//通過一個布局策略初識化CollectionView
- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout;

//獲取和設置collection的layout
@property (nonatomic, strong) UICollectionViewLayout *collectionViewLayout;

//數據源和代理
@property (nonatomic, weak, nullable) id <UICollectionViewDelegate> delegate;
@property (nonatomic, weak, nullable) id <UICollectionViewDataSource> dataSource;

//從一個class或者xib文件進行cell(item)的注冊
- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;

//下面兩個方法與上面相似，這里注冊的是頭視圖或者尾視圖的類
//其中第二個參數是設置 頭視圖或者尾視圖 系統為我們定義好了這兩個字符串
//UIKIT_EXTERN NSString *const UICollectionElementKindSectionHeader NS_AVAILABLE_IOS(6_0);
//UIKIT_EXTERN NSString *const UICollectionElementKindSectionFooter NS_AVAILABLE_IOS(6_0);
- (void)registerClass:(nullable Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forSupplementaryViewOfKind:(NSString *)kind withReuseIdentifier:(NSString *)identifier;

//這兩個方法是從復用池中取出cell或者頭尾視圖
- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;

//設置是否允許選中 默認yes
@property (nonatomic) BOOL allowsSelection;

//設置是否允許多選 默認no
@property (nonatomic) BOOL allowsMultipleSelection;

//獲取所有選中的item的位置信息
- (nullable NSArray<NSIndexPath *> *)indexPathsForSelectedItems; 

//設置選中某一item，并使視圖滑動到相應位置，scrollPosition是滑動位置的相關參數，如下：
/*
typedef NS_OPTIONS(NSUInteger, UICollectionViewScrollPosition) {
    //無
    UICollectionViewScrollPositionNone                 = 0,
    //垂直布局時使用的 對應上中下
    UICollectionViewScrollPositionTop                  = 1 << 0,
    UICollectionViewScrollPositionCenteredVertically   = 1 << 1,
    UICollectionViewScrollPositionBottom               = 1 << 2,
    //水平布局時使用的  對應左中右
    UICollectionViewScrollPositionLeft                 = 1 << 3,
    UICollectionViewScrollPositionCenteredHorizontally = 1 << 4,
    UICollectionViewScrollPositionRight                = 1 << 5
};
*/
- (void)selectItemAtIndexPath:(nullable NSIndexPath *)indexPath animated:(BOOL)animated scrollPosition:(UICollectionViewScrollPosition)scrollPosition;

//將某一item取消選中
- (void)deselectItemAtIndexPath:(NSIndexPath *)indexPath animated:(BOOL)animated;

//重新加載數據
- (void)reloadData;

//下面這兩個方法，可以重新設置collection的布局，后面的方法多了一個布局完成后的回調，iOS7后可以用
//使用這兩個方法可以產生非常炫酷的動畫效果
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated;
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);

//下面這些方法更加強大，我們可以對布局更改后的動畫進行設置
//這個方法傳入一個布局策略layout，系統會開始進行布局渲染，返回一個UICollectionViewTransitionLayout對象
//這個UICollectionViewTransitionLayout對象管理動畫的相關屬性，我們可以進行設置
- (UICollectionViewTransitionLayout *)startInteractiveTransitionToCollectionViewLayout:(UICollectionViewLayout *)layout completion:(nullable UICollectionViewLayoutInteractiveTransitionCompletion)completion NS_AVAILABLE_IOS(7_0);
//準備好動畫設置后，我們需要調用下面的方法進行布局動畫的展示，之后會調用上面方法的block回調
- (void)finishInteractiveTransition NS_AVAILABLE_IOS(7_0);
//調用這個方法取消上面的布局動畫設置，之后也會進行上面方法的block回調
- (void)cancelInteractiveTransition NS_AVAILABLE_IOS(7_0);

//獲取分區數
- (NSInteger)numberOfSections;

//獲取某一分區的item數
- (NSInteger)numberOfItemsInSection:(NSInteger)section;

//下面兩個方法獲取item或者頭尾視圖的layout屬性，這個UICollectionViewLayoutAttributes對象
//存放著布局的相關數據，可以用來做完全自定義布局
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;

//獲取某一點所在的indexpath位置
- (nullable NSIndexPath *)indexPathForItemAtPoint:(CGPoint)point;

//獲取某個cell所在的indexPath
- (nullable NSIndexPath *)indexPathForCell:(UICollectionViewCell *)cell;

//根據indexPath獲取cell
- (nullable UICollectionViewCell *)cellForItemAtIndexPath:(NSIndexPath *)indexPath;

//獲取所有可見cell的數組
- (NSArray<__kindof UICollectionViewCell *> *)visibleCells;

//獲取所有可見cell的位置數組
- (NSArray<NSIndexPath *> *)indexPathsForVisibleItems;

//下面三個方法是iOS9中新添加的方法，用于獲取頭尾視圖
- (UICollectionReusableView *)supplementaryViewForElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
- (NSArray<UICollectionReusableView *> *)visibleSupplementaryViewsOfKind:(NSString *)elementKind NS_AVAILABLE_IOS(9_0);
- (NSArray<NSIndexPath *> *)indexPathsForVisibleSupplementaryElementsOfKind:(NSString *)elementKind NS_AVAILABLE_IOS(9_0);

//使視圖滑動到某一位置，可以帶動畫效果
- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated;

//下面這些方法用于動態添加，刪除，移動某些分區獲取items
- (void)insertSections:(NSIndexSet *)sections;
- (void)deleteSections:(NSIndexSet *)sections;
- (void)reloadSections:(NSIndexSet *)sections;
- (void)moveSection:(NSInteger)section toSection:(NSInteger)newSection;

- (void)insertItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths;
- (void)deleteItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths;
- (void)reloadItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths;
- (void)moveItemAtIndexPath:(NSIndexPath *)indexPath toIndexPath:(NSIndexPath *)newIndexPath;