Question

我正在使用CAKeyframeAnimation实现一个财富之轮，并在动画停止后尝试读取结果。但在这里，我没有得到确定性的结果。动画停止后是否无法读取旋转？

这是我的动画代码：

let anim = CAKeyframeAnimation(keyPath: "transform.rotation.z")
        anim.duration = max(strength / 2, 1.0)
        anim.isCumulative = true
        anim.values = [NSNumber(value: Float(p)), Float(circleRotationOffset)]
        anim.keyTimes = [NSNumber(value: Float(0)),NSNumber(value: Float(1.0))]
        anim.timingFunctions = [CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseOut)]
        anim.isRemovedOnCompletion = false
        anim.fillMode = kCAFillModeForwards
        anim.delegate = self
        wheelImage.layer.removeAllAnimations()
        wheelImage.layer.add(anim, forKey: "rotate")

在这里我如何阅读轮换：

func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {

        readImageOrientation()
    }


    func readImageOrientation(){

        let radians:Double = atan2( Double(wheelImage.transform.b), Double(wheelImage.transform.a))
        let degrees:CGFloat = CGFloat(radians) * (CGFloat(180) / CGFloat(M_PI))

        sectionForDegrees(degree: degrees)
    }

为了完整起见，我完整的课程。

class WOFView: UIView, CAAnimationDelegate {

@IBOutlet weak var wheelImage: UIImageView!
private var history = [Dictionary<String, Any>]()
private var rotation: CGFloat = 0
private var startAngle: CGFloat = 0
private var circleRotationOffset: CGFloat = 0


override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)

    if let touchPoint = touches.first?.location(in: self){

        if startAngle == 0{
            startAngle = atan2(self.frame.width - touchPoint.y, self.frame.height - touchPoint.x)
        }
        rotation = startAngle
        if !touch(touches.first!, isInLeftHalfOf: wheelImage) {
            rotation = -rotation
        }
        history.removeAll()
    }
}


override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)

    guard let touchPoint = touches.first?.location(in: self) else {
        return
    }

    let dic = ["time" : NSNumber(value: CFAbsoluteTimeGetCurrent()),
               "point": NSValue(cgPoint: touchPoint),
               "rotation": NSNumber(value: Float(circleRotationOffset + rotation))]

    history.insert(dic, at: 0)
    if history.count == 3{
        history.removeLast()
    }

    rotation = atan2(self.frame.width - touchPoint.y, self.frame.height - touchPoint.x) - startAngle
    if !touch(touches.first!, isInLeftHalfOf: wheelImage) {
        rotation = -rotation
    }
    wheelImage.transform = CGAffineTransform(rotationAngle: circleRotationOffset + rotation)
    print("offset: \(circleRotationOffset)")
    readImageOrientation()
}


override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesEnded(touches, with: event)

    guard let touchPoint = touches.first?.location(in: self) else {
        return
    }

    guard let lastObject = history.last else{
        return
    }

    guard let pointValue = lastObject["point"] as? CGPoint else{
        return
    }

    guard let timeValue = lastObject["time"] as? NSNumber else {
        return
    }

    guard let rotationValue = lastObject["rotation"] as? NSNumber else {
        return
    }

    let timeDif = CFAbsoluteTimeGetCurrent() - (timeValue.doubleValue)
    circleRotationOffset = circleRotationOffset + rotation
    let lastRotation = rotationValue.floatValue

    let dist = sqrt(((pointValue.x - touchPoint.x) * (pointValue.x - touchPoint.x)) +
        ((pointValue.y - touchPoint.y) * (pointValue.y - touchPoint.y)))

    let strength = max(Double(min(1.0, dist / 80.0)) * (timeDif / 0.25) * M_PI * 2, 0.3) * 30

    let p = circleRotationOffset
    let dif = circleRotationOffset - CGFloat(lastRotation)
    var inc = dif > 0

    if dif > 3 || dif < -3{
        inc = !inc
    }


    if (inc){
        circleRotationOffset += CGFloat(strength)
    }else{
        circleRotationOffset -= CGFloat(strength)
    }

    let anim = CAKeyframeAnimation(keyPath: "transform.rotation.z")
    anim.duration = max(strength / 2, 1.0)
    anim.isCumulative = true
    anim.values = [NSNumber(value: Float(p)), Float(circleRotationOffset)]
    anim.keyTimes = [NSNumber(value: Float(0)),NSNumber(value: Float(1.0))]
    anim.timingFunctions = [CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseOut)]
    anim.isRemovedOnCompletion = false
    anim.fillMode = kCAFillModeForwards
    anim.delegate = self
    wheelImage.layer.removeAllAnimations()
    wheelImage.layer.add(anim, forKey: "rotate")
}


func touch(_ touch:UITouch, isInLeftHalfOf view: UIView) -> Bool {
    let positionInView = touch.location(in: view)
    return positionInView.x < view.frame.midX
}

func touch(_ touch:UITouch, isInUpperHalfOf view: UIView) -> Bool {
    let positionInView = touch.location(in: view)
    return positionInView.y < view.frame.midY
}


func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {

    readImageOrientation()
}


func readImageOrientation(){

    let radians:Double = acos(Double(wheelImage.transform.a))
    let degrees:CGFloat = CGFloat(radians) * (CGFloat(180) / CGFloat(M_PI))

    sectionForDegrees(degree: degrees)
}

func sectionForDegrees(degree: CGFloat){

    var result = "not defined"

    switch degree{
    case 0 ... 90:
        result = "3 \(degree)"
    case 90.1...180:
        result = "2 \(degree)"
    case 181.1...270:
        result = "1 \(degree)"
    case 270.1...360:
        result = "4 \(degree)"

    default:
        result = "not defined: \(degree)"
    }

    print(result)
}

}

Answer 1

根据this Objective-C answer，至少有四种方法可以获得轮换：

let view = UIImageView()
view.transform = CGAffineTransform(rotationAngle: 0.02);

let x = view.value(forKeyPath: "layer.transform.rotation.z")
let a = acos(view.transform.a)
let b = asin(view.transform.b)
let c = atan2(view.transform.b, view.transform.a)

print(a)
print(b)
print(c)
print(x!)

打印：

0.0200000000000011
0.02
0.02
0.02

Answer 2

原始答案（关于转换的一般想法）

我认为你应该使用acos()代替atan2()，基于三维旋转矩阵的外观：

在这个Rz矩阵中，我们可以看到transform.a和transform.b将作为余弦θ给出。参考CGAffineTransform documentation：

如果不进行测试，我非常确定一个简单的acos(Double(wheelImage.transform.a))足以让你进行θ旋转。编辑：这是一个糟糕的建议，用atan2替换acos意味着您必须检查您的答案是正值还是负余弦值，并且完全没有意义。另一件需要记住的事情是，如果对轮子应用任何缩放，变换也会发生变化。

如果我错了，您可以随时使用strength值来计算允许滚轮旋转多长时间并从中找到角度。这将需要您了解kCAMediaTimingFunctionEaseOut如何正确工作，所以我建议您更改动画以首先计算角度（您保存为参数）然后将其直接应用于{{1}而不是将持续时间用作决定性因素。

更新答案

看到完整的代码后，我发现你只解释了错误的角度，这里是对你的layer.transform函数的重写，它将给出正确的部分：

sectionForDegrees

用动画旋转图像，然后读取旋转

2 个答案:

原始答案（关于转换的一般想法）

更新答案