swift - 在 Swift 的 UIKit Dynamics 中，如何定义一个圆边界来包含一个 UIView？

Question

我研究了很多，但我在任何地方都能找到的唯一示例是为了定义 UIView 的边界，以便它们在对象的外部相互碰撞/反弹。

示例:一个球撞击另一个球，它们相互弹开。

但我想要做的是创建一个圆形 View 来包含其他 UIView，这样包含边界是一个圆，而不是默认的正方形。有办法实现吗？

Answer 1

是的，这完全可能。实现圆内碰撞的关键是

1. 将碰撞行为的边界设置为圆形路径(自定义UIBezierPath)和
2. 将动画师的 referenceView 设置为圆形 View 。

输出:

Storyboard设置:

下面是上述 Storyboard 的 View Controller 代码。魔法发生在 simulateGravityAndCollision 方法中:

Full Xcode project

class ViewController: UIViewController {
    
    @IBOutlet weak var redCircle: UIView!
    @IBOutlet weak var whiteSquare: UIView!
    
    var animator:UIDynamicAnimator!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.redCircle.setCornerRadius(self.redCircle.bounds.width / 2)
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.5) { [unowned self] in
            self.simulateGravityAndCollision()
        }
    }
    
    func simulateGravityAndCollision() {

        //The dynamic animation happens only within the reference view, i.e., our red circle view
        animator = UIDynamicAnimator.init(referenceView: self.redCircle)
        
        //Only the inside white square will be affected by gravity
        let gravityBehaviour = UIGravityBehavior.init(items: [self.whiteSquare])
        
        //We also apply collision only to the white square
        let collisionBehaviour = UICollisionBehavior.init(items:[self.whiteSquare])
        
        //This is where we create the circle boundary from the redCircle view's bounds
        collisionBehaviour.addBoundary(withIdentifier: "CircleBoundary" as NSCopying, for: UIBezierPath.init(ovalIn: self.redCircle.bounds))
        
        animator.addBehavior(gravityBehaviour)
        animator.addBehavior(collisionBehaviour)
    }
    
}

extension UIView {
    
    open override func awakeFromNib() {
        super.awakeFromNib()
        self.layer.allowsEdgeAntialiasing = true
    }
    
    func setCornerRadius(_ amount:CGFloat) {
        self.layer.cornerRadius = amount
        self.layer.masksToBounds = true
        self.clipsToBounds = true
    }
}