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

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

Xcode報這個錯誤的原因是 沒有設置UICollectionView的佈局

- (instancetype)init

{

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

    // cell的大小

    layout.itemSize = CGSizeMake(305, 305);

    return [self initWithCollectionViewLayout:layout];

}