This is an example of Android development with VIPER in Kotlin

VIPER Android Example.kt

interface LoginContracts {
  interface View {
    fun showError(message: String)
  }
  
  interface Presenter {
    fun onDestroy()
    fun onLoginButtonPressed(username: String, password: String)
  }
  
  interface Interactor {
    fun unregister()
    fun login(username: String, password: String)
  }
  
  interface InteractorOutput {
    fun onLoginSuccess(user: User)
    fun onLoginError(message: String)
  }

  interface Router {
    fun unregister()
    fun presentHomeScreen(user: User)
  }
}

class LoginActivity: BaseActivity, LoginContracts.View {
  
  var presenter: LoginContracts.Presenter? = null
  
  //other fields

  override fun onCreate() {
    //...
    presenter = LoginPresenter(this)
    loginButton.setOnClickListener { onLoginButtonClicked() }
    //...
  }
  
  override fun onDestroy() {
    presenter?.onDestroy()
    presenter = null
    super.onDestroy()
  }

  private fun onLoginButtonClicked() {
    presenter?.onLoginButtonClicked(usernameEditText.text, passwordEditText.text)
  }
  
  fun showError(message: String) {
    //shows the error on a dialog
  }
}

class LoginPresenter(var view: LoginContracts.View?): LoginContracts.Presenter, LoginContracts.InteractorOutput {
    var interactor: LoginContracts.Interactor? = LoginInteractor(this)
    var router: LoginContracts.Router? = LoginRouter(view as? Activity)

    fun onDestroy() {
      view = null
      interactor?.unregister()
      interactor = null
      router?.unregister()
      router = null
    }

    fun onLoginButtonPressed(username: String, password: String) {
      interactor?.login(username, password)
    }

    fun onLoginSuccess(user: User) {
      router?.goToNextScreen(user)
    }
    
    fun onLoginError(message: String) {
      view?.showError(message)
    }
}

class LoginInteractor(var output: LoginContracts.InteractorOutput?): LoginContracts.Interactor {
  
  fun unregister() {
    output = null
  }
  
  fun login(username: String, password: String) {
    LoginApiManager.login(username, password)
                ?.subscribeOn(Schedulers.io())
                ?.observeOn(AndroidSchedulers.mainThread())
                ?.subscribe({ 
                          //does something with the user, like saving it or the token
                          output?.onLoginSuccess(it)
                          },
                        { output?.onLoginError(it.message ?: "Error!") })
  }
}

class LoginRouter(var activity: Activity?): LoginContracts.Router {
  
  fun unregister() {
    activity = null
  }
  
  fun presentHomeScreen(user: User) {
    val intent = Intent(view, HomeActivity::class.java)
    intent.putExtra(Constants.IntentExtras.USER, user)
    activity?.startActivity(intent)
  }
}

How much does it worth it now?
Given android have it's own view model architecture now.

What architecture exactly do you mean? They have Room, LiveObjects and some crappy navigation. How that solves the problem where to put Network communication for example?

In this example the presenter doesn't survive to rotation, right?

I think u can use view-model instead of presenter to handle config change in a better way.

How can I implement the navigation component: https://developer.android.com/guide/navigation ?

Visit this sample project on github and medium to better understanding

A Mini Uber with Kotlin Multiplatform + VIPER Architecture + Compose Multiplatform Architecture

Overview:

View → Composable screens observing StateFlow<UiState>.

Presenter → Extends ViewModel, processes events, updates state.

Interactor → Business logic (e.g., fetch drivers, request ride).

Router → Handles navigation between screens + result passing.

Entities → Models like DriverResponse, RideRequest.

• Navigation concerns stay separated in Router, not spread in the UI.

• Google map implementation, state management, and challenges in the compose multipaltform

github:

https://github.com/mahdizareeii/Mini-Uber

medium:

https://medium.com/@mahdizareeii/building-a-mini-uber-with-kotlin-multiplatform-viper-architecture-compose-multiplatform-1d3dd0a08399