SwiftUI animation: How to stagger repeating animation with delay

Question

Trying to implement the following animation in SwiftUI and finding it quite impossible:

To summarize the effect: A repeating pulse, animating each segment with a staggered delay. For each segment:

• Starting at opacity=0.5, scale = 1
• Animate to opacity=1.0, scale = 1.3
• The animation curve is starts quickly with a longer ease-out

In addition, there is delay between each 'pulse'.

The closest I've been able to get to this with SwiftUI is a continuously repeating animation using the .repeatForever modifier. (Code below. Ignore the mismatch in timing for now.)

How can I Add a delay between each loop of the animation?

Here is the result of my code below:

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

I think you can implement it using Timer and DispatchQueue, try this and see it's working as you want or no

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
                            }
                    }
            }
        }
    }
}