convertir TextField a Int



class BMICalculator: UIViewController {
    //MARK: Properties
    @IBOutlet weak var weightField: UITextField!
    @IBOutlet weak var heightField: UITextField!
    @IBOutlet weak var solutionTextField: UILabel!

    @IBAction func calcButton(_ sender: AnyObject) {
    let weightInt = Int((weightField?.text!)!)
    let heightInt = Int((heightField?.text!)!)

    let solution = weightInt!/(heightInt!*heightInt!)

    solutionTextField?.text = "\(solution)"

    override func viewDidLoad() {

    override func didReceiveMemoryWarning() {
        // Dispose of any resources that can be recreated.