IOS学习 collectionView 的创建

@implementation HomeViewController

//定义重用标识符

static NSString *identifier =
@"collectionCell";

- (void)viewDidLoad {

[super
viewDidLoad];

// Do any additional setup after loading the view.

/*

collectionView 必须有一个layout

在storyboard上拖拽的时候，已经自动增加一个
流水布局

UICollectionView must be initialized with a non-nil layout parameter

实例化一个layout对象:collectionView如果要实例化一个layout，必须在实例化的时候就进行设置

UICollectionViewLayout 是流水布局的父类，是最纯净的layout

UICollectionViewFlowLayout 在父类上做了扩展

*/

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout
alloc]init];

//修改cell的大小
默认宽高为50

flowLayout.itemSize =
CGSizeMake(100,
100);

//实例化一个collectionView

UICollectionView *collectionView = [[UICollectionView
alloc]initWithFrame:self.view.bounds
collectionViewLayout:flowLayout];

[self.view
addSubview:collectionView];

//设置代理

collectionView.dataSource =
self;

collectionView.delegate =
self;

//注册一个collectionCell

[collectionView registerClass:[UICollectionViewCell
class] forCellWithReuseIdentifier:identifier];

//设置背景色

collectionView.backgroundColor = [UIColor
whiteColor];

}

//组

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{

return
1;

}

//行

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{

return
100;

}

//每一行的内容

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath
*)indexPath{

//从缓存池中去找

UICollectionViewCell *cell = [collectionView
dequeueReusableCellWithReuseIdentifier:identifier
forIndexPath:indexPath];

cell.backgroundColor = [UIColor
redColor];

return cell;

}

//取消选中

- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath
*)indexPath{

NSLog(@"取消选中 - %ld",indexPath.item);

}

//被选中

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath
*)indexPath{

//item 相当于row

NSLog(@"选中 - %ld",indexPath.item);

}