Login form sample with Functional Reactive Programming + DataBinding by Kotlin + Android

fragment_loginform.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <import type="mobi.pooh3.androidxsimplereactiveporgramming.loginform.Msg"/>
        <import type="io.reactivex.processors.PublishProcessor"/>
        <variable
            name="viewModel"
            type="mobi.pooh3.androidxsimplereactiveporgramming.loginform.LoginFormViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/topic"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".loginform.LoginFormFragment">


        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="e-mail"
            app:layout_constraintBottom_toTopOf="@+id/editText"
            app:layout_constraintStart_toStartOf="@+id/editText"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_chainStyle="packed" />


        <EditText
            android:id="@+id/editText"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:ems="10"
            android:hint="enter e-mail address"
            android:inputType="textEmailAddress"
            android:onTextChanged="@{(text, start, before, count) ->  viewModel.event.onNext(Msg.email(text))}"
            app:layout_constraintBottom_toTopOf="@+id/textView2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView" />


        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="24dp"
            android:text="pass word"
            app:layout_constraintBottom_toTopOf="@+id/editText2"
            app:layout_constraintStart_toStartOf="@+id/editText"
            app:layout_constraintTop_toBottomOf="@+id/editText" />

        <EditText
            android:id="@+id/editText2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:ems="10"
            android:hint="enter pass word"
            android:inputType="textPassword"
            android:onTextChanged="@{(text, start, before, count) ->  viewModel.event.onNext(Msg.passWord(text))}"
            app:layout_constraintBottom_toTopOf="@+id/button2"
            app:layout_constraintStart_toStartOf="@+id/textView2"
            app:layout_constraintTop_toBottomOf="@+id/textView2" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="64dp"
            android:layout_marginBottom="8dp"
            android:text="Button"
            android:onClick="@{() -> viewModel.event.onNext(Msg.Submit.INSTANCE)}"
            android:enabled="@{viewModel.submitEnable}"
            app:layout_constraintBottom_toTopOf="@+id/guideline"
            app:layout_constraintEnd_toEndOf="@+id/editText2"
            app:layout_constraintTop_toBottomOf="@+id/editText2" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_begin="344dp" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

LoginForm01.kt

class LoginFormFragment : Fragment() {

    companion object {
        fun newInstance() = LoginFormFragment()
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        requireActivity().title = "Simple Login Form"
        return bindingWith(LoginFormFragmentBinding.inflate(inflater)) {
            viewModel = provideViewModel()
        }.also {
            requireNotNull(it.viewModel).submitResult.observe(this@LoginFormFragment, Observer {
                Toast.makeText(requireContext(), "submitted!", Toast.LENGTH_SHORT).apply {
                    setGravity(Gravity.CENTER, 0, -300)
                }.show()
            })
        }.root
    }

}

sealed class Msg {
    data class Email(val email: CharSequence) : Msg()
    data class PassWord(val pw: CharSequence) : Msg()
    object Submit : Msg()

    companion object {
        @JvmStatic fun email(email: CharSequence) = Email(email)
        @JvmStatic fun passWord(pw: CharSequence) = PassWord(pw)
    }
}

data class Model(
    val email: CharSequence,
    val passWord: CharSequence,
    val response: Result
)

sealed class Result {
    object Nothing : Result()
    object Success : Result()
    object Error : Result()
}

@Suppress("MoveLambdaOutsideParentheses")
class LoginFormViewModel : ViewModel() {
    // ユーザからのイベントを通知
    val event = publishProcessor<Msg>()

    // ユーザからのイベント処理結果を観測する
    val submitEnable: LiveData<Boolean>
    val submitResult: LiveData<Result>

    init {
        val state = behaviorProcessor(Model(email = "", passWord = "", response = Result.Nothing))
        // Msg Model -> Model, distinctUntilChangedで連打対策
        update(event.distinctUntilChanged(), state, { msg, model ->
            when (msg) {
                is Msg.Email -> model.copy(email = msg.email)
                is Msg.PassWord -> model.copy(passWord = msg.pw)
                // APIの処理通信結果を入れる。今回はSuccess固定
                is Msg.Submit -> model.copy(response = Result.Success)
            }
        })
        // ボタンを有効にする条件の処理を挟む（現在は二つのパラメータが空ではないこと）
        submitEnable = state.map { it.email.isNotBlank() && it.passWord.isNotBlank() }.toLiveData()
        submitResult = state.filter { it.response !is Result.Nothing }.map { it.response }.toLiveData()
    }
}

