Collection View In Code

viewController.swift

//: Playground - noun: a place where people can play

import UIKit
import PlaygroundSupport

class MyViewController: UIViewController {

  let collectionView: UICollectionView
  let flowLayout: UICollectionViewFlowLayout

  init() {
    flowLayout = UICollectionViewFlowLayout()
    collectionView = UICollectionView(frame: CGRect.zero, collectionViewLayout: flowLayout)
    super.init(nibName: nil, bundle: nil)
    setup()
  }

  override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    setupFlowLayout()
  }
  
  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  private func setup() {
    collectionView.delegate = self
    collectionView.dataSource = self
    view.backgroundColor = .white
    view.addSubview(collectionView)

    collectionView.backgroundColor = .white
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
    collectionView.collectionViewLayout = flowLayout
    collectionView.translatesAutoresizingMaskIntoConstraints = false
    collectionView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
    collectionView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
    collectionView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
    collectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
  }

  private func setupFlowLayout() {
    flowLayout.itemSize = CGSize(width: view.bounds.width - 40, height: 100)
    flowLayout.minimumLineSpacing = 10
    flowLayout.minimumInteritemSpacing = 0
  }

}

extension MyViewController: UICollectionViewDelegate {
  func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    print(indexPath)
  }
}

extension MyViewController: UICollectionViewDataSource {
  func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 1
  }
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 10
  }
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as UICollectionViewCell
    cell.backgroundColor = .red
    return cell
  }
}

let vc = MyViewController()

PlaygroundPage.current.liveView = vc