ios - SwiftUI 动画 : How to stagger repeating animation with delay

Question

尝试在 SwiftUI 中实现以下动画并发现这是不可能的:



总结一下效果:一个重复的脉冲，以交错的延迟为每个片段设置动画。对于每个分割市场:

从不透明度 = 0.5 开始，比例 = 1

动画不透明度=1.0，比例=1.3

动画曲线开始快速，缓出时间更长

此外，每个“脉冲”之间都有延迟。

我使用 SwiftUI 能够做到的最接近的是使用 .repeatForever 连续重复的动画。修饰符。 (下面的代码。暂时忽略时间不匹配。)

如何在动画的每个循环之间添加延迟？

下面是我的代码的结果:

import SwiftUI

struct ArrowShape : Shape {

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

        path.move(to: CGPoint(x: 0, y: 0))
        path.addLine(to: CGPoint(x: rect.size.width, y: rect.size.height/2.0))
        path.addLine(to: CGPoint(x: 0, y: rect.size.height))

        return path
    }
}

struct Arrows: View {
    private let arrowCount = 3

    @State var scale:CGFloat = 1.0
    @State var fade:Double = 0.5

    var body: some View {

        ZStack {
            Color(red: 29.0/255.0, green: 161.0/255.0, blue: 224.0/255.0).edgesIgnoringSafeArea(.all)

            HStack{
                ForEach(0..<self.arrowCount) { i in
                    ArrowShape()
                        .stroke(style: StrokeStyle(lineWidth: CGFloat(10),
                                                  lineCap: .round,
                                                  lineJoin: .round ))
                        .foregroundColor(Color.white)
                        .aspectRatio(CGSize(width: 28, height: 70), contentMode: .fit)
                        .frame(maxWidth: 20)
                        .animation(nil)
                        .opacity(self.fade)
                        .scaleEffect(self.scale)
                        .animation(
                            Animation.easeOut(duration: 0.8)
                            .repeatForever(autoreverses: true)
                            .delay(0.2 * Double(i))
                        )
                }
            }

            .onAppear() {
                self.scale = 1.2
                self.fade = 1.0
            }
        }
    }
}



struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        Arrows()
    }
}

Answer 1

我认为你可以使用 Timer 和 DispatchQueue 来实现它，试试这个，看看它是否按你想要的方式工作

struct Arrows: View {
    private let arrowCount = 3

    let timer = Timer.publish(every: 2, on: .main, in: .common).autoconnect()

    @State var scale:CGFloat = 1.0
    @State var fade:Double = 0.5

    var body: some View {

        ZStack {
            Color(red: 29.0/255.0, green: 161.0/255.0, blue: 224.0/255.0).edgesIgnoringSafeArea(.all)

            HStack{
                ForEach(0..<self.arrowCount) { i in
                    ArrowShape()
                        .stroke(style: StrokeStyle(lineWidth: CGFloat(10),
                                                  lineCap: .round,
                                                  lineJoin: .round ))
                        .foregroundColor(Color.white)
                        .aspectRatio(CGSize(width: 28, height: 70), contentMode: .fit)
                        .frame(maxWidth: 20)
                        .animation(nil)
                        .opacity(self.fade)
                        .scaleEffect(self.scale)
                        .animation(
                            Animation.easeOut(duration: 0.5)
                            //.repeatForever(autoreverses: true)
                            .repeatCount(1, autoreverses: true)
                            .delay(0.2 * Double(i))
                        )
                }.onReceive(self.timer) { _ in
                     self.scale = self.scale > 1 ?  1 : 1.2
                     self.fade = self.fade > 0.5 ? 0.5 : 1.0
                     DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                                self.scale = 1
                                self.fade = 0.5
                            }
                    }
            }
        }
    }
}