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)
  }
}

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 ?