Swift：使用动画创建圆

我是新来的

我试图通过UIDynamicMator创建落圆对象。然而，它看起来不够真实

1） 每个圆形物体之间都有“空间”。不确定是否正确创建了圆对象

2） 顶部的某些圆形对象似乎卡在顶部，而不是掉落

有人能帮我吗？非常感谢

有关更清晰的图片，请参阅此链接以获取图像：

var circle : UIView?
var animator:UIDynamicAnimator? = nil;
let gravity = UIGravityBehavior()
let collider = UICollisionBehavior()
let bounce = UIDynamicItemBehavior()

func addcircle(location: CGRect) {
    let newCircle = UIView(frame: location)
    newCircle.backgroundColor = UIColor.whiteColor()
    newCircle.layer.cornerRadius = newBox.frame.width / 2
    newCircle.clipsToBounds = true

    view.insertSubview(newBox, atIndex: 0)
    circle = newCircle
}

func animateCircle() {
    animator = UIDynamicAnimator(referenceView:self.view);
    animator?.addBehavior(collider)

    gravity.addItem(circle!);
    gravity.gravityDirection = CGVectorMake(0, 0.5)
    animator?.addBehavior(gravity);

    collider.addItem(circle!)
    collider.translatesReferenceBoundsIntoBoundary = true
    animator?.addBehavior(collider)

    bounce.addItem(circle!)
    bounce.elasticity = 0.5
    animator?.addBehavior(bounce)

}