Why does `Color.` used as aSwiftUI ZStack background not update on TabView on a real device?

问题

This code appears to work very well on the canvas preview, but on my real device, sometimes the background color does not update. When switching tabs, the color from the former view remains although the rest of the view is fine. What gives?

Here is the main tab view:

import SwiftUI

struct ContentView: View {

    @EnvironmentObject var isModalVisible: CustomModal
    @ObservedObject var modal = CustomModal()

    var body: some View {

        ZStack {
            TabView {
                ZStack {
                Color.pink.opacity(0.2)
                        Button(action: {
                            withAnimation{
                                self.isModalVisible.isModalVisible.toggle()
                                self.modal.currentModal = VisibleModal.circle
                            }
                        }) {
                            Text("Circle").font(.headline)
                        }
                        .frame(width: 270, height: 64)
                        .background(Color.pink.opacity(0.5)).foregroundColor(.white)
                        .cornerRadius(12)
                }
                   .tabItem{
                       VStack{
                       Image(systemName: "1.square.fill")
                       Text("One")
                       }
                    }.tag(1)
                   ZStack {
                   Color.blue.opacity(0.2)
                       Button(action: {
                        self.isModalVisible.isModalVisible.toggle()
                        self.modal.currentModal = VisibleModal.squircle
                       }) {
                           Text("Squircle").font(.headline)
                       }
                       .frame(width: 270, height: 64)
                       .background(Color.blue.opacity(0.5)).foregroundColor(.white)
                       .cornerRadius(12)
                       }
                   .tabItem{
                          VStack{
                          Image(systemName: "2.square.fill")
                          Text("Two")
                          }
                       }.tag(2)
               }.accentColor(.purple)
            if self.isModalVisible.isModalVisible {
                VStack {
                    containedView().onAppear().transition(AnyTransition.scale.combined(with: .opacity).animation(.easeInOut(duration: 3.75)))

                }
            }
        }
    }

    func containedView() -> AnyView {
        switch modal.currentModal {
           case .circle: return AnyView(CircleView())
           case .squircle: return AnyView(SquircleView())
           case .none: return AnyView(Text(""))
        }
    }
}

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

And here is the other file with the subview modals:

import SwiftUI

class CustomModal: ObservableObject {
    @Published var isModalVisible = false
    @Published var currentModal: VisibleModal = .none
}

enum VisibleModal {
    case circle, squircle, none
}

struct CircleView: View {
    @EnvironmentObject var env: CustomModal

    var body: some View {
        ZStack {
            Color.pink.blur(radius: 0.4)
            Circle().fill()
            .frame(width: 300)
                .foregroundColor(Color.white.opacity(0.75))
            dismissButton()
        }.edgesIgnoringSafeArea(.all)
            .onAppear()
                .transition(AnyTransition.scale.combined(with: .opacity).animation(.easeInOut(duration: 3.75)))
    }
}

struct SquircleView: View {
    var body: some View {
        ZStack{
            Color.green.blur(radius: 0.4)
            RoundedRectangle(cornerRadius: 78, style: .continuous)
                .frame(width: 300, height: 300).foregroundColor(Color.white.opacity(0.75))
            dismissButton()
        }.edgesIgnoringSafeArea(.all)
    }
}

struct dismissButton: View {

    @EnvironmentObject var env: CustomModal

    var body: some View {
        VStack{
            Spacer()
            Button(action: {
                self.env.isModalVisible.toggle()
                print("TAPPED")
            }) {
                Text("Dismiss").font(.headline)
            }
            .frame(width: 270, height: 64)
            .background(Color.white.opacity(0.35)).foregroundColor(.white)
            .cornerRadius(12)
            .padding(.bottom, 44)
        }
    }
}

struct SecondFile_Previews: PreviewProvider {
    static var previews: some View {
        /*@START_MENU_TOKEN@*/Text("Hello, World!")/*@END_MENU_TOKEN@*/
    }
}

My goal here is to use an enum to select a full screen modal view from the main view.

I actually have a secondary question: how would one get animations to work with this? They don't seem to.

来源：https://stackoverflow.com/questions/61009837/why-does-color-used-as-aswiftui-zstack-background-not-update-on-tabview-on-a