AnimateForever.swift

import SwiftUI


struct AnimateForever: View {
    @State private var flag = false

    var body: some View {
        VStack {
            Rectangle()
                // on rectangle, foregroundColor() animate
                .foregroundColor(flag ? Color.green : Color.red)
                .frame(width: 150, height: 100)
            Text("Blah blah blah blah")
                // this animate!!
                .scaleEffect(flag ? 1 : 3)
                // ??? why the color is not animating?
                // it's a bug! see above rectangle works
                .foregroundColor(flag ? .green : .red)

            BoxIn()
                .foregroundColor(flag ? .green : .red)

            // works in sim or device, but in Xcode preview,
            if flag {
                Text("Blah blah blah blah")
                    .foregroundColor(.green)
            } else {
                Text("Blah blah blah blah")
                    .foregroundColor(.red)
            }
        }
        .onAppear { withAnimation(Animation.linear.repeatForever()) { flag.toggle() } }
    }
}


// Even when wrapping Text/Image in a view, foregroundColor() still do not animate
struct BoxIn: View {
    var body: some View {
        VStack {
            Text("Hello blah blah")

            Image(systemName: "folder.fill.badge.plus")
                .resizable()
                .aspectRatio(contentMode: .fit)
                .frame(width: 100)

            Circle()
                .frame(width: 150, height: 150)
        }
        .padding()
        .border(Color.yellow)
        .padding(.vertical, 50)
    }
}


struct AnimateForever_Previews: PreviewProvider {
    static var previews: some View {
        AnimateForever()
    }
}