[Swift] 刻々と変わるオブジェクトの値を表示

ValueMaker.swift

import Foundation

class ValueMaker: ObservableObject {
    
    @Published var value: Double = 0.0
    private var timer = Timer()
    
    func start() {
        timer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true) {
            _ in
            self.value = Double.random(in: 0 ... 1)
        }
    }
}

ContentView.swift

struct ContentView: View {
    @ObservedObject var maker = ValueMaker()

    var body: some View {
        VStack (alignment: .leading, spacing: 10){
            Text("\(maker.value)")
                .font(.largeTitle)
                .foregroundColor((maker.value > 0.8) ? .white : .gray)
                .background((maker.value > 0.8) ? Color.red : Color.white)
            ZStack {
                Rectangle().stroke(.gray)
                Rectangle()
                    .foregroundColor(.green)
                    .scaleEffect(x:maker.value, y:1.0, anchor: .leading)
            }
        }
        .frame(width: 200, height: 80)
        .onAppear(perform: {
            maker.start()
        })
    }
}

Timer.scheduledTimerとして、Double.random(in: 0 … 1)で値を出力する
@ObservedObject var maker = ValueMaker()　でValueMakerを呼び出している