How can I use a common variable in a Tab VIew? - swiftui

Question

I'm currently developing an application using SwiftUI.
This app has 3 structs
①ContentView
②FirstView
③SecondView
These 3 structs do page transition in Tab View.
And this app has a common variable type of Bool using ObservableObject annotation.
I want to change to appear and disappear Text View in the FirstView and the SecondView depends on the condition of the variable, but the FirstView doesn't change a view as I expected...
How can I solve this situation?
Here are the codes:
ContentView.swift
import SwiftUI
struct ContentView: View {
var body: some View {
TabView {
FirstView()
.tabItem {
Text("First")
}.tag(1)
SecondView()
.tabItem {
Text("Second")
}.tag(2)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
FirstView.swift
import SwiftUI
struct FirstView: View {
#ObservedObject var firstCheck: ViewModel = ViewModel()
var body: some View {
VStack{
if firstCheck.check == true{
Text("checked")
}
}
}
}
struct FirstView_Previews: PreviewProvider {
static var previews: some View {
FirstView()
}
}
SecondView.swift
import SwiftUI
struct SecondView: View {
#ObservedObject var secondCheck = ViewModel()
var body: some View {
VStack{
Toggle(
isOn: $secondCheck.check
){
Text("change")
}
if self.secondCheck.check == true{
Text("checked")
}
}
}
}
struct SecondView_Previews: PreviewProvider {
static var previews: some View {
SecondView()
}
}
ViewModel.swift
import Foundation
final class ViewModel: ObservableObject {
#Published var check: Bool = false
}
Xcode: Version 11.7

Answer 1

Keep object in one place, can be parent view
struct ContentView: View {
#ObservedObject var viewModel = ViewModel()
// #StateObject var viewModel = ViewModel() // SwiftUI 2.0
var body: some View {
TabView {
// .. other code here
}
.environmentObject(viewModel) // << inject here
}
}
and then use in both views like (for second the same)
struct FirstView: View {
#EnvironmentObject var firstCheck: ViewModel // declare only
// will be injected by type
var body: some View {
VStack{
if firstCheck.check == true{
Text("checked")
}
}
}
}