Swift 實現無止盡 360 度旋轉動畫的三個方法

開發 iOS App 時，我們有很多方法可以實現重覆 360 度旋轉的動畫。接下來我們分別看看以下三種實現的方法，SwiftUI 的 animation，UIKit 的 UIViewPropertyAnimator & UIKit 的 CABasicAnimation。

SwiftUI 的 animation

struct ContentView: View {
    
    @State private var degrees: Double = 0
    
    var body: some View {
        VStack {
            Image("peter")
                .rotationEffect(.degrees(degrees))
                .animation(Animation.linear(duration: 5).repeatForever(autoreverses: false))
            Text("我因為你而轉\n一圈一圈自轉")
                .font(.largeTitle)
}
        .onAppear {
            self.degrees = 360
        }
    }
}

UIKit 的 UIViewPropertyAnimator

class RotateImageView: UIImageView {
    
    
    func rotate() {
        let animator = UIViewPropertyAnimator(duration: 5, curve: .linear) {[weak self] in
            guard let self = self else { return }
            self.transform = CGAffineTransform(rotationAngle: .pi)
        }
        animator.addAnimations {[weak self] in
            guard let self = self else { return }
            self.transform = self.transform.rotated(by: .pi)
        }
        animator.addCompletion {[weak self] (_) in
            guard let self = self else { return }
            self.rotate()
        }
        animator.startAnimation()
    }
    
}

UIKit 的 CABasicAnimation

class RotateImageView: UIImageView {
    
    func rotate() {
        let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation")
        rotateAnimation.toValue = Double.pi * 2
        rotateAnimation.duration = 5
        rotateAnimation.repeatCount = .infinity
        layer.add(rotateAnimation, forKey: nil)
    }
    
}

若想要畫面一出現就呼叫 rotate 開始動畫，記得要在 viewWillAppear 或 viewDidAppear 再加入 CABasicAnimation，在 viewDidLoad 加入的話動畫將失效。

我因為你而轉 一圈一圈自轉