CAShapeLayer circle strokeEnd 没有连接到开始

Question

我正在创建一个类似于右侧 here Android material 设计加载指示器的圆圈，但该圆圈并未自行完成。

class ViewController: UIViewController {

    var baseLayer = CAShapeLayer()

    override func viewDidLoad() {
        super.viewDidLoad()
        setUp()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        animate()
    }

    private func setUp() {
        view.layer.addSublayer(baseLayer)
        let basePath = UIBezierPath(arcCenter: view.center,
                                    radius: 100,
                                    startAngle: CGFloat.pi / 2,
                                    endAngle: 2 * CGFloat.pi,
                                    clockwise: true).cgPath
        baseLayer.strokeColor = UIColor.gray.cgColor
        baseLayer.path = basePath
        baseLayer.fillColor = UIColor.clear.cgColor
        baseLayer.lineWidth = 2
        baseLayer.position = view.center
        baseLayer.strokeEnd = 0
    }

    private func animate() {
        CATransaction.begin()
        let strokeEndAnimation = CABasicAnimation(keyPath: "strokeEnd")
        strokeEndAnimation.toValue = 1
        strokeEndAnimation.fillMode = .forwards
        strokeEndAnimation.isRemovedOnCompletion = false
        strokeEndAnimation.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)

        let rotationAnimation = CABasicAnimation(keyPath: "transform.rotation")
        rotationAnimation.toValue = CGFloat.pi
        rotationAnimation.fillMode = .forwards
        rotationAnimation.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut)
        rotationAnimation.isRemovedOnCompletion = false

        let group = CAAnimationGroup()
        group.duration = 1.5
        group.repeatCount = 0
        group.fillMode = .forwards
        group.isRemovedOnCompletion = false
        group.animations = [strokeEndAnimation, rotationAnimation]

        baseLayer.add(group, forKey: "animations")
        CATransaction.commit()
    }
}

下图显示了我在说什么。它正确地停在 3*pi/2 但我相信 strokeEnd 错误地停在 pi。我尝试了 strokeEnd 和转换动画的各种不同配置，但似乎没有任何效果。修改 strokeEnd toValue 动画不会改变任何东西。

Answer 1

圆周率是圆的二分之一。如果您删除旋转，并将其用作您的 basePath:

    basePath = UIBezierPath(arcCenter: view.center,
                            radius: 100,
                            startAngle: 0,
                            endAngle: 1.0 * CGFloat.pi,
                            clockwise: true).cgPath

该行将从 3:00 开始并转到 9:00

如果你从二分之一开始：

    basePath = UIBezierPath(arcCenter: view.center,
                            radius: 100,
                            startAngle: CGFloat.pi / 2,
                            endAngle: 1.0 * CGFloat.pi,
                            clockwise: true).cgPath

你的行从 6:00 到 9:00

在endAngle上加一个半圆周角：

    basePath = UIBezierPath(arcCenter: view.center,
                            radius: 100,
                            startAngle: CGFloat.pi / 2,
                            endAngle: 1.5 * CGFloat.pi,
                            clockwise: true).cgPath

然后你得到 6:00 到 12:00，这几乎你想要的。

现在你添加 PI 的旋转（记住，那是一个完整圆的二分之一）：

你在 12:00 到 6:00。

为了达到 12:00，必须添加另一个 PI

    var basePath = UIBezierPath(arcCenter: view.center,
                                radius: 100,
                                startAngle: CGFloat.pi / 2,
                                endAngle: 2.5 * CGFloat.pi,
                                clockwise: true).cgPath

CAShapeLayer circle strokeEnd 没有连接到开始

CAShapeLayer circle strokeEnd not connecting to start

caanimation

ios

swift