#import <UIKit/UIScrollView.h>
#import <UIKit/UIKitDefines.h>
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

typedef NS_OPTIONS(NSUInteger, UICollectionViewScrollPosition) {
    UICollectionViewScrollPositionNone                 = 0,
    
    // The vertical positions are mutually exclusive to each other, but are bitwise or-able with the horizontal scroll positions.
    // Combining positions from the same grouping (horizontal or vertical) will result in an NSInvalidArgumentException.
    UICollectionViewScrollPositionTop                  = 1 << 0,
    UICollectionViewScrollPositionCenteredVertically   = 1 << 1,
    UICollectionViewScrollPositionBottom               = 1 << 2,
    
    // Likewise, the horizontal positions are mutually exclusive to each other.
    UICollectionViewScrollPositionLeft                 = 1 << 3,
    UICollectionViewScrollPositionCenteredHorizontally = 1 << 4,
    UICollectionViewScrollPositionRight                = 1 << 5
};

@class UICollectionView;
@class UICollectionViewCell;
@class UICollectionViewLayout;
@class UICollectionViewTransitionLayout;
@class UICollectionViewLayoutAttributes;
@class UITouch;
@class UINib;
@class UICollectionReusableView;

// layout transition block signature
typedef void (^UICollectionViewLayoutInteractiveTransitionCompletion)(BOOL completed, BOOL finished);

NS_CLASS_AVAILABLE_IOS(9_0) @interface UICollectionViewFocusUpdateContext : UIFocusUpdateContext

@property (nonatomic, strong, readonly, nullable) NSIndexPath *previouslyFocusedIndexPath;
@property (nonatomic, strong, readonly, nullable) NSIndexPath *nextFocusedIndexPath;

@end

@protocol UICollectionViewDataSource <NSObject>
@required

//返回单元格（items）个数（必须实现）
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section;

// 必须从复用中取得-dequeueReusableCellWithReuseIdentifier:forIndexPath:
//根据indexPath属性，返回该单元格的具体样式和显示内容（必须实现）
- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;

@optional

//返回组数据个数，默认为1
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView;

// 必须也从复用的队列中取得-dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
//设置头尾视图，同样也要先注册
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;

//设置是否可以移动单元格
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);

//移动单元格的具体设置
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath NS_AVAILABLE_IOS(9_0);

@end

@protocol UICollectionViewDataSourcePrefetching <NSObject>
@required
// indexPaths are ordered ascending by geometric distance from the collection view
- (void)collectionView:(UICollectionView *)collectionView prefetchItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths NS_AVAILABLE_IOS(10_0);

@optional
// indexPaths that previously were considered as candidates for pre-fetching, but were not actually used; may be a subset of the previous call to -collectionView:prefetchItemsAtIndexPaths:
- (void)collectionView:(UICollectionView *)collectionView cancelPrefetchingForItemsAtIndexPaths:(NSArray<NSIndexPath *> *)indexPaths  NS_AVAILABLE_IOS(10_0);

@end


@protocol UICollectionViewDelegate <UIScrollViewDelegate>
@optional

//下面是整个点击高亮显示过程中的调用顺序
//
// 当触摸开始调用
// 1. -collectionView:shouldHighlightItemAtIndexPath:
// 2. -collectionView:didHighlightItemAtIndexPath:
//
//当手指离开调用
// 3. -collectionView:shouldSelectItemAtIndexPath: or -collectionView:shouldDeselectItemAtIndexPath:
// 4. -collectionView:didSelectItemAtIndexPath: or -collectionView:didDeselectItemAtIndexPath:
// 5. -collectionView:didUnhighlightItemAtIndexPath:

//设置item是否能够高亮
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//item为高亮状态时调用（当上面的方法返回YES时，此方法才有用）
- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//item取消高亮状态时调用
- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//设置item是否能够选中
- (BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath;
//设置item是否能够取消选中（多选的时候，再次点击则取消选择）
- (BOOL)collectionView:(UICollectionView *)collectionView shouldDeselectItemAtIndexPath:(NSIndexPath *)indexPath; 
//item被选中时调用
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath;
//item被取消选中时调用
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath;

//***这几个方法可以添加简易的动画,例如添加如下几句代码，cell加载的时候将会有放缩等效果。
//将要加载某个item时调用
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//将要加载头尾视图时调用
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//展示完某个item调用
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;
//展示完某个头尾视图调用
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingSupplementaryView:(UICollectionReusableView *)view forElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;


