ZStack

is_this_a_bug.swift

import SwiftUI

struct ContentView1: View {
  @State var cond = false
  var body: some View {
    ZStack {
      Color.blue.opacity(cond ? 0.2 : 0.7)
      Test(cond: cond)
    }
    .onTapGesture {
      withAnimation(.easeInOut(duration: 1)) {
        cond.toggle()
      }
    }
  }
}

struct Test: View {
  var cond: Bool
  var body: some View {
    VStack {
      // animate properties of a single view
      // SwiftUI changes text immediately and animates the color & bounds
      Text(cond ? "One" : "Two")
        .padding(.leading, cond ? 10 : 20)
        .padding(.top, cond ? 20 : 10)
        .padding(.bottom, cond ? 20 : 10)
        .padding(.trailing, cond ? 10 : 20)
        .background(cond ? Color.green : Color.red)
      
      // swap views in or out of the view tree
      // SwiftUI adds the view immediately and animates the
      // swapped-out view's disappearance
      if cond {
        Text("One")
          .padding(.leading, 10)
          .padding(.top, 20)
          .padding(.bottom, 20)
          .padding(.trailing, 10)
          .background(Color.green)
      } else {
        Text("Two")
          .padding(.leading, 20)
          .padding(.top, 10)
          .padding(.bottom, 10)
          .padding(.trailing, 20)
          .background(Color.red)
      }
      
      // control view visibility through opacity
      // SwiftUI fades out one view as the other is fading in
      ZStack {
        Text("One")
          .padding(.leading, 10)
          .padding(.top, 20)
          .padding(.bottom, 20)
          .padding(.trailing, 10)
          .background(Color.green)
          .opacity(cond ? 1 : 0)
        Text("Two")
          .padding(.leading, 20)
          .padding(.top, 10)
          .padding(.bottom, 10)
          .padding(.trailing, 20)
          .background(Color.red)
          .opacity(cond ? 0 : 1)
      }
    }
  }
}

struct ContentView1_Previews: PreviewProvider {
  static var previews: some View {
    ContentView1()
  }
}