class ViewChangeTextSubscribe(val view: TextView) : ObservableOnSubscribe<String> {

    override fun subscribe(emitter: ObservableEmitter<String>) {

        if (Looper.getMainLooper() != Looper.myLooper()) {
            throw IllegalStateException(
                "Must be called on the main thread. Current thread: ${Thread.currentThread()}"
            )
        }

        val watcher = object : TextWatcher {
            override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) = Unit

            override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
                if (emitter.isDisposed.not()) emitter.onNext(s.toString())
            }

            override fun afterTextChanged(s: Editable) = Unit
        }

        view.addTextChangedListener(watcher)
        if (emitter.isDisposed) view.removeTextChangedListener(watcher)
        emitter.onNext(view.text.toString())
    }
}


Экстеншен ф-ция:
inline fun TextInputEditText.textChanges(): Observable<String> = Observable.create(ViewChangeTextSubscribe(this))

Пример использования:

        observFirstName = tietFirstName.textChanges()
        observLastName = tietLastName.textChanges()
        observPatronymic = tietPatronymic.textChanges()
        observBirthday = tietBirthday.textChanges()
        observPhone = tietPhone.textChanges()

        presenter.fieldValidation(
            observFirstName,
            observLastName,
            observPatronymic,
            observBirthday,
            observPhone
        )



И пРезентер:




  override fun fieldValidation(
        observFirstName: Observable<String>,
        observLastName: Observable<String>,
        observPatronymic: Observable<String>,
        observBirthday: Observable<String>,
        observPhone: Observable<String>
    ) {
        disposables += Observable.combineLatest(
            observFirstName.map { it },
            observLastName.map { it },
            observPatronymic.map { it },
            observBirthday.map { it },
            observPhone.map { it },
            Function5 { firstName: String,
                        lastName: String,
                        patronymic: String,
                        birthday: String,
                        phone: String ->
                firstName.isNotBlank() &&
                        lastName.isNotBlank() &&
                        patronymic.isNotBlank() &&
                        birthday.isNotBlank() &&
                        phone.isNotBlank()
            }
        )
            .observeOn(rxSchedulers.ui)
            .subscribe { view.enabledRegistryButton(it) }
    }