UIConllectionViewController

写个类继承 UICollectionViewController

并设置成 rootViewController

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

  XuCollectionViewController *xu = [[XuCollectionViewController alloc]init];
  self.window.rootViewController = xu;
  return YES;
  }

  这是 .h 文件
  #import

@interface XuCollectionViewController : UICollectionViewController

@end

这是 .m 文件

• (void)viewDidLoad {
  [super viewDidLoad];

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

  [layout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
  //cell间距
  layout.minimumInteritemSpacing = 5.0f;
  //cell行距
  layout.minimumLineSpacing = 1.0f;
  [layout setItemSize:CGSizeMake(30, 30)];
  
  self.collectionView = [[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:layout];

}

运行时 会崩溃 'UICollectionView must be initialized with a non-nil layout parameter'

一直没找到原因 ，哪位大神 给看下。