UICollectionView简介
UICollectionView在iOS6.0以后引进,与UITableView比较相似。但是UICollectionView将布局完全交给UICollectionViewLayout，而且允许用户自定义layout来进行布局。使其功能比UITableView更加强大、布局更加灵活，迅速在各大APP广泛使用。
本篇将对UICollectionView的使用进行简单介绍，主要包括UICollectionView的视图组成、数据源、常用代理方法以及UICollectionViewFlowLayout的使用。下一遍将会详细讲解UICollectionViewLayout的自定义布局。
UICollectionView的视图组成：
UICollectionView由cell视图、Supplementary View和Decoration View三部分组成。
cell视图
这个大家应该都很清楚，UICollectionView主要内容展示的视图
Supplementary View
对于每组section的信息视图，类似于UITableView的header或者footer
Decoration View
装饰视图，好像很少使用
cell视图跟Supplementary View使用是需要先进行注册以便实现复用：
注册cell的方法，第一个是代码创建，第二个是xib创建
- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;
注册Supplementary View的方法，第一个是代码创建，第二个是xib创建
- (void)registerClass:(nullable Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forSupplementaryViewOfKind:(NSString *)kind withReuseIdentifier:(NSString *)identifier;
在数据源回调中复用的方法：
- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
***上面方法的的kind和elementKind参数用来区分是头部视图还是尾部视图
UICollectionView的数据源代理方法：
//必须实现的数据源代理
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section;
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;
//可选数据源代理
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView;
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
处理移动相关（详细使用看demo）
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath NS_AVAILABLE_IOS(9_0);
UICollectionView的常用代理方法：
//点击cell高亮相关
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//cell选中相关
- (BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView shouldDeselectItemAtIndexPath:(NSIndexPath *)indexPath; // called when the user taps on an already-selected item in multi-select mode
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath;
//cell以及Supplementary View绘制相关
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingSupplementaryView:(UICollectionReusableView *)view forElementOfKind:(NSString *)elementKind atIndexPath:(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。
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0)
{
cell.contentView.alpha = 0;
cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(0, 0), 0);
[UIView animateKeyframesWithDuration:.5 delay:0.0 options:0 animations:^{
/**
* 分步动画 第一个参数是该动画开始的百分比时间 第二个参数是该动画持续的百分比时间
*/
[UIView addKeyframeWithRelativeStartTime:0.0 relativeDuration:0.8 animations:^{
cell.contentView.alpha = .5;
cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(1.2, 1.2), 0);
}];
[UIView addKeyframeWithRelativeStartTime:0.8 relativeDuration:0.2 animations:^{
cell.contentView.alpha = 1;
cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(1, 1), 0);
}];
} completion:^(BOOL finished) {
}];
}
//长按显示菜单相关：(demo中有详细使用)
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
//转场相关（下一篇会讲解）
- (nonnull UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout;
UICollectionViewFlowLayout && UICollectionViewLayout：
UICollectionView之所以比UITableView强大，主要在于其精髓UICollectionViewLayout的布局。它通过 UICollectionViewLayoutAttributes 类来管理 cell 、 Supplementary View 和 Decoration View 的 位置 、 transform 、 alpha 、 hidden 等等。先看看系统为我们提供的UICollectionViewFlowLayout布局的使用吧。
UICollectionViewFlowLayout 的常用属性
//决定了每行的间隔
@property (nonatomic) CGFloat minimumLineSpacing;
//决定了Item之间的间隔
@property (nonatomic) CGFloat minimumInteritemSpacing;
//cell的大小（如果实现的代理该设置无效）
@property (nonatomic) CGSize itemSize;
//cell大小的预计算
@property (nonatomic) CGSize estimatedItemSize NS_AVAILABLE_IOS(8_0); // defaults to CGSizeZero - setting a non-zero size enables cells that self-size via -preferredLayoutAttributesFittingAttributes:
//布局的方向
@property (nonatomic) UICollectionViewScrollDirection scrollDirection; // default is UICollectionViewScrollDirectionVertical
//头视图跟尾视图的大小（横向的时候，headerReferenceSize.width有效，headerReferenceSize.height无效。纵向时相反）
@property (nonatomic) CGSize headerReferenceSize;
@property (nonatomic) CGSize footerReferenceSize;
//间距
@property (nonatomic) UIEdgeInsets sectionInset;
// Set these properties to YES to get headers that pin to the top of the screen and footers that pin to the bottom while scrolling (similar to UITableView).
@property (nonatomic) BOOL sectionHeadersPinToVisibleBounds NS_AVAILABLE_IOS(9_0);
@property (nonatomic) BOOL sectionFootersPinToVisibleBounds NS_AVAILABLE_IOS(9_0);
UICollectionViewFlowLayout 的代理方法
//基本就是上面的属性通过代理的方法返回
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section;
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section;
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section;
