Animation triggered using a Button stops a repeatForever animation added onAppear

问题

I want to build a progress view that look like a circle that fills with water as the progress increase.

To do that, I've made a custom Shape that create the water and I added an Animation that repeat forever to a wave effect on that Shape. With that I wanted to add an animation while the progress increase to simulate that the water level increases.

The problem is that when I trigger this last animation, the one that it's added onAppear stop working. Is there a way to fix that so both animation are combining then the repeatForever one never stops ? Here is an example :

And here is the full code :

struct WaterWaveView: View {
    @State var progress: CGFloat = 0.1
    @State var phase: CGFloat = 0.5

    var body: some View {
        VStack {
            WaterWave(progress: self.progress, phase: self.phase)
                .fill(Color.blue)
                .clipShape(Circle())
                .frame(width: 250, height: 250)
                .onAppear {
                    withAnimation(Animation.linear(duration: 1)
                                    .repeatForever(autoreverses: false)) {
                        self.phase = .pi * 2
                    }
                }
            Button("Add") {
                withAnimation(.easeOut(duration: 1)) {
                    self.progress += 0.1
                }
            }
            Button("Reset") {
                self.progress = 0.0
            }
        }
    }
}

struct WaterWave: Shape {
    var progress: CGFloat
    let amplitude: CGFloat = 10
    let waveLength: CGFloat = 20
    var phase: CGFloat

    var animatableData: AnimatablePair<CGFloat, CGFloat> {
        get { AnimatablePair(phase, progress) }
        set {
            phase = newValue.first
            progress = newValue.second
        }
    }

    func path(in rect: CGRect) -> Path {
        var path = Path()

        let width = rect.width
        let height = rect.height
        let midWidth = width / 2
        let progressHeight = height * (1 - progress)

        path.move(to: CGPoint(x: 0, y: progressHeight))

        for x in stride(from: 0, to: width, by: 10) {
            let relativeX = x/waveLength
//            let normalizedLength = relativeX / midWidth

            let normalizedLength = (x - midWidth) / midWidth
            let y = progressHeight + sin(phase + relativeX) * amplitude * normalizedLength
            path.addLine(to: CGPoint(x: x, y: y))
        }

        path.addLine(to: CGPoint(x: width, y: progressHeight))
        path.addLine(to: CGPoint(x: width, y: height))
        path.addLine(to: CGPoint(x: 0, y: height))
        path.addLine(to: CGPoint(x: 0, y: progressHeight))

        return path
    }
}

回答1:

SwiftUI animations are not added(cumulated), at least for now (SwiftUI 2.0). So here is possible workaround.

Tested with Xcode 12 / iOS 14

struct WaterWaveView: View {
    @State var progress: CGFloat = 0.1
    @State var phase: CGFloat = 0.5

    var body: some View {
        VStack {
            WaterWave(progress: self.progress, phase: self.phase)
                .fill(Color.blue)
                .clipShape(Circle())
                .frame(width: 250, height: 250)
                .animation(phase == 0 ? .default : Animation.linear(duration: 1).repeatForever(autoreverses: false), value: phase)
                .animation(.easeOut(duration: 1), value: progress)
                .onAppear {
                            self.phase = .pi * 2
                }
            Button("Add") {
                    self.phase = 0
                    self.progress += 0.1
                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) {
                        self.phase = .pi * 2
                    }
            }
            Button("Reset") {
                self.progress = 0.0
            }
        }
    }
}

来源：https://stackoverflow.com/questions/64334667/animation-triggered-using-a-button-stops-a-repeatforever-animation-added-onappea