下面这段代码是，单击手势，imageView 跟着手势移动， 但是下面的代码没看懂，求解释

 @IBAction func handlePanGesture(sender: UIPanGestureRecognizer) {

        var translation = sender.translationInView(self.view)
        sender.view!.center = CGPointMake(sender.view!.center.x + translation.x,
            sender.view!.center.y + translation.y)
        sender.setTranslation(CGPointMake(0, 0), inView: self.view)

    }