A UIKit UIView with programmatic Auto Layout based layout

ActivitiesListContentView.swift

class ActivitiesListContentView: UIView {
  var flowLayout: ActivitiesListFlowLayout? {
    collectionView.collectionViewLayout as? ActivitiesListFlowLayout
  }

  private(set) lazy var collectionView = UICollectionView(frame: .zero, collectionViewLayout: ActivitiesListFlowLayout())
  private(set) var categorySelectorView: UIView?
  private lazy var categorySelectorContainerView = UIView.autolayoutView()
  
  override init(frame: CGRect) {
    super.init(frame: frame)
    setupViews()
  }
  
  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    flowLayout?.setEstimatedSize(constrainedToWidth: collectionView.bounds.width)
  }
}

extension ActivitiesListContentView {
  func embedCategorySelector(_ view: UIView) {
    guard !subviews.contains(view) else {
      return
    }
    categorySelectorContainerView.addSubview(view)
    view.snp.makeConstraints {
      $0.edges.equalToSuperview()
    }
    categorySelectorView = view
  }
}

// MARK: - Private Methods
private extension ActivitiesListContentView {
  func setupViews() {
    setupCategorySelectorContainerView()
    setupCollectionView()
  }
  
  func setupView() {
    backgroundColor = .white
  }

  func setupCategorySelectorContainerView() {
    addSubview(categorySelectorContainerView)
    categorySelectorContainerView.snp.makeConstraints {
      $0.leading.trailing.equalToSuperview()
      $0.top.equalToSuperview().inset(16)
    }
  }
  
  func setupCollectionView() {
    addSubview(collectionView)
    collectionView.snp.makeConstraints {
      $0.leading.trailing.bottom.equalToSuperview()
      $0.top.equalTo(categorySelectorContainerView.snp.bottom).offset(16)
    }
    collectionView.backgroundColor = .clear
    collectionView.register(ActivitiesListCell.self)
    collectionView.setContentHuggingPriority(.defaultLow, for: .vertical)
  }
}