reason: 'UICollectionView must be initialized with a non-nil layout parameter'

reason: 'UICollectionView must be initialized with a non-nil layout parameter'

Xcode报这个错误的原因是 没有设置UICollectionView的布局

- (instancetype)init

{

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

    // cell的大小

    layout.itemSize = CGSizeMake(305, 305);

    return [self initWithCollectionViewLayout:layout];

}