Horizontal_PickerView.swift

class AddSetViewController: UIViewController {
    @IBOutlet weak var RepsPickerView: UIPickerView!
    var rotationAngle: CGFloat!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        rotationAngle = -90 * (.pi / 180)
        
        let y = RepsPickerView.frame.origin.y
        RepsPickerView.transform = CGAffineTransform(rotationAngle: rotationAngle)
        RepsPickerView.frame = CGRect(x: -100, y: y, width: view.frame.width + 200, height: 80)
    }
}

class RepsPickerView: UIPickerView, UIPickerViewDelegate, UIPickerViewDataSource {
    private var reps = Array(0...100)
    private var selectedRep: Int!
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.commonSetup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.commonSetup()
    }
    
    func commonSetup() {
        self.delegate = self
        self.dataSource = self
    }
    
    func onSelected() -> Int {
        return self.selectedRep
    }
    
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return 100
    }
    
    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        self.selectedRep = reps[row]
    }
    
    func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
        let view = UIView(frame: CGRect(x: 0, y: 0, width: 50, height: 50))
        let label = UILabel(frame: CGRect(x: 0, y: 10, width: 50, height: 50))
        label.text = String(reps[row])
        label.textAlignment = .center
        label.font = UIFont.systemFont(ofSize: 16, weight: .semibold)
        view.addSubview(label)
        
        view.transform = CGAffineTransform(rotationAngle: (90 * .pi/180))
        return view
    }
    
}