MVVM Pattern

1. Overview

View ←→ ViewModel ←→ Model
UI       Logic        Data

2. Model

struct User: Identifiable, Codable {
    let id: Int
    let name: String
    let email: String
}

3. ViewModel

@MainActor
class UserListViewModel: ObservableObject {
    @Published var users: [User] = []
    @Published var isLoading = false
    @Published var error: String?

    private let service: UserService

    init(service: UserService = UserService()) {
        self.service = service
    }

    func loadUsers() async {
        isLoading = true
        error = nil

        do {
            users = try await service.fetchUsers()
        } catch {
            self.error = error.localizedDescription
        }

        isLoading = false
    }

    func deleteUser(_ user: User) async {
        do {
            try await service.delete(user)
            users.removeAll { $0.id == user.id }
        } catch {
            self.error = error.localizedDescription
        }
    }
}

4. View

struct UserListView: View {
    @StateObject var viewModel = UserListViewModel()

    var body: some View {
        Group {
            if viewModel.isLoading {
                ProgressView()
            } else if let error = viewModel.error {
                Text(error).foregroundColor(.red)
            } else {
                List(viewModel.users) { user in
                    UserRow(user: user)
                }
            }
        }
        .task {
            await viewModel.loadUsers()
        }
    }
}

5. Benefits

• Testable: ViewModel có thể test riêng
• Reusable: Logic tách khỏi UI
• Maintainable: Clear separation

---

📝 Best Practices

• ViewModel là @MainActor cho UI updates
• Dùng @StateObject khi tạo ViewModel
• Dùng @ObservedObject khi nhận từ parent