class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var aView = UIView()
        aView.backgroundColor = UIColor.redColor()
        aView.setTranslatesAutoresizingMaskIntoConstraints(false)
        self.view .addSubview(aView)
        
        //新增約束
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-[aView]-|", options: .DirectionLeadingToTrailing, metrics: nil, views: ["aView":aView]))
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-20-[aView(==50)]|", options: .DirectionLeadingToTrailing, metrics: nil, views: ["aView":aView]))
    }

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