【Kotlin/Android】RxJavaでエラーハンドリングする方法！

val observable = Observable.create<Int> { emitter ->
    Log.d("RxJava", "ストリーム開始")
    emitter.onNext(1)
    emitter.onNext(2)
    emitter.onError(RuntimeException("エラー発生"))
}

observable
    .onErrorReturn { throwable -> 
      // エラーの種類によって返す値をコントロールできる
      if (throwable is RuntimeException) {
        -1 
      } else {
        -2
      }
    }
    .doOnSubscribe { Log.d("RxJava", "観測開始") }
    .doOnNext { Log.d("RxJava", "Received: $it") }
    .doOnError { Log.d("RxJava", "Error: ${it.message}") }
    .doOnComplete { Log.d("RxJava", "Completed") }
    .subscribe(
        { /* onNext */ },
        { /* onError */ },
        { /* onComplete */ }
    )
    .addTo(compositeDisposable)

観測開始
ストリーム開始
Received: 1
Received: 2
Received: -1
Completed

observable
    .onErrorReturnItem(3) // 固定値を返す
    .doOnSubscribe { Log.d("RxJava", "観測開始") }
    .doOnNext { Log.d("RxJava", "Received: $it") }
    .doOnError { Log.d("RxJava", "Error: ${it.message}") }
    .doOnComplete { Log.d("RxJava", "Completed") }
    .subscribe(
        { /* onNext */ },
        { /* onError */ },
        { /* onComplete */ }
    )
    .addTo(compositeDisposable)

観測開始
ストリーム開始
Received: 1
Received: 2
Received: 3
Completed

 observable
    // 引数は明示的に型を指定しないとエラーになる
    .onErrorResumeNext { throwable: Throwable ->
        Log.d("RxJava", "Error: ${throwable.message}")
        // 異なるObservableを返す
        Observable.just(4, 5, 6)
    }
    .doOnSubscribe { Log.d("RxJava", "観測開始") }
    .doOnNext { Log.d("RxJava", "Received: $it") }
    .doOnError { Log.d("RxJava", "Error: ${it.message}") }
    .doOnComplete { Log.d("RxJava", "Completed") }
    .subscribe(
        { /* onNext */ },
        { /* onError */ },
        { /* onComplete */ }
    )
    .addTo(compositeDisposable)

観測開始
ストリーム開始
Received: 1
Received: 2
Received: 4
Received: 5
Received: 6
Completed

val observable = Observable.create { emitter ->
    Log.d("RxJava", "ストリーム開始")
    emitter.onNext(1)
    emitter.onNext(2)
    // RuntimeExceptionでは発生しない
    // emitter.onError(RuntimeException("エラー発生"))
    emitter.onError(Exception("エラー発生"))
}

observable
    .onExceptionResumeNext(Observable.just(4, 5, 6))
    .doOnSubscribe { Log.d("RxJava", "観測開始") }
    .doOnNext { Log.d("RxJava", "Received: $it") }
    .doOnError { Log.d("RxJava", "Error: ${it.message}") }
    .doOnComplete { Log.d("RxJava", "Completed") }
    .subscribe(
        { /* onNext */ },
        { /* onError */ },
        