LoginForm02.kt

class LoginFormFragment : Fragment() {

    companion object {
        fun newInstance() = LoginFormFragment()
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        requireActivity().title = "Simple Login Form"
        return bindingWith(LoginFormFragmentBinding.inflate(inflater)) {
            viewModel = provideViewModel()
        }.also {
            requireNotNull(it.viewModel).submitResult.observe(this@LoginFormFragment, Observer {
                Toast.makeText(requireContext(), "submitted!", Toast.LENGTH_SHORT).apply {
                    setGravity(Gravity.CENTER, 0, -300)
                }.show()
            })
        }.root
    }

}

sealed class Msg {
    data class Email(val email: CharSequence) : Msg()
    data class PassWord(val pw: CharSequence) : Msg()
    object Submit : Msg()

    companion object {
        @JvmStatic fun email(email: CharSequence) = Email(email)
        @JvmStatic fun passWord(pw: CharSequence) = PassWord(pw)
    }
}

sealed class Result {
    object Nothing : Result()
    object Success : Result()
    object Error : Result()
}

data class LFInputs(
    val event: Flowable<Msg>
) : Inputs

data class LFOutputs(
    val submitEnable: Flowable<Boolean>,
    val submitResult: Flowable<Result>
) : Outputs

interface LoginForm : Processor<LFInputs, LFOutputs>

@Suppress("MoveLambdaOutsideParentheses")
class LoginFormViewModel : ViewModel(), LoginForm {
    // ユーザからのイベントを通知
    val event = publishProcessor<Msg>()
    // ユーザからのイベント処理結果を観測する
    val submitEnable: LiveData<Boolean>
    val submitResult: LiveData<Result>

    init {
        val outputs = create(LFInputs(event = event.distinctUntilChanged()))
        submitEnable = outputs.submitEnable.toLiveData()
        submitResult = outputs.submitResult.toLiveData()
    }

    override fun create(inputs: LFInputs): LFOutputs {

        val allValid = checkInputs(inputs.event)

        val submitResult = attemptLogin(inputs.event)

        return LFOutputs(
            submitEnable = allValid,
            submitResult = submitResult
        )
    }

    companion object {
        private fun checkInputs(
            sEvent: Flowable<Msg>
        ): Flowable<Boolean> {
            val emailAndPassWord = behaviorProcessor(false to false)
            // ボタンを有効にする条件の処理を挟む（現在は二つのパラメータが空ではないこと）
            update(sEvent, emailAndPassWord, { msg, pair ->
                when (msg) {
                    is Msg.Email -> pair.copy(first = msg.email.isNotBlank())
                    is Msg.PassWord -> pair.copy(second = msg.pw.isNotBlank())
                    is Msg.Submit -> pair
                }
            })
            return emailAndPassWord
                .distinctUntilChanged()
                .map { (emailValid, pwValid) -> emailValid && pwValid }
        }

        private fun attemptLogin(sEvent: Flowable<Msg>): Flowable<Result> {
            return sEvent.map {
                when (it) {
                    is Msg.Email -> Result.Nothing
                    is Msg.PassWord -> Result.Nothing
                    is Msg.Submit -> Result.Success
                }
            }
                .distinctUntilChanged()
                .filter { it != Result.Nothing }
        }
    }
}

Addotional

fun <T : Any> publishProcessor(init: (PublishProcessor<T>.() -> Unit)? = null): PublishProcessor<T> {
    return PublishProcessor.create<T>().apply { if (init != null) init() }
}

fun <T : Any> behaviorProcessor(defV: T? = null, init: (BehaviorProcessor<T>.() -> Unit)? = null): BehaviorProcessor<T> {
    return if (defV != null) {
        BehaviorProcessor.createDefault(defV).apply { if (init != null) init() }
    } else {
        BehaviorProcessor.create<T>().apply { if (init != null) init() }
    }
}

@Suppress("MoveLambdaOutsideParentheses")
inline fun <T, R> update(input: Flowable<T>, total: BehaviorProcessor<R>, crossinline combiner: (T, R) -> R) {
    return input.withLatestFrom(total, { input_, total_ -> combiner(input_, total_) }).subscribe(total)
}

fun <T: Any> Publisher<T>.toLiveData() = LiveDataReactiveStreams.fromPublisher(this)

fun <VDB : ViewDataBinding> LifecycleOwner.bindingWith(binding: VDB, init: VDB.() -> Unit): VDB {
    binding.setLifecycleOwner(this)
    binding.init()
    return binding
}

inline fun <reified VM : ViewModel> Fragment.provideViewModel(): VM = ViewModelProviders.of(this).get(VM::class.java)


interface Inputs
interface Outputs
interface Processor<IN : Inputs, OUT: Outputs> {
    fun create(inputs: IN): OUT
}