文件直接初始化
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;
//当前Layout
@property (nonatomic, strong) UICollectionViewLayout *collectionViewLayout;
//用户交互Delegate
@property (nonatomic, weak, nullable) id <UICollectionViewDelegate> delegate;
//UI的数据源DataSource
@property (nonatomic, weak, nullable) id <UICollectionViewDataSource> dataSource;

//iOS10新增加的Pre-Fetching预加载协议
@property (nonatomic, weak, nullable) id<UICollectionViewDataSourcePrefetching> prefetchDataSource NS_AVAILABLE_IOS(10_0);
//是否允许预加载
@property (nonatomic, getter=isPrefetchingEnabled) BOOL prefetchingEnabled NS_AVAILABLE_IOS(10_0);
//背景图片，自动根据collectionView的大小调整
@property (nonatomic, strong, nullable) UIView *backgroundView; 

//注册UICollectionViewCell，或其子类，并且提供一个复用标识符，在runtime的时候会初始化这个对象
- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;
//通过nib文件注册复用cell
- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;
//通过Class注册补充视图，并且指定补充视图的种类
- (void)registerClass:(nullable Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier;
//通过nib文件注册补充视图
- (void)registerNib:(nullable UINib *)nib forSupplementaryViewOfKind:(NSString *)kind withReuseIdentifier:(NSString *)identifier;

//从复用队列通过指定Identifier获取复用cell
- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
//从复用队列通过指定Identifier获取复用ReusableView 
- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;

//是否允许items选中，默认YES
@property (nonatomic) BOOL allowsSelection; // default is YES
//是否允许items多选，默认NO
@property (nonatomic) BOOL allowsMultipleSelection; // default is NO

//返回选中的index paths，返回nil或者NSArray
#if UIKIT_DEFINE_AS_PROPERTIES
@property (nonatomic, readonly, nullable) NSArray<NSIndexPath *> *indexPathsForSelectedItems; 
#else
- (nullable NSArray<NSIndexPath *> *)indexPathsForSelectedItems; 
#endif

//选中和解选indexPath对应item，可指定动画和UICollectionViewScrollPosition
- (void)selectItemAtIndexPath:(nullable NSIndexPath *)indexPath animated:(BOOL)animated scrollPosition:(UICollectionViewScrollPosition)scrollPosition;
- (void)deselectItemAtIndexPath:(NSIndexPath *)indexPath animated:(BOOL)animated;

//刷新数据
- (void)reloadData; 

//切换当前collectionView的layout
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated; 
//切换当前collectionView的layout，配置完成之后的block(iOS7之后可用)
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);
//改变当前collectionView的layout，使用interactive transition effect.
- (UICollectionViewTransitionLayout *)startInteractiveTransitionToCollectionViewLayout:(UICollectionViewLayout *)layout completion:(nullable UICollectionViewLayoutInteractiveTransitionCompletion)completion NS_AVAILABLE_IOS(7_0);
//layout切换过渡完成
- (void)finishInteractiveTransition NS_AVAILABLE_IOS(7_0);
//取消过渡切换layout
- (void)cancelInteractiveTransition NS_AVAILABLE_IOS(7_0);

//下面是UICollectionView的状态信息

//返回section的数量
#if UIKIT_DEFINE_AS_PROPERTIES
@property (nonatomic, readonly) NSInteger numberOfSections;
#else
- (NSInteger)numberOfSections;
#endif
//返回对应section中item的数量
- (NSInteger)numberOfItemsInSection:(NSInteger)section;
//返回对应indexPath的item的LayoutAttributes
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
//返回对应indexPath的ReuseView的LayoutAttributes
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
//返回对应point的indexPath
- (nullable NSIndexPath *)indexPathForItemAtPoint:(CGPoint)point;
//返回对应cell的indexPath
- (nullable NSIndexPath *)indexPathForCell:(UICollectionViewCell *)cell;
//返回对应indexPath的cell
- (nullable UICollectionViewCell *)cellForItemAtIndexPath:(NSIndexPath *)indexPath;

//返回collectionView当前可见的item数组和可见item的indexPath数组
#if UIKIT_DEFINE_AS_PROPERTIES
@property (nonatomic, readonly) NSArray<__kindof UICollectionViewCell *> *visibleCells;
@property (nonatomic, readonly) NSArray<NSIndexPath *> *indexPathsForVisibleItems;
#else
- (NSArray<__kindof UICollectionViewCell *> *)visibleCells;
- (NSArray<NSIndexPath *> *)indexPathsForVisibleItems;
#endif

//返回对应indexPath的ReuseView(iOS9之后可用)
- (nullable UICollectionReusableView *)supplementaryViewForElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
//返回collectionView当前可见的ReuseView数组