objective-c - 关于iOS中的动画效果

Question

原文地址：http://www.raywenderlich.com/76147/uikit-dynamics-tutorial-swift
在原文的最下面有这样一段代码，实现的大概效果是：当手指触摸屏幕某一点时，view就移动到那一点，我不是很清楚其中这段if语句，if语句的意思应该是把snap行为移除，可是这有什么作用，为什么把if语句删掉了就不能达到上面的效果

override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {

        if (snap != nil) {
            animator.removeBehavior(snap)
        }
        
        let touch = touches.first! as UITouch
        snap = UISnapBehavior(item: square, snapToPoint: touch.locationInView(view))
        animator.addBehavior(snap)
    }

Answer 1

That is used to block touch points that have not been completed or there is no reset after the event is completed, in response to your last click event.