【Swift】CollectionView【コピペコード】

【「ViewController」のコード】

import UIKit

class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout {
    
    private let collectionView = UICollectionView(
        frame: .zero,
        collectionViewLayout: UICollectionViewFlowLayout()
    )

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.register(PhotoCollectionViewCell.self, forCellWithReuseIdentifier: PhotoCollectionViewCell.identifier)
        collectionView.delegate = self
        collectionView.dataSource = self
        view.addSubview(collectionView)
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        collectionView.frame = view.bounds
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 30
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PhotoCollectionViewCell.identifier, for: indexPath)
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: (view.frame.size.width/3)-3,
                      height: (view.frame.size.width/3)-3
        )
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: 1, left: 1, bottom: 1, right: 1)
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        collectionView.deselectItem(at: indexPath, animated: true)
        print("Selected section \(indexPath.section) and row \(indexPath.row)")
    }

}

【「PhotoCollectionViewCell」のコード】

import UIKit

class PhotoCollectionViewCell: UICollectionViewCell {
    static let identifier = "PhotoCollectionViewCell"
    
    private let imageView: UIImageView = {
        let imageView = UIImageView()
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        return imageView
    }()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.addSubview(imageView)
        
        let images = [
            UIImage(named: "Bar1"),
            UIImage(named: "Bar2"),
            UIImage(named: "Bar3"),
            UIImage(named: "Bar4"),
            UIImage(named: "Bar5"),
            UIImage(named: "Bar6")
        ].compactMap({ $0 })
        imageView.image = images.randomElement()
    }
    
    required init?(coder: NSCoder) {
        fatalError()
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        imageView.frame = contentView.bounds
    }
    
    override func prepareForReuse() {
        super.prepareForReuse()
        // imageView.image = nil
    }
    
}

参考動画

Create Collection View for Beginners (Swift 5, Xcode 12, iOS) - 2020 iOS Development
https://www.youtube.com/watch?v=_OkriRP8Vx8&t=51s