Lasso Intro Article

LoginScreenModule.swift

enum LoginScreenModule: ScreenModule {
  
  enum Action: Equatable {
    case didUpdateUsername(String)
    case didUpdatePassword(String)
    case didTapLogin
  }
  
  enum Output: Equatable {
    case userDidLogin
  }
  
  struct State: Equatable {
    var username: String = ""
    var password: String = ""
    var error: String? = nil
  }
  
  static var defaultInitialState: State {
    return State()
  }
  
}

LoginScreenStore.swift

final class LoginScreenStore: LassoStore<LoginScreenModule> {
  
  override handleAction(_ action: Action) {
    switch action {
    
    case .didUpdateUsername(let username):
      update { state in
      	state.username = username
      }
      
    case .didUpdatePassword(let password):
      update { state in
      	state.password = password
      }
      
     case .didTapLogin:
      LoginService.login(state.username,
                         state.password) { [weak self] success in
        self?.update { state in
          state.error = success ? nil : "Invalid login"
        }
        if success {
          self?.dispatchOutput(.userDidLogin)
        }
      }
    }
  }
  
}

LoginScreenViewController.swift

final class LoginScreenViewController: UIViewController, LassoView {
  
  let store: LoginScreenModule.ViewStore
  
  init(_ store: ViewStore) {
    self.store = store
    // omitted for clarity: create/layout the UIKit controls
    setupBindings()
  }
  
  private let usernameField: UITextField
  private let passwordField: UITextField
  private let errorLabel: UILabel
  private let loginButton: UIButton
	
	private func setupBindings() {
    // State change inputs:
    store.observeState(\.username) { [weak self] username in
      self?.usernameField.text = username
    }
    store.observeState(\.password) { [weak self] password in
      self?.passwordField.text = password
    }
    store.observeState(\.error) { [weak self] error in
      self?.errorLabel.text = error
    }
    
    // Action outputs:
    usernameField.bindTextDidChange(to: store) { text in
      .didUpdateUsername(text)
    }
    passwordField.bindTextDidChange(to: store) { text in
      .didUpdatePassword(text)
    }
    loginButton.bind(to: store, action: .didTapLogin)
  }
  
}

LoginService.swift

enum LoginService {
  static func login(_ username: String,
                    _ password: String,
                    completion: @escaping (Bool) -> Void) {
    ...
  }
}