Resize views in `viewWillLayoutSubviews`

gistfile1.swift

class ViewController: UIViewController {

    var redView: UIView!
    var greenView: UIView!
    var blueView: UIView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        redView = UIView()
        redView.backgroundColor = UIColor.redColor()
        view.addSubview(redView)
        
        blueView = UIView()
        blueView.backgroundColor = UIColor.blueColor()
        view.addSubview(blueView)
        
        greenView = UIView()
        greenView.backgroundColor = UIColor.greenColor()
        view.addSubview(greenView)
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        
        redView.frame = CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height / 3.0)
        greenView.frame = CGRect(x: 0, y: view.frame.size.height * 1.0 / 3.0, width: view.frame.size.width, height: view.frame.size.height / 3.0)
        blueView.frame = CGRect(x: 0, y: view.frame.size.height * 2.0 / 3.0, width: view.frame.size.width, height: view.frame.size.height / 3.0)
    }
    
}