//设置是否展示长按菜单
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath;
//设置点击菜单选项时触发的动作
- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
//设置点击菜单选项时触发的动作
- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;

//对collectionView进行重新布局时调用
- (nonnull UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout;

//以下是在Apple TV上会用到的关于设置焦点的方法（这里我们不做解释，有兴趣的朋友可以自己去研究）
- (BOOL)collectionView:(UICollectionView *)collectionView canFocusItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
- (BOOL)collectionView:(UICollectionView *)collectionView shouldUpdateFocusInContext:(UICollectionViewFocusUpdateContext *)context NS_AVAILABLE_IOS(9_0);
- (void)collectionView:(UICollectionView *)collectionView didUpdateFocusInContext:(UICollectionViewFocusUpdateContext *)context withAnimationCoordinator:(UIFocusAnimationCoordinator *)coordinator NS_AVAILABLE_IOS(9_0);
- (nullable NSIndexPath *)indexPathForPreferredFocusedViewInCollectionView:(UICollectionView *)collectionView NS_AVAILABLE_IOS(9_0);
- (NSIndexPath *)collectionView:(UICollectionView *)collectionView targetIndexPathForMoveFromItemAtIndexPath:(NSIndexPath *)originalIndexPath toProposedIndexPath:(NSIndexPath *)proposedIndexPath NS_AVAILABLE_IOS(9_0);
- (CGPoint)collectionView:(UICollectionView *)collectionView targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset NS_AVAILABLE_IOS(9_0); 
@end

//继承于UIScrollView
NS_CLASS_AVAILABLE_IOS(6_0) @interface UICollectionView : UIScrollView

//初始化一个对象，需要UICollectionViewLayout对象来初始化，系统自带一个UICollectionViewLowLayout也可以自定义
- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout NS_DESIGNATED_INITIALIZER;
//从stordBoard拿出的时候调用
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

//可以设定布局，可以进行重新布局
@property (nonatomic, strong) UICollectionViewLayout *collectionViewLayout;

//代理
@property (nonatomic, weak, nullable) id <UICollectionViewDelegate> delegate;

//代理
@property (nonatomic, weak, nullable) id <UICollectionViewDataSource> dataSource;

//代理
/*这个新的协议属性是UICollectionView和UITableView都支持的。这个协议其实是用来通知我们，
当前滑动到某个区域后，根据这次滑动的方向接下去可能还会滑向哪些indexPaths。好让我们做一些数据上的预备或者销毁。*/
@property (nonatomic, weak, nullable) id<UICollectionViewDataSourcePrefetching> prefetchDataSource NS_AVAILABLE_IOS(10_0);

//是否支持滑动预设
@property (nonatomic, getter=isPrefetchingEnabled) BOOL prefetchingEnabled NS_AVAILABLE_IOS(10_0);

//背景视图,会自动填充整个UICollectionView
@property (nonatomic, strong, nullable) UIView *backgroundView;


//注册Cell
//通过代码创建出的Cell的注册方法
- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;
//通过XIB创建出的Cell的注册方法
- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;
//通过代码创建出的header和footer的注册方法
- (void)registerClass:(nullable Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier;
//通过XIB创建出的header和footer的注册方法
- (void)registerNib:(nullable UINib *)nib forSupplementaryViewOfKind:(NSString *)kind withReuseIdentifier:(NSString *)identifier;
//从队列中找出就可以复用的cell
- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
//从队列中找出就可以复用的head和foot
- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;


//是否允许选中cell，默认允许选中
@property (nonatomic) BOOL allowsSelection;
 // 是否允许多选
@property (nonatomic) BOOL allowsMultipleSelection;

#if UIKIT_DEFINE_AS_PROPERTIES

//只读，返回选择的item
@property (nonatomic, readonly, nullable) NSArray<NSIndexPath *> *indexPathsForSelectedItems; 
#else

//返回已经选择的位置，默认是nil
- (nullable NSArray<NSIndexPath *> *)indexPathsForSelectedItems;

#endif
//带动画选中某个item，可以带滚动效果
- (void)selectItemAtIndexPath:(nullable NSIndexPath *)indexPath animated:(BOOL)animated scrollPosition:(UICollectionViewScrollPosition)scrollPosition;
//带动画取消选中某个item
- (void)deselectItemAtIndexPath:(NSIndexPath *)indexPath animated:(BOOL)animated;

//重新加载所有的数据等
- (void)reloadData; 

//从一个布局过度到另一个布局带动画
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated;

////从一个布局过度到另一个布局带动画，完成后可以自定义
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated completion:(void (^ __nullable)(BOOL finished))completion NS_AVAILABLE_IOS(7_0);

//下面这些方法更加强大，我们可以对布局更改后的动画进行设置
//这个方法传入一个布局策略layout，系统会开始进行布局渲染，返回一个UICollectionViewTransitionLayout对象
//这个UICollectionViewTransitionLayout对象管理动画的相关属性，我们可以进行设置
- (UICollectionViewTransitionLayout *)startInteractiveTransitionToCollectionViewLayout:(UICollectionViewLayout *)layout completion:(nullable UICollectionViewLayoutInteractiveTransitionCompletion)completion NS_AVAILABLE_IOS(7_0);
//准备好动画设置后，我们需要调用下面的方法进行布局动画的展示，之后会调用上面方法的block回调
- (void)finishInteractiveTransition NS_AVAILABLE_IOS(7_0);
//调用这个方法取消上面的布局动画设置，之后也会进行上面方法的block回调
- (void)cancelInteractiveTransition NS_AVAILABLE_IOS(7_0);



#if UIKIT_DEFINE_AS_PROPERTIES
//只读，Sections个数
@property (nonatomic, readonly) NSInteger numberOfSections;
#else

//Sections个数
- (NSInteger)numberOfSections;
#endif
//某个section上item的个数
- (NSInteger)numberOfItemsInSection:(NSInteger)section;


//下面两个方法获取item或者头尾视图的layout属性，这个UICollectionViewLayoutAttributes对象存放着布局的相关数据，可以用来做完全自定义布局
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;

//获取某一点所在的indexpath位置
- (nullable NSIndexPath *)indexPathForItemAtPoint:(CGPoint)point;
//获取某个cell所在的indexPath
- (nullable NSIndexPath *)indexPathForCell:(UICollectionViewCell *)cell;
//根据indexPath获取cell
- (nullable UICollectionViewCell *)cellForItemAtIndexPath:(NSIndexPath *)indexPath;

#if UIKIT_DEFINE_AS_PROPERTIES
//获取所有可见cell的位置数组
@property (nonatomic, readonly) NSArray<__kindof UICollectionViewCell *> *visibleCells;

//获取所有可见cell的位置数组
@property (nonatomic, readonly) NSArray<NSIndexPath *> *indexPathsForVisibleItems;
#else

- (NSArray<__kindof UICollectionViewCell *> *)visibleCells;
- (NSArray<NSIndexPath *> *)indexPathsForVisibleItems;
#endif

//下面三个方法是iOS9中新添加的方法，用于获取头尾视图
- (nullable 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);

//滚动带某个位置
- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated;

//下面这些方法用于动态添加，删除，移动某些分区获取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;

- (void)performBatchUpdates:(void (^ __nullable)(void))updates completion:(void (^ __nullable)(BOOL finished))completion; // allows multiple insert/delete/reload/move calls to be animated simultaneously. Nestable.

//开始在特定的索引路径上对cell（单元）进行Interactive Movement（交互式移动工作），默认不允许
- (BOOL)beginInteractiveMovementForItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0); 

//在手势作用期间更新交互移动的目标位置。
- (void)updateInteractiveMovementTargetPosition:(CGPoint)targetPosition NS_AVAILABLE_IOS(9_0);

//在完成手势动作后，结束交互式移动
- (void)endInteractiveMovement NS_AVAILABLE_IOS(9_0);

//取消Interactive Movement
- (void)cancelInteractiveMovement NS_AVAILABLE_IOS(9_0);

// 支持记忆最后选中的path，如果失去焦点则默认选择上次的焦点
@property (nonatomic) BOOL remembersLastFocusedIndexPath NS_AVAILABLE_IOS(9_0); 

@end

@interface NSIndexPath (UICollectionViewAdditions)

//根据item和section创建一个NSIndexPath对象
+ (instancetype)indexPathForItem:(NSInteger)item inSection:(NSInteger)section NS_AVAILABLE_IOS(6_0);

//返回对象的item
@property (nonatomic, readonly) NSInteger item NS_AVAILABLE_IOS(6_0);

@end

NS_ASSUME_NONNULL_END