override func viewDidLoad() {
        super.viewDidLoad()
        
        let redView = UIView(frame: CGRect(x: 0, y: 0, width: self.view.bounds.size.width / 2, height: self.view.bounds.size.height / 2))
        redView.backgroundColor = UIColor.redColor()
        self.view.addSubview(redView)
        
//        redView.transform = CGAffineTransformMakeRotation(CGFloat(M_PI_2))
        
        //瞬間觸發(fā): 作用時間短, 位移相對小, 一般只會觸發(fā)一次
        //tap/swipe
        //持續(xù)觸發(fā): 作用時間長或位移相對大, 會定時或相隔一段距離觸發(fā)
        //pinch/rotate/long press/pan
        
        //快速滑動，在屏幕上停留時間短，距離相對較長
        //每一手勢對象對應一個方向
        let leftSwipe = UISwipeGestureRecognizer(target: self, action: #selector(swipe(_:)))
        leftSwipe.direction = .Left //滑向某個方向
        self.view.addGestureRecognizer(leftSwipe)
    }
    
    func swipe(sender: UISwipeGestureRecognizer) {
        print("left")
    }