ViewModles

ViewModel

/**
 * View Model for the [UserActivity]
 */
class UserViewModel(private val dataSource: UserDao) : ViewModel() {

    /**
     * Get the user name of the user.

     * @return a [Flowable] that will emit every time the user name has been updated.
     */
    // for every emission of the user, get the user name
    fun userName(): Flowable<String> {
        return dataSource.getUserById(USER_ID)
                .map { user -> user.userName }
    }

    /**
     * Update the user name.
     * @param userName the new user name
     * *
     * @return a [Completable] that completes when the user name is updated
     */
    fun updateUserName(userName: String): Completable {
        return Completable.fromAction {
            val user = User(USER_ID, userName)
            dataSource.insertUser(user)
        }
    }

    companion object {
        // using a hardcoded value for simplicity
        const val USER_ID = "1"
    }
}

ViewModelFactory

/**
 * Factory for ViewModels
 */
class ViewModelFactory(private val dataSource: UserDao) : ViewModelProvider.Factory {

    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(UserViewModel::class.java)) {
            return UserViewModel(dataSource) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

/**
 * Main screen of the app. Displays a user name and gives the option to update the user name.
 */
class UserActivity : AppCompatActivity() {

    private lateinit var viewModelFactory: ViewModelFactory

    private lateinit var viewModel: UserViewModel

    private val disposable = CompositeDisposable()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_user)

        viewModelFactory = Injection.provideViewModelFactory(this)
        viewModel = ViewModelProviders.of(this, viewModelFactory).get(UserViewModel::class.java)
        update_user_button.setOnClickListener { updateUserName() }
    }

    override fun onStart() {
        super.onStart()
        // Subscribe to the emissions of the user name from the view model.
        // Update the user name text view, at every onNext emission.
        // In case of error, log the exception.
        disposable.add(viewModel.userName()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe({ this.user_name.text = it },
                        { error -> Log.e(TAG, "Unable to get username", error) }))
    }

    override fun onStop() {
        super.onStop()

        // clear all the subscription
        disposable.clear()
    }

    private fun updateUserName() {
        val userName = user_name_input.text.toString()
        // Disable the update button until the user name update has been done
        update_user_button.isEnabled = false
        // Subscribe to updating the user name.
        // Enable back the button once the user name has been updated
        disposable.add(viewModel.updateUserName(userName)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe({ update_user_button.isEnabled = true },
                        { error -> Log.e(TAG, "Unable to update username", error) }))
    }

    companion object {
        private val TAG = UserActivity::class.java.simpleName
    }
}