与其说这是一个 Swift 问题,不如说它是一个数学问题。关于数学部分,您需要检查计算旋转的方法的结果是否为负并返回绝对值,否则返回 360 减去角度:
func angle(from location: CGPoint) -> CGFloat {
let deltaY = location.y - view.center.y
let deltaX = location.x - view.center.x
let angle = atan2(deltaY, deltaX) * 180 / .pi
return angle < 0 ? abs(angle) : 360 - angle
}
关于动画部分,我建议使用CABasicAnimation,将isRemovedOnCompletion设置为false,将fillMode设置为kCAFillModeForwards,将timingFunction设置为线性。其他重要的设置是 from 和 to,您应该对它们使用相同的值,持续时间为 0:
fileprivate let rotateAnimation = CABasicAnimation()
func rotate(to: CGFloat, duration: Double = 0) {
rotateAnimation.fromValue = to
rotateAnimation.toValue = to
rotateAnimation.duration = duration
rotateAnimation.repeatCount = 0
rotateAnimation.isRemovedOnCompletion = false
rotateAnimation.fillMode = kCAFillModeForwards
rotateAnimation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear)
imageView.layer.add(rotateAnimation, forKey: "transform.rotation.z")
}
要将度数转换为弧度,您可以使用此扩展answer:
extension FloatingPoint {
var degreesToRadians: Self { return self * .pi / 180 }
var radiansToDegrees: Self { return self * 180 / .pi }
}
要保留启动之间的轮换,您可以向 UserDefault 添加计算属性:
extension UserDefaults {
/// rotation persistant computed property
var rotation: CGFloat {
get {
return CGFloat(double(forKey: "rotation"))
}
set {
set(Double(newValue), forKey: "rotation")
}
}
}
关于手势识别器,您需要切换手势状态以检测其开始、变化和结束并采取相应的操作:
fileprivate var rotation: CGFloat = UserDefaults.standard.rotation
fileprivate var startRotationAngle: CGFloat = 0
@objc func pan(_ gesture: UIPanGestureRecognizer) {
let location = gesture.location(in: view)
let gestureRotation = CGFloat(angle(from: location)) - startRotationAngle
switch gesture.state {
case .began:
// set the start angle of rotation
startRotationAngle = angle(from: location)
case .changed:
rotate(to: rotation - gestureRotation.degreesToRadians)
case .ended:
// update the amount of rotation
rotation -= gestureRotation.degreesToRadians
default :
break
}
// save the final position of the rotation to defaults
UserDefaults.standard.rotation = rotation
}
并将手势识别器添加到您的视图中:
class ViewController: UIViewController, UIGestureRecognizerDelegate {
@IBOutlet weak var imageView: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
let address = "https://i.stack.imgur.com/xnZXF.jpg"
let url = URL(string: address)!
rotate(to: rotation)
URLSession.shared.dataTask(with: url) { data, response, error in
guard let data = data else { return }
DispatchQueue.main.async {
self.imageView.image = UIImage(data: data)
let pan = UIPanGestureRecognizer(target: self, action:#selector(self.pan))
pan.minimumNumberOfTouches = 1
pan.maximumNumberOfTouches = 1
pan.delegate = self
self.view.addGestureRecognizer(pan)
}
}.resume()
}
// rest of the view controller code
}
示例项目