Nest a UICollectionView inside a UIVIew programmatically

Question

I am attempting to get a UICollectionView to be inside a UIView as the framework I'm using requires a UIView to be returned. I have looked at this question: How do I add a UICollectionView to a UIView as a subview? and Adding UICollectionView inside UIView without Storyboards but not sure how to get it to work.

I have a attempted it like this:

class TopView : UIView, UICollectionViewDataSource, UICollectionViewDelegate {

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = .red

        addSubview(collectionView)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    lazy var collectionView : UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let cv = UICollectionView(frame: CGRect.zero, collectionViewLayout: layout)
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.delegate = self
        cv.dataSource = self
        cv.register(HeaderCell.self, forCellWithReuseIdentifier: "HeaderCell")
        cv.backgroundColor = .yellow

        return cv
    }()

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HeaderCell", for: indexPath) as! HeaderCell

        return cell

    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: self.collectionView.frame.width, height: 200)
    }

    func collectionView(_ collectionView: UICollectionView, numberOfSections section: Int) -> Int {
        return 1
    }

}

But I'm getting a blank screen.

Update:

This is how I add the TopView to a UIViewController:

class MainViewController: UIViewController {

    var mainView = TopView()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(mainView)
    }
}

I get just a black screen.

Answer 1

TopView.swift

class TopView : UIView, UICollectionViewDataSource, UICollectionViewDelegate {

    lazy var collectionView : UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let cv = UICollectionView(frame: CGRect.zero, collectionViewLayout: layout)
        //If you set it false, you have to add constraints.
        cv.translatesAutoresizingMaskIntoConstraints = false 
        cv.delegate = self
        cv.dataSource = self
        cv.register(HeaderCell.self, forCellWithReuseIdentifier: "HeaderCell")
        cv.backgroundColor = .yellow
        return cv
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)

        self.backgroundColor = .red

        addSubview(collectionView)

        //Add constraint
        collectionView.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true
        collectionView.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true
        collectionView.topAnchor.constraint(equalTo: topAnchor).isActive = true
        collectionView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    func collectionView(_ collectionView: UICollectionView, numberOfSections section: Int) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 30
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HeaderCell", for: indexPath) as! HeaderCell
        cell.backgroundColor = .cyan
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: self.collectionView.frame.size.width, height: 200)
    }    
}

ViewController.swift

lazy var topView: TopView = {
    let tv = TopView()
    tv.translatesAutoresizingMaskIntoConstraints = false
    return tv
}()

func addTopView() {
    view.addSubview(topView)

    topView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
    topView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
    topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 300).isActive = true
    topView.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
    topView.heightAnchor.constraint(equalToConstant: 200).isActive = true
}

Call addTopView() from viewDidLoad()