围绕其中心旋转 UIImageView

Question

I am trying to rotate two UIImage its centre and I am having an issue (you can check on the gif image below), the rotation is fine, but the images are bobbing up and down, would anyone know what it can be?

Loader Animation

Loader Animation with background color

Here is the code that I am using to rotate the images

extension UIView {

private static let kRotationAnimationKey = "rotationAnimationKey"

func rotate(_ reversed: Bool = false, _ duration: Double = 1) {
    if layer.animation(forKey: UIView.kRotationAnimationKey) == nil {
        let rotationAnimation = CABasicAnimation(keyPath: "transform.rotation")
        rotationAnimation.fromValue = 0.0
        rotationAnimation.toValue = reversed ? -(Float.pi * 2.0) : Float.pi * 2.0
        rotationAnimation.duration = duration
        rotationAnimation.repeatCount = Float.infinity
        layer.add(rotationAnimation, forKey: UIView.kRotationAnimationKey)
    }
}

func stopRotating() {
    if layer.animation(forKey: UIView.kRotationAnimationKey) != nil {
        layer.removeAnimation(forKey: UIView.kRotationAnimationKey)
    }
}

Thank you all!

Answer 1

Created a circular view for this animation Using ShapeLayer and UIBezierPath you can use this class

public class CirclesView: UIView {

    //MARK:- properties
    private var numberOfCircles: Int = 2
    private var lineWidth: CGFloat = 8.0
    private var space = 20
    private var color : UIColor = .white
    private static let kRotationAnimationKey = "rotationanimationkey"

    private lazy var circularLayer: CAShapeLayer = {
        let shapeLayer = CAShapeLayer()
        shapeLayer.fillColor = UIColor.clear.cgColor
        shapeLayer.strokeColor = color.cgColor
        shapeLayer.lineCap = .round
        shapeLayer.lineWidth = self.lineWidth

        return shapeLayer
    }()

    //MARK:- inializer

    public init(_ circles: Int, circleWidth: CGFloat) {
        self.numberOfCircles = circles
        self.lineWidth = circleWidth
        super.init(frame: .zero)
        addSubLayer()
    }

    override init(frame: CGRect) {

        super.init(frame: frame)
        addSubLayer()
    }

    required init?(coder: NSCoder) {

        super.init(coder: coder)
        addSubLayer()
    }

    override public func layoutSubviews() {

        super.layoutSubviews()
        addCircles()

    }


}
private extension CirclesView {

    func addCircles() {
        circularLayer.bounds = self.bounds
        let bezierPath = UIBezierPath()

        let center = CGPoint(x: bounds.maxX / 2, y: bounds.maxY / 2)
        let maximumRadius =  min(bounds.maxX,bounds.maxY)/2 - (lineWidth / 2.0)
        var startAngle = CGFloat(60)
        var endAngle = CGFloat(130)


        for i in 1...numberOfCircles {

            let radius = maximumRadius - CGFloat(i * space)
            let  startX = center.x  + (radius) * CGFloat(cos(startAngle.deg2rad()))
            let  startY = center.y  + (radius) * CGFloat(sin(startAngle.deg2rad()))

            bezierPath.move(to: CGPoint(x: startX,y: startY))
            bezierPath.addArc(withCenter: center, radius: radius, startAngle: startAngle.deg2rad(), endAngle: endAngle.deg2rad(), clockwise: false)

            startAngle = startAngle - 10
            endAngle = endAngle + 50

        }

        circularLayer.path = bezierPath.cgPath
    }

    func addSubLayer() {
        self.backgroundColor = .clear
        layer.addSublayer(circularLayer)

    }


}

 //MARK:- Public Functions
public extension CirclesView {

    func startAnimation(_ reversed: Bool = false, _ duration: Double = 1) {

        let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation")
        rotateAnimation.fromValue = 0.0
        rotateAnimation.toValue = reversed ? -(Float.pi * 2.0) : Float.pi * 2.0
        rotateAnimation.duration = duration
        rotateAnimation.repeatCount = Float.infinity
        self.circularLayer.add(rotateAnimation, forKey: Self.kRotationAnimationKey)
    }

    func stopAnimation() {
        if let _ = circularLayer.animation(forKey: Self.kRotationAnimationKey)  {

            let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation")
            rotateAnimation.fromValue = circularLayer.presentation()?.value(forKeyPath: "transform.rotation")
            rotateAnimation.toValue = 0
            rotateAnimation.duration = 0.5
            rotateAnimation.repeatCount = 0
            rotateAnimation.isRemovedOnCompletion = true
            self.circularLayer.removeAnimation(forKey: Self.kRotationAnimationKey)
            self.circularLayer.add(rotateAnimation, forKey: Self.kRotationAnimationKey)
        }
    }

    func pauseLayer(){
        let pausedTime : CFTimeInterval = layer.convertTime(CACurrentMediaTime(), from: nil)
        circularLayer.speed = 0.0
        circularLayer.timeOffset = pausedTime
    }
}


 extension CGFloat {
    func deg2rad() -> CGFloat {
        return self * .pi / 180
    }
}

Github Project Link

Answer 2

Answer below:

It looks like your image asset isn't centred properly. Set the background colour of your image view so you can tell. The image view is probably rotating about its center, but the image content itself is probably off center. - Peter Parker

Basically your image of the rings does not have the rings smack in the middle. So you need to put that image into photoshop and export a new one such that the rings are smack in the middle. Peter Parker

Thanks Peter Parker