@EnvironmentObject — 概要、動作原理、使用方法

struct MiddleView: View {
    @ObservedObject var settings: UserSettings  // only needed to pass down

    var body: some View {
        ChildView(settings: settings)
    }
}

struct MiddleView: View {
    var body: some View {
        ChildView()
    }
}

struct ChildView: View {
    @EnvironmentObject var settings: UserSettings

    var body: some View {
        Text(settings.username)
    }
}

import SwiftUI
import Combine

class AuthManager: ObservableObject {
    @Published var isLoggedIn = false
    @Published var username: String = ""

    func login(user: String) {
        username = user
        isLoggedIn = true
    }

    func logout() {
        username = ""
        isLoggedIn = false
    }
}

@main
struct MyApp: App {
    @StateObject private var authManager = AuthManager()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(authManager)
        }
    }
}

struct ProfileView: View {
    @EnvironmentObject var authManager: AuthManager

    var body: some View {
        VStack {
            if authManager.isLoggedIn {
                Text("Hello, \(authManager.username)")
                Button("Log Out") {
                    authManager.logout()
                }
            } else {
                Button("Log In") {
                    authManager.login(user: "user")
                }
            }
        }
    }
}