@EnvironmentObject

1. Giới thiệu

@EnvironmentObject chia sẻ data xuyên suốt View hierarchy.

class AppSettings: ObservableObject {
    @Published var isDarkMode = false
    @Published var language = "en"
}

@main
struct MyApp: App {
    @StateObject var settings = AppSettings()

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

2. Inject và Access

Inject tại root

ContentView()
    .environmentObject(settings)

Access trong child views

struct ChildView: View {
    @EnvironmentObject var settings: AppSettings

    var body: some View {
        Text("Dark mode: \(settings.isDarkMode ? "On" : "Off")")
    }
}

3. Ví dụ: Theme Manager

class ThemeManager: ObservableObject {
    @Published var isDarkMode = false
    @Published var accentColor = Color.blue

    var backgroundColor: Color {
        isDarkMode ? .black : .white
    }

    var textColor: Color {
        isDarkMode ? .white : .black
    }
}

struct RootView: View {
    @StateObject var themeManager = ThemeManager()

    var body: some View {
        TabView {
            HomeView()
            SettingsView()
        }
        .environmentObject(themeManager)
        .preferredColorScheme(themeManager.isDarkMode ? .dark : .light)
    }
}

struct HomeView: View {
    @EnvironmentObject var theme: ThemeManager

    var body: some View {
        VStack {
            Text("Home")
                .foregroundColor(theme.textColor)
        }
        .background(theme.backgroundColor)
    }
}

struct SettingsView: View {
    @EnvironmentObject var theme: ThemeManager

    var body: some View {
        Form {
            Toggle("Dark Mode", isOn: $theme.isDarkMode)

            ColorPicker("Accent Color", selection: $theme.accentColor)
        }
    }
}

4. User Session

class UserSession: ObservableObject {
    @Published var currentUser: User?
    @Published var isAuthenticated = false

    func login(email: String, password: String) async throws {
        // API call
        currentUser = User(name: "John", email: email)
        isAuthenticated = true
    }

    func logout() {
        currentUser = nil
        isAuthenticated = false
    }
}

struct AppRootView: View {
    @StateObject var session = UserSession()

    var body: some View {
        Group {
            if session.isAuthenticated {
                MainTabView()
            } else {
                LoginView()
            }
        }
        .environmentObject(session)
    }
}

struct ProfileView: View {
    @EnvironmentObject var session: UserSession

    var body: some View {
        VStack {
            if let user = session.currentUser {
                Text("Welcome, \(user.name)")
            }

            Button("Logout") {
                session.logout()
            }
        }
    }
}

5. Shopping Cart

class CartManager: ObservableObject {
    @Published var items: [CartItem] = []

    var total: Double {
        items.reduce(0) { $0 + $1.price * Double($1.quantity) }
    }

    var itemCount: Int {
        items.reduce(0) { $0 + $1.quantity }
    }

    func add(_ product: Product) {
        if let index = items.firstIndex(where: { $0.productId == product.id }) {
            items[index].quantity += 1
        } else {
            items.append(CartItem(productId: product.id, name: product.name, price: product.price, quantity: 1))
        }
    }

    func remove(_ item: CartItem) {
        items.removeAll { $0.id == item.id }
    }
}

struct ProductCard: View {
    let product: Product
    @EnvironmentObject var cart: CartManager

    var body: some View {
        VStack {
            Text(product.name)
            Text("$\(product.price, specifier: "%.2f")")

            Button("Add to Cart") {
                cart.add(product)
            }
            .buttonStyle(.borderedProminent)
        }
    }
}

struct CartBadge: View {
    @EnvironmentObject var cart: CartManager

    var body: some View {
        ZStack(alignment: .topTrailing) {
            Image(systemName: "cart")

            if cart.itemCount > 0 {
                Text("\(cart.itemCount)")
                    .font(.caption2)
                    .foregroundColor(.white)
                    .padding(4)
                    .background(Circle().fill(.red))
                    .offset(x: 8, y: -8)
            }
        }
    }
}

6. Multiple EnvironmentObjects

struct App: App {
    @StateObject var userSession = UserSession()
    @StateObject var settings = AppSettings()
    @StateObject var cart = CartManager()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(userSession)
                .environmentObject(settings)
                .environmentObject(cart)
        }
    }
}

7. Preview với EnvironmentObject

#Preview {
    ProductCard(product: Product(name: "iPhone", price: 999))
        .environmentObject(CartManager())
}

8. So sánh

Feature	@StateObject	@EnvironmentObject
Tạo object	✅	❌
Pass qua init	❌	❌
Inject	-	.environmentObject()
Scope	View đó	Toàn bộ subtree

---

📝 Tóm tắt

• Inject với .environmentObject(object)
• Access với @EnvironmentObject var obj: Type
• Dùng cho global state: theme, user session, cart
• Phải inject trước khi access (crash nếu không có)
• Dùng chung reference, thay đổi affect tất cả views