UIKit Dynamics +快照行为+平移手势=视线颤抖

Question

我尝试用可刷卡片制作像ui一样的火种。为了使ui更好，我添加了捕捉行为以进行查看，因此在滑动手势后返回动画。

问题是在手势期间有时会看到颤抖和眨眼

捕获视频，可以在第二次尝试时看到https://youtu.be/V9Yvg-Fkh14

代码正在关注

class RegistrationSwipeQuestionsViewController:BaseViewController {

var activeView:SwipeableQuestion?
var originalPoint:CGPoint?
var snap: UISnapBehavior!
var animator:UIDynamicAnimator!

lazy var firstView:SwipeableQuestion = {
    var view = SwipeableQuestion()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.backgroundColor = UIColor(red: 72/255, green: 229/255, blue: 136/255, alpha: 1.0)
    return view
}()

override func viewDidLoad() {
    super.viewDidLoad()

    view.addSubview(firstView)

    animator = UIDynamicAnimator(referenceView: view)

    firstView.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
    firstView.centerYAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
    firstView.widthAnchor.constraintEqualToConstant(250).active = true
    firstView.heightAnchor.constraintEqualToConstant(300).active = true

    firstView.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: "pan:"))

    activeView = firstView
}

func pan(gesture:UIPanGestureRecognizer) {

    let translation = gesture.translationInView(activeView)

    switch gesture.state {
    case .Began:
        self.originalPoint = activeView!.center
    case .Changed:
        let rotationStrength = min(CGFloat(translation.x) / 320, 1)
        let rotationAngel =  2 * CGFloat(M_PI) * rotationStrength / 64
        let scaleStrength = 1 - CGFloat(rotationStrength) / 4
        let scale = max(scaleStrength, 1)
        activeView!.center = CGPointMake(self.originalPoint!.x + translation.x, self.originalPoint!.y + translation.y);
        let transform = CGAffineTransformMakeRotation(rotationAngel)
        let scaleTransform = CGAffineTransformScale(transform, scale, scale)
        activeView!.transform = scaleTransform

        if gesture.locationInView(UIApplication.sharedApplication().keyWindow).x >= view.frame.size.width - 20 || gesture.locationInView(UIApplication.sharedApplication().keyWindow).x <= 20 {

        }

    case .Ended:

        if (snap != nil) {
            animator.removeBehavior(snap)
        }

        snap = UISnapBehavior(item: activeView!, snapToPoint: view.center)
        snap.damping = 0.2
        animator.addBehavior(snap)

    default:
        break
    }
}
}

class SwipeableQuestion: UIView {

var questionLabel:UILabel = {
    var label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false
    label.numberOfLines = 0
    label.textAlignment = .Center
    label.font = UIFont(name: "HeliosCond", size: 22)
    return label
}()

lazy var topView:UIView = {
    var view = UIView()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.backgroundColor = UIColor().pinkColor()
    return view
}()

var questionNumLabel:UILabel = {
    var label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false
    label.textAlignment = .Center
    label.textColor = UIColor.whiteColor()
    label.font = UIFont(name: "HeliosCond", size: 16)
    return label
}()

var dummyView:UIView = {
    var view = UIView()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.backgroundColor = UIColor().pinkColor()
    return view
}()

override init(frame: CGRect) {
    super.init(frame: frame)

    addSubview(questionLabel)
    questionLabel.centerYAnchor.constraintEqualToAnchor(centerYAnchor).active = true
    questionLabel.centerXAnchor.constraintEqualToAnchor(centerXAnchor).active = true
    questionLabel.widthAnchor.constraintEqualToConstant(200).active = true

    addSubview(topView)
    topView.heightAnchor.constraintEqualToConstant(80).active = true
    topView.leadingAnchor.constraintEqualToAnchor(leadingAnchor).active = true
    topView.trailingAnchor.constraintEqualToAnchor(trailingAnchor).active = true
    topView.topAnchor.constraintEqualToAnchor(topAnchor).active = true

    topView.addSubview(questionNumLabel)
    questionNumLabel.centerXAnchor.constraintEqualToAnchor(topView.centerXAnchor).active = true
    questionNumLabel.centerYAnchor.constraintEqualToAnchor(topView.centerYAnchor).active = true

    topView.setRadius(6)

    addSubview(dummyView)
    dummyView.bottomAnchor.constraintEqualToAnchor(topView.bottomAnchor).active = true
    dummyView.leadingAnchor.constraintEqualToAnchor(leadingAnchor).active = true
    dummyView.trailingAnchor.constraintEqualToAnchor(trailingAnchor).active = true
    dummyView.heightAnchor.constraintEqualToConstant(15).active = true
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

}

如何避免眨眼和颤抖？