ViewController.m

#import "ViewController.h"
@interface ViewController ()<UICollectionViewDelegate,UICollectionViewDataSource>
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    //每一个collectionView必须有个layout
    //layout布局就是collectionView的精华所在
    //不同的layout可以布局不同的界面效果
    //layout是可以自定义的,系统也给我们提供了常用的子类
    //系统提供的UICollectionViewFlowLayout(显示九宫格样式)
    //flowLayout可以实际大部分程序的布局需求所以一般都使用这个layout
    UICollectionViewFlowLayout *flowLayout=[[UICollectionViewFlowLayout alloc]init];
    //设置行间距-最小行间距
    flowLayout.minimumLineSpacing=10;
    //设置每单元格左右间距
    flowLayout.minimumInteritemSpacing=10;
    //滑动的方向
    flowLayout.scrollDirection=UICollectionViewScrollDirectionVertical;
    //设置view的周边间距
    flowLayout.sectionInset=UIEdgeInsetsMake(10, 10, 10, 10);
    //设置单元格的大小
    flowLayout.itemSize=CGSizeMake(50, 50);
    //一个layout对象不能同时用在多个collectionView上
    //创建collectionView
    UICollectionView *collection=[[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:flowLayout];
    //设置代理
    collection.delegate=self;
    //设置数据源
    collection.dataSource=self;
    //展示
    [self.view addSubview:collection];
    //注册UICollectionViewCell
    [collection registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
    /*
    XIB自定义Cell   
 [collectionView registerNib:[UINib nibWithNibName:@"CustomCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"cell"];
*/
}
#pragma mark-UICollectionViewDataSource
\- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 50;
}
- (UICollectionViewCell \*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{

\*    
    XIB自定义Cell
 CustomCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
 */
    //获取通过标识符获取cell
    UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    cell.backgroundColor=[UIColor colorWithRed:arc4random()%255/255.f green:arc4random()%255/255.f blue:arc4random()%255/255.f alpha:1];
    return cell;
}
@end