ios - UIPanGestureRecognizer 有时不会进入最终状态

Question

我正在开发一个类似于 Tinder 中的卡片 View 。当卡片X原点大于我声明的值时，它会移出屏幕。否则，它会再次粘在中心。我正在 UIPanGestureRecognizer 函数中执行所有这些操作。我可以在 Change 状态下移动 View 。但是，它有时不会进入最终状态，因此卡片既不会移出屏幕也不会再次粘在中心。它只是停留在一些奇怪的地方。

所以我的问题是卡片应该像下面的屏幕截图一样离开屏幕或粘在中间。

我尝试了下面帖子中的解决方案，但没有任何效果:

UIPanGestureRecognizer not calling End state

UIPanGestureRecognizer does not switch to state "End" or "Cancel" if user panned x and y in negative direction

/// This method handles the swiping gesture on each card and shows the appropriate emoji based on the card's center.
@objc func handleCardPan(sender: UIPanGestureRecognizer) {

    // Ensure it's a horizontal drag
    let velocity = sender.velocity(in: self.view)
    if abs(velocity.y) > abs(velocity.x) {
        return
    }

    // if we're in the process of hiding a card, don't let the user interace with the cards yet
    if cardIsHiding { return }
    // change this to your discretion - it represents how far the user must pan up or down to change the option
    // distance user must pan right or left to trigger an option
    let requiredOffsetFromCenter: CGFloat = 80

    let panLocationInView = sender.location(in: view)
    let panLocationInCard = sender.location(in: cards[0])

    switch sender.state {
    case .began:
        dynamicAnimator.removeAllBehaviors()
        let offset = UIOffsetMake(cards[0].bounds.midX, panLocationInCard.y)
        // card is attached to center
        cardAttachmentBehavior = UIAttachmentBehavior(item: cards[0], offsetFromCenter: offset, attachedToAnchor: panLocationInView)
        //dynamicAnimator.addBehavior(cardAttachmentBehavior)
        let translation = sender.translation(in: self.view)
        print(sender.view!.center.x)
        sender.view!.center = CGPoint(x: sender.view!.center.x + translation.x, y: sender.view!.center.y)

        sender.setTranslation(CGPoint(x: 0, y: 0), in: self.view)
    case .changed:
        //cardAttachmentBehavior.anchorPoint = panLocationInView
        let translation = sender.translation(in: self.view)
        print(sender.view!.center.x)
        sender.view!.center = CGPoint(x: sender.view!.center.x + translation.x, y: sender.view!.center.y)
        sender.setTranslation(CGPoint(x: 0, y: 0), in: self.view)

    case .ended:

        dynamicAnimator.removeAllBehaviors()

        if !(cards[0].center.x > (self.view.center.x + requiredOffsetFromCenter) || cards[0].center.x < (self.view.center.x - requiredOffsetFromCenter)) {
            // snap to center
            let snapBehavior = UISnapBehavior(item: cards[0], snapTo: CGPoint(x: self.view.frame.midX, y: self.view.frame.midY + 23))
            dynamicAnimator.addBehavior(snapBehavior)
        } else {
            let velocity = sender.velocity(in: self.view)
            let pushBehavior = UIPushBehavior(items: [cards[0]], mode: .instantaneous)
            pushBehavior.pushDirection = CGVector(dx: velocity.x/10, dy: velocity.y/10)
            pushBehavior.magnitude = 175
            dynamicAnimator.addBehavior(pushBehavior)

            // spin after throwing
            var angular = CGFloat.pi / 2 // angular velocity of spin
            let currentAngle: Double = atan2(Double(cards[0].transform.b), Double(cards[0].transform.a))

            if currentAngle > 0 {
                angular = angular * 1
            } else {
                angular = angular * -1
            }
            let itemBehavior = UIDynamicItemBehavior(items: [cards[0]])
            itemBehavior.friction = 0.2
            itemBehavior.allowsRotation = true
            itemBehavior.addAngularVelocity(CGFloat(angular), for: cards[0])
            dynamicAnimator.addBehavior(itemBehavior)

            showNextCard()
            hideFrontCard()

        }
    default:
        break
    }
}

Answer 1

我正在检查是否水平滑动:

let velocity = sender.velocity(in: self.view)
if abs(velocity.y) > abs(velocity.x) {
    return
}

由于某种原因，当我水平滑动时它正在返回。当我评论这段代码时，一切都开始工作了:)