实现一个扫描二维码的动画效果，然而SwiftUI中没有提供CABasicAnimation 动画方法，该如何实现这种效果？先弄清楚什么关键帧动画，简单的说就是指视图从起点至终点的状态变化，可以是形状、位置、透明度等等

本文提供了一种方法Timer + offset + animation+@State，来实现位移变化

struct HomePage: View {
    @State var openScanQR = false
    @State var scanResult:String = ""
    @State var isAnimated = false
    @State var timer = Timer.publish(every: 3, on: .main, in: .common).autoconnect()
    var body: some View {
        
        VStack{
        
        }
        .ignoresSafeArea(edges: .top)
        .fullScreenCover(isPresented: $openScanQR, content: {
            ScannerView(result: $scanResult)
                .overlay(ZStack{
                    Color.black.opacity(0.5)
                    Image("scan_round")
                        .resizable()
                        .renderingMode(.template)
                        .aspectRatio(contentMode: .fill)
                        .foregroundColor(.blue)
                        .frame(height: UIScreen.main.bounds.width - 80)
                        .padding(.horizontal, 40)
                    Image("scan_line")
                        .resizable()
                        .renderingMode(.template)
                        .aspectRatio(contentMode: .fill)
                        .foregroundColor(.blue)
                        .frame(height: 2)
                        .padding(.horizontal, 40)
                        .offset(y: !isAnimated ? -(UIScreen.main.bounds.width - 80)/2:  (UIScreen.main.bounds.width - 80)/2)
                        .animation(.easeOut(duration: 3), value: isAnimated)
                })
        
                .edgesIgnoringSafeArea(.all)
        })
        .onReceive(timer, perform: { _ in
            withAnimation {
                isAnimated.toggle()
            }
        })
        .background(Color.background_color)
        .edgesIgnoringSafeArea(.top)

    }
}