ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UICollectionViewDataSource,UICollectionViewDelegateFlowLayout>

@property (strong, nonatomic)UICollectionView *collectionView;

@end

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    UICollectionViewFlowLayout *flowLayout=[[UICollectionViewFlowLayout alloc] init];
    [flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
    
    self.collectionView=[[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, 320, 240) collectionViewLayout:flowLayout];
    self.collectionView.dataSource=self;
    self.collectionView.delegate=self;
    [self.collectionView setBackgroundColor:[UIColor grayColor]];
    
    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"UICollectionViewCell"];
    [self.view addSubview:self.collectionView];
}

#pragma mark -- UICollectionViewDataSource

//定义展示的UICollectionViewCell的个数
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 10;
}

//定义展示的Section的个数
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 2;
}

//每个UICollectionView展示的内容
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString * CellIdentifier = @"UICollectionViewCell";
    UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
    
    cell.backgroundColor = [UIColor colorWithRed:((10 * indexPath.row) / 255.0) green:((20 * indexPath.row)/255.0) blue:((30 * indexPath.row)/255.0) alpha:1.0f];
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
    label.textColor = [UIColor redColor];
    label.text = [NSString stringWithFormat:@"%d",indexPath.row];
 
    for (id subView in cell.contentView.subviews) {
        [subView removeFromSuperview];
    }
    [cell.contentView addSubview:label];
    return cell;
}

#pragma mark --UICollectionViewDelegateFlowLayout

//定义每个Item 的大小
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(80, 80);
}

//定义每个UICollectionView 的 margin
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    return UIEdgeInsetsMake(5, 5, 5, 5);
}

#pragma mark --UICollectionViewDelegate

//UICollectionView被选中时调用的方法
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell * cell = (UICollectionViewCell *)[collectionView cellForItemAtIndexPath:indexPath];
    cell.backgroundColor = [UIColor whiteColor];
}

//返回这个UICollectionView是否可以被选择
-(BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}


@end