ios - 动画 UIView 到 "squiggle"到目的地的方式而不是直线前进

Question

我有这样的动画:

bubble.frame.origin = CGPoint(x: 75, y: -120)

UIView.animate(
    withDuration: 2.5,
    animations: {
        self.bubble.transform = CGAffineTransform(translationX: 0, y: self.view.frame.height * -1.3)
    }
)

但是，动画是直线进行的。我希望动画在到达目的地的途中来回移动一点。像一个泡沫。有什么想法吗？

Answer 1

如果您想沿路径设置动画，您可以使用 CAKeyframeAnimation。唯一的问题是您想要什么样的路径。阻尼正弦曲线可能就足够了:

func animate() {
    let box = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
    box.backgroundColor = .blue
    box.center = bubblePoint(1)
    view.addSubview(box)

    let animation = CAKeyframeAnimation(keyPath: "position")
    animation.path = bubblePath().cgPath
    animation.duration = 5
    box.layer.add(animation, forKey: nil)
}

在哪里

private func bubblePath() -> UIBezierPath {
    let path = UIBezierPath()
    path.move(to: bubblePoint(0))
    for value in 1...100 {
        path.addLine(to: bubblePoint(CGFloat(value) / 100))
    }

    return path
}

/// Point on curve at moment in time.
///
/// - Parameter time: A value between 0 and 1.
/// - Returns: The corresponding `CGPoint`.

private func bubblePoint(_ time: CGFloat) -> CGPoint {
    let startY = view.bounds.maxY - 100
    let endY = view.bounds.minY + 100
    let rangeX = min(30, view.bounds.width * 0.4)
    let midX = view.bounds.midX

    let y = startY + (endY - startY) * time
    let x = sin(time * 4 * .pi) * rangeX * (0.1 + time * 0.9) + midX
    let point = CGPoint(x: x, y: y)
    return point
}

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