Dependency injection example of a service in MVVM

LoginServiceImplementation.swift

// LoginService Protocol
protocol LoginService: AnyObject {
    func authenticateUser(request: LoginRequest) - > UserResponse
}

// Concrete implementation
class LoginServiceImplementation: LoginService {

    func authenticateUser(request: LoginRequest) - > UserResponse {
        // create the url request
        // use the singleton here
        HttpUtility.shared.get {
            // handle response	
        }
    }
}

LoginViewModel.swift

protocol LoginViewModel: AnyObject {
func authenticateUser()
}

class LoginViewModelImplementation: LoginViewModel {

    private let loginService: LoginService

    // injecting the dependency
    init(_service: LoginService) {
        self.loginService = _service
    }

    func authenticateUser() {
        // code
        self.loginService.authenticateUser(request) {
            // handle response
        }
    }
}

ServiceFactory.swift

// factory to return the required protocol
class ServiceFactory {

  func createLoginService() -> LoginService {
  	return LoginServiceImplementation()
  }
}

ViewModelFactory.swift

class ViewModelFactory {

func createLoginViewModel -> LoginViewModel {
  let service = ServiceFactory().createLoginService()
  return LoginViewModelImplementation(_service: service)
  
}