#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

#import "AppDelegate.h"

#import "RootViewController.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    // Override point for customization after application launch.

    self.window.backgroundColor = [UIColor whiteColor];

    self.window.rootViewController = [[RootViewController alloc] init];

    [self.window makeKeyAndVisible];

    return YES;

}

@end

#import <UIKit/UIKit.h>

@interface RootViewController : UIViewController

@end

#import "RootViewController.h"

@interface RootViewController ()<UICollectionViewDataSource,UICollectionViewDelegate>

{

}

@end

 static NSString *identifier = @"cell";

@implementation RootViewController

- (void)viewDidLoad {

    [super viewDidLoad];

   //创建布局对象

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

    // 设置滚动的方向

    [layout setScrollDirection:UICollectionViewScrollDirectionVertical];

    //行的间隙

    layout.minimumLineSpacing = ;

    //列的间隙

//    layout.minimumInteritemSpacing = 10;

    //item的大小

    layout.itemSize = CGSizeMake([UIScreen mainScreen].bounds.size.width, );

    //创建collectionView

    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:[[UIScreen mainScreen] bounds] collectionViewLayout:layout];

    collectionView.backgroundColor = [UIColor greenColor];

    // 设置代理

    collectionView.dataSource = self;

    collectionView.delegate = self;

    //告诉系统将来需要创建什么样的cell(在获取cell之前必须先注册一个cell到系统中)

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

    [self.view addSubview:collectionView];

}

// 告诉系统一共有多少组

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

    return ;

}

// 告诉系统第section组有多少行

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

    return ;

}

// 告诉系统indexPath的第Section组的item行显示什么内容

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

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

    cell.backgroundColor = [UIColor redColor];

    return cell;

}

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

    NSLog(@"==%lu",indexPath.row);

}

@end