RxStateMachine

stateMachine is an operator on RxJava 2's Observable which transforms the source stream into the resulting stream that emits the initialState first and then sequentially applies the reducer to the previous state and an emission from the source stream to emit a new state.

    private val reducer: (State, Action) -> Observable<State> = { state, action ->
        when {
            action is INCREMENT -> Observable.just(state + 1)
            action is DECREMENT && state > 0 -> Observable.just(state - 1)
            else -> Observable.just(state)
        }
    }

    @Test
    fun stateMachine() {
        val o = RecordingObserver<State>()
        val action = PublishSubject.create<Action>()
        action.stateMachine(0, reducer).subscribe(o)

        assertEquals(0, o.takeNext())

        action.onNext(INCREMENT)
        assertEquals(1, o.takeNext())
        action.onNext(INCREMENT)
        assertEquals(2, o.takeNext())

        action.onNext(DECREMENT)
        assertEquals(1, o.takeNext())
        action.onNext(DECREMENT)
        assertEquals(0, o.takeNext())

        action.onNext(DECREMENT)
        o.assertNoMoreEvents()
    }

Download

stateMachine operator:

implementation 'com.shionfujie.rxstatemachine:rxstatemachine:1.0.0'

License

Copyright 2019 Shion Tonatiuh Fujie

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.