class ViewController: UIViewController {

  @IBOutlet weak var toggleButton: UIButton!
  @IBOutlet weak var heightConstraint: NSLayoutConstraint!
  @IBOutlet weak var viewB: UIView!
  var toggle = false


  @IBAction func toggleBLabelConstraint(sender: AnyObject) {
    toggle = !toggle
    if toggle{
      toggleButton.setTitle("Show B", forState: UIControlState.Normal)
      UIView.animateWithDuration(0.3, animations: {
        self.viewB.alpha = 0.7
        self.heightConstraint.constant -= 70
        self.view.layoutIfNeeded()
      })
    }else{
      toggleButton.setTitle("Hide B", forState: UIControlState.Normal)
      UIView.animateWithDuration(0.3, animations: {
        self.viewB.alpha = 1
        self.heightConstraint.constant += 70
        self.view.layoutIfNeeded()
      })
    }
  }
}