LoginViewModel.kt

class LoginViewModel @Inject constructor(private val loginGateway: LoginGateway) : ViewModel() {

    val emailField = ObservableField<String>()
    val passwordField = ObservableField<String>()

    val isSignInButtonEnabled = ObservableBoolean()

    val isProgressBarVisible = ObservableBoolean()

    val navigateToForgotPasswordPage = SingleLiveEvent<Unit>()

    val navigateToNextScreen = SingleLiveEvent<Unit>()

    val showErrorToast = SingleLiveEvent<String>()

    init {
        isSignInButtonEnabled.set(false)
        isProgressBarVisible.set(false)
    }

    fun onLoginButtonClicked() {
        isProgressBarVisible.set(true)
        loginGateway.login(emailField.get(), passwordField.get(), LoginCallbacks())
    }

    fun onForgotPasswordLabelClicked() {
        navigateToForgotPasswordPage.call()
    }

    fun emailTextChangedListener(): TextWatcher {
        return object : TextWatcherAdapter() {
            override fun afterTextChanged(s: Editable?) {
                validateInputFields()
            }
        }
    }

    fun passwordTextChangedListener(): TextWatcher {
        return object : TextWatcherAdapter() {
            override fun afterTextChanged(s: Editable?) {
                validateInputFields()
            }
        }
    }

    private fun validateInputFields() {
        isSignInButtonEnabled.set(!emailField.get().isNullOrBlank()
                && !passwordField.get().isNullOrBlank())
    }

    inner class LoginCallbacks : LoginGateway.LoginCallbacks {

        override fun onLoginSuccess() {
            navigateToNextScreen.call()
        }

        override fun onLoginError() {
            isProgressBarVisible.set(false)
            showErrorToast.call()
        }
    }
}