VolumeView.swift

//
//  ContentView.swift
//  Slider
//
//  Created by Ray Fix on 2/20/21.
//

import SwiftUI

struct VolumeView: View {

    @Binding var volume: Int?
    @State private var value: (CGFloat, enabled: Bool) = (50, true)

    var body: some View {
        VStack {
            if value.enabled {
                Text("\(Int(value.0))").font(.largeTitle)
            }
            else {
                Text("--").font(.largeTitle)
            }
            Slider(value: $value.0, in: 0...100)
                .disabled(!value.enabled)
            Toggle("Enabled", isOn: $value.enabled)
        }.padding()
        .onAppear() {
            value.enabled = volume != nil
            value.0 = CGFloat(volume ?? 19)
        }
        .onChange(of: value.0) { v in
            if value.enabled {
                volume = Int(v)
            }
            else {
                volume = nil
            }
        }
        .onChange(of: value.enabled) { e in
            volume = e ? Int(value.0) : nil
        }
    }
}

class Stereo: ObservableObject {
    @Published var volume: Int? = 22
}

struct ContentView: View {

    @StateObject private var stereo = Stereo()

    var body: some View {
        VStack {
            VolumeView(volume: $stereo.volume)
            if let v = stereo.volume {
                Text("Volume: \(v)")
            }
        }
    }
}

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