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

Question

I added UICollectionView by code.
Now, the app crash with message: UICollectionView must be initialized with a non-nil layout parameter.
Do

Answer 1

Just a swift version of Riley Avron's answer

    let layout = UICollectionViewFlowLayout()
    layout.itemSize = CGSizeMake(100, 100)
    let collectionView = UICollectionView(frame: CGRectZero, collectionViewLayout: layout)
    self.view.addSubview(collectionView)
    collectionView.delegate   = self
    collectionView.dataSource = self
    collectionView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: "cellIdentifier")