ViewController.swift

import UIKit

class SimpleCollectionViewCell: UICollectionViewCell {
    
    @IBOutlet weak var titleLabel: UILabel!
    
    func bind(color: String) {
        titleLabel.text = "\(arc4random_uniform(1000))"
        backgroundColor = .clear
        contentView.backgroundColor = color.hexColor
    }
}

extension String {
    var hexColor: UIColor {
        let hex = trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
        var int = UInt32()
        Scanner(string: hex).scanHexInt32(&int)
        let a, r, g, b: UInt32
        switch hex.characters.count {
        case 3: // RGB (12-bit)
            (a, r, g, b) = (255, (int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17)
        case 6: // RGB (24-bit)
            (a, r, g, b) = (255, int >> 16, int >> 8 & 0xFF, int & 0xFF)
        case 8: // ARGB (32-bit)
            (a, r, g, b) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF)
        default:
            return .clear
        }
        return UIColor(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
    }
}

class ViewController: UICollectionViewController {
    
    let cellIdentifier = "SimpleCollectionViewCell"
    let vcs = ["f44336", "9c27b0", "3f51b5", "03a9f4", "009688", "8bc34a"]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        // Must turn paging on.
class SimpleCollectionViewCell: UICollectionViewCell {
    
    @IBOutlet weak var titleLabel: UILabel!
    
    func bind(color: String) {
        titleLabel.text = "\(arc4random_uniform(1000))"
        backgroundColor = .clear
        contentView.backgroundColor = color.hexColor
    }
}

extension String {
    var hexColor: UIColor {
        let hex = trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
        var int = UInt32()
        Scanner(string: hex).scanHexInt32(&int)
        let a, r, g, b: UInt32
        switch hex.characters.count {
        case 3: // RGB (12-bit)
            (a, r, g, b) = (255, (int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17)
        case 6: // RGB (24-bit)
            (a, r, g, b) = (255, int >> 16, int >> 8 & 0xFF, int & 0xFF)
        case 8: // ARGB (32-bit)
            (a, r, g, b) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF)
        default:
            return .clear
        }
        return UIColor(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
    }
}

class ViewController: UICollectionViewController {
    
    let cellIdentifier = "SimpleCollectionViewCell"
    let vcs = ["f44336", "9c27b0", "3f51b5", "03a9f4", "009688", "8bc34a"]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        // Must turn paging on.
        collectionView?.isPagingEnabled = true
    }
}

extension ViewController: UICollectionViewDelegateFlowLayout {
    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return vcs.count
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let c = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath)
        
        if let cell = c as? SimpleCollectionViewCell {
            let v = vcs[indexPath.row]
            cell.bind(color: v)
        }
        
        return c
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return view.bounds.size
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return .zero
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }
}
}