CollectionViewController.swift

//
//  CollectionViewController.swift
//  ReusableDemo
//
//  Created by Olivier Halligon on 19/01/2016.
//  Copyright © 2016 AliSoftware. All rights reserved.
//

import UIKit

final class CollectionViewController: UICollectionViewController {

  override func viewDidLoad() {
    super.viewDidLoad()
    guard let collectionView = self.collectionView else { return }

    // Register cell classes
    collectionView.register(cellType: MyXIBIndexSquaceCell.self)

    /* Since MyColorSquareCell is marked as conforming to AutoRegistering,
     there's no need to register this type ahead of time */
    //collectionView.register(cellType: MyColorSquareCell.self)

    // No need to register this one, the UIStoryboard already auto-register its cells
    //    self.collectionView.registerReusableCell(MyStoryBoardIndexPathCell)

    collectionView.register(supplementaryViewType: CollectionHeaderView.self,
                            ofKind: UICollectionView.elementKindSectionHeader)

    if let flowLayout = self.collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
      flowLayout.headerReferenceSize = CGSize(width: collectionView.bounds.size.width, height: 60)
    }
  }

  // MARK: UICollectionViewDataSource

  override func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 3
  }

  override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 5
  }

  override func collectionView(_ collectionView: UICollectionView,
                               viewForSupplementaryElementOfKind kind: String,
                               at indexPath: IndexPath) -> UICollectionReusableView {
    let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, for: indexPath) as CollectionHeaderView
      header.title = "Section \(indexPath.section)"
      return header
  }

  override func collectionView(_ collectionView: UICollectionView,
                               cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
      switch indexPath.section {
      case 0:
        let cell = collectionView.dequeueReusableCell(for: indexPath) as MyColorSquareCell
        let red = CGFloat(indexPath.row) / CGFloat(collectionView.numberOfItems(inSection: indexPath.section))
        cell.fill(UIColor(red: red, green: 0.0, blue: 1.0-red, alpha: 1.0))
        return cell
      case 1:
        let cell = collectionView.dequeueReusableCell(for: indexPath) as MyStoryboardTextSquareCell
        cell.fill("Item #\(indexPath.row)")
        return cell
      case 2:
        let cell = collectionView.dequeueReusableCell(for: indexPath) as MyXIBIndexSquaceCell
        cell.fill(indexPath)
        return cell
      default:
        fatalError("Out of bounds, should not happen")
      }
  }
}

/// Swift < 4.2 support
#if !(swift(>=4.2))
private extension UICollectionView {
  static let elementKindSectionHeader = UICollectionElementKindSectionHeader
}
#endif