invalid_collectionview.swift

//
//  ViewController.swift
//  TableViewInvalidSample
//
//  Created by Kazuya Ueoka on 2020/06/23.
//  Copyright © 2020 fromKK. All rights reserved.
//

import UIKit

final class Cell: UICollectionViewCell {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setUp()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setUp()
    }
    
    private lazy var setUp: () -> Void = {
        textLabel.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(textLabel)
        NSLayoutConstraint.activate([
            textLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 16),
            textLabel.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 16),
            contentView.trailingAnchor.constraint(equalTo: textLabel.trailingAnchor, constant: 16),
            contentView.bottomAnchor.constraint(equalTo: textLabel.bottomAnchor, constant: 16)
        ])
        return {}
    }()
    
    lazy var textLabel: UILabel = {
        let label = UILabel()
        label.font = UIFont.systemFont(ofSize: 16)
        label.textColor = .black
        return label
    }()

}

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(collectionView)
        NSLayoutConstraint.activate([
            collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            collectionView.topAnchor.constraint(equalTo: view.topAnchor),
            view.trailingAnchor.constraint(equalTo: collectionView.trailingAnchor),
            view.bottomAnchor.constraint(equalTo: collectionView.bottomAnchor)
        ])
    }
    
    private lazy var layout: UICollectionViewFlowLayout = {
        let layout = UICollectionViewFlowLayout()
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        layout.scrollDirection = .vertical
        return layout
    }()

    lazy var collectionView: UICollectionView = {
        let collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.backgroundColor = .white
        collectionView.register(Cell.self, forCellWithReuseIdentifier: "Cell")
        collectionView.dataSource = self
        collectionView.delegate = self
        return collectionView
    }()
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 3
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
        cell.textLabel.text = String(format: "%d - %d", indexPath.section, indexPath.item)
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        switch indexPath.section {
//        case 1:
//            return .zero
        default:
            return CGSize(width: collectionView.bounds.size.width, height: 60)
        }
    }
}