结合使用UIAttachmentBehavior和UICollisionBehavior

Question

使用UIKit动态，我想以某种方式组合UIAttachmentBehavior和UICollisionBehavior，这样用户就可以拖动视图(使用UIPanGestureRecognizer)，但不会离开某个区域。

当用户/UIView与碰撞行为的边界发生冲突时，问题就出现了，因为此时不可能进行垂直移动。

也就是说，当与边界区域的左侧碰撞时，一个人被“卡住”在那里，不能向上或向下移动，恰到好处。将UIView拖回到原来的路径上是可行的。

我们非常感谢UIDynamicItemBehavior解决这个问题的任何帮助(尝试过弹性、摩擦力和阻力，但都无济于事)。

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Answer 1

我认为您以错误的方式实现了UIPanGestureRecognizer。尝试下面的示例。只需创建一个新项目并将此代码粘贴到您的ViewController中。如果您需要减小可拖动区域，可以使用dragView函数。

import UIKit

class ViewController: UIViewController, UICollisionBehaviorDelegate {

    var collision: UICollisionBehavior!
    var animator: UIDynamicAnimator!

    override func viewDidLoad() {
        super.viewDidLoad()

        let container = UIView(frame: CGRect(x: 30, y: 60, width: 300, height: 500))
        self.view.addSubview(container)
        container.backgroundColor = .gray

        self.animator = UIDynamicAnimator(referenceView: container);
        //self.animator.setValue(true, forKey: "debugEnabled")

        let greenBox = UIView(frame: CGRect(x: 60, y: 240, width: 50, height: 50))
        greenBox.backgroundColor = .green
        container.addSubview(greenBox)

        let blueBox = UIView(frame: CGRect(x: 10, y: 10, width: 50, height: 50))
        blueBox.backgroundColor = .blue
        container.addSubview(blueBox)

        let redBox = UIView(frame: CGRect(x: 200, y: 300, width: 50, height: 50))
        redBox.backgroundColor = .red
        container.addSubview(redBox)

        self.collision = UICollisionBehavior(items: [greenBox, blueBox, redBox])
        self.collision.translatesReferenceBoundsIntoBoundary = true
        self.collision.collisionMode = .everything
        self.animator.addBehavior(self.collision)
        self.collision.collisionDelegate = self


        let c = UIDynamicItemBehavior(items: [redBox])
        c.density = 10000
        self.animator.addBehavior(c)

        let noRotation = UIDynamicItemBehavior(items: [greenBox, blueBox])
        noRotation.allowsRotation = false
        self.animator.addBehavior(noRotation)

        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(self.dragView(_:)))
        greenBox.isUserInteractionEnabled = true
        greenBox.addGestureRecognizer(panGesture)

        let panGesture2 = UIPanGestureRecognizer(target: self, action: #selector(self.dragView(_:)))
        blueBox.isUserInteractionEnabled = true
        blueBox.addGestureRecognizer(panGesture2)

    }


    @objc func dragView(_ sender:UIPanGestureRecognizer){

        if let viewDrag = sender.view {
            self.view.bringSubview(toFront: viewDrag)
            let translation = sender.translation(in: self.view)
            viewDrag.center = CGPoint(x: viewDrag.center.x + translation.x, y: viewDrag.center.y + translation.y)
            sender.setTranslation(CGPoint.zero, in: self.view)
            animator.updateItem(usingCurrentState: viewDrag)
        }
    }

}