iOS UICollectionView

The UICollectionView class manages an ordered collection of data items and presents them using customizable layouts. Collection views provide the same general function as table views except that a collection view is able to support more than just single-column layouts. Collection views support customizable layouts that can be used to implement multi-column grids, tiled layouts, circular layouts, and many more. You can even change the layout of a collection view dynamically if you want.

以上就是苹果对UICollectionView的一个简单介绍，它是iOS 6.0后出现的新UI控件，和UITableView非常相似，但它可以实现多列布局，有自定义布局的特性用于实现网格视图，瓦片视图(在学cocos时习惯这么称呼)，环形视图和更多你能想到的，甚至可以动态的修改这个集合布局。对了，因此也可以利用它做出横向UITableView的效果，总之它给开发者的感觉应该比UITableView更胜一筹。

首先尝试实现一个简单的九宫格：

static NSString *identifie = @"cell";@interface VerticalViewController ()<UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout>{    NSArray *images;}@end@implementation VerticalViewController- (void)viewDidLoad {    [super viewDidLoad];    self.view.backgroundColor = [UIColor whiteColor];    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc]init];    layout.scrollDirection = UICollectionViewScrollDirectionVertical;//垂直布局滚动    layout.itemSize = CGSizeMake((self.view.bounds.size.width-20)/3, 100);//每个cell的大小    _collectionView = [[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:layout];    _collectionView.delegate = self;    _collectionView.dataSource = self;    [_collectionView registerClass:[ItemCell class] forCellWithReuseIdentifier:identifie];    [self.view addSubview:_collectionView];}- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{    return 1;}- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{    return 50;}- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    ItemCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifie forIndexPath:indexPath];    cell.backgroundColor = [UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0 blue:arc4random()%256/255.0 alpha:1];    return cell;}

UICollectionViewFlowLayout类继承自UICollectionViewLayout，它负责组织和定位每个cell在collection view里的填充样式。但实际上这个layout对象并没有被应用到相应的view上，因为cell的创建和追加的view(例如头视图和尾视图)需要在collection view和数据源之间做协调，collection view才实际运用这些到所有的子view上。所以，某种意义上看，layout对象更像另一个数据源，只是提供每个item(cell)视觉上的信息。
个人感觉差不多就是决定UICollectionView布局的基本信息就是了。
它的scrollDirection属性默认就是UICollectionViewScrollDirectionVertical，垂直方向布局和滚动，还有横向的UICollectionViewScrollDirectionHorizontal。

水平修改可以这样：

layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;layout.itemSize = CGSizeMake(140, (self.view.bounds.size.height-64-90)/10);//因为这个界面是UINavigationController推进来的，所以进去导航栏加通知栏的总高度64

效果图如下左垂直，右水平。。。虽然这么看不太明显:

       

还有很多UICOllectionView相关的方法和属性:

//获取和设置collection的layout@property (nonatomic, strong) UICollectionViewLayout *collectionViewLayout;//从一个class或者xib文件进行cell(item)的注册- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;//下面两个方法与上面相似，这里注册的是头视图或者尾视图的类//其中第二个参数是设置 头视图或者尾视图 系统为我们定义好了这两个字符串//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;//这两个方法是从复用池中取出cell或者头尾视图- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;//设置是否允许选中 默认yes@property (nonatomic) BOOL allowsSelection;//设置是否允许多选 默认no@property (nonatomic) BOOL allowsMultipleSelection;//获取所有选中的item的位置信息- (nullable NSArray<NSIndexPath *> *)indexPathsForSelectedItems; //设置选中某一item，并使视图滑动到相应位置，scrollPosition是滑动位置的相关参数，如下：/*typedef NS_OPTIONS(NSUInteger, UICollectionViewScrollPosition) {    //无    UICollectionViewScrollPositionNone                 = 0,    //垂直布局时使用的 对应上中下    UICollectionViewScrollPositionTop                  = 1 << 0,    UICollectionViewScrollPositionCenteredVertically   = 1 << 1,    UICollectionViewScrollPositionBottom               = 1 << 2,    //水平布局时使用的  对应左中右    UICollectionViewScrollPositionLeft                 = 1 << 3,    UICollectionViewScrollPositionCenteredHorizontally = 1 << 4,    UICollectionViewScrollPositionRight                = 1 << 5};*/- (void)selectItemAtIndexPath:(nullable NSIndexPath *)indexPath animated:(BOOL)animated scrollPosition:(UICollectionViewScrollPosition)scrollPosition;//将某一item取消选中- (void)deselectItemAtIndexPath:(NSIndexPath *)indexPath animated:(BOOL)animated;//重新加载数据- (void)reloadData;//下面这两个方法，可以重新设置collection的布局，后面的方法多了一个布局完成后的回调，iOS7后可以用//使用这两个方法可以产生非常炫酷的动画效果- (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);//获取分区数- (NSInteger)numberOfSections;//获取某一分区的item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，后面博客会介绍- (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;//获取所有可见cell的数组- (NSArray<__kindof UICollectionViewCell *> *)visibleCells;//获取所有可见cell的位置数组- (NSArray<NSIndexPath *> *)indexPathsForVisibleItems;//用于获取头尾视图- (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);//使视图滑动到某一位置，可以带动画效果- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated;//下面这些方法用于动态添加，删除，移动分区或者item- (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;//批量任务，可以用于排序- (void)performBatchUpdates:(void (^ __nullable)(void))updates completion:(void (^ __nullable)(BOOL finished))completion;//开始拖拽某个cell时调用此方法,并把将被拖拽的cell的indexPath传入方法- (BOOL)beginInteractiveMovementForItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0); // returns NO if reordering was prevented from beginning - otherwise YES//可以在手势移动过程中交换item位置- (void)updateInteractiveMovementTargetPosition:(CGPoint)targetPosition NS_AVAILABLE_IOS(9_0);//手势结束时调用,结束拖拽- (void)endInteractiveMovement NS_AVAILABLE_IOS(9_0);//手势取消时调用,取消拖拽- (void)cancelInteractiveMovement NS_AVAILABLE_IOS(9_0);// 记住最后被focus的item位置@property (nonatomic) BOOL remembersLastFocusedIndexPath NS_AVAILABLE_IOS(9_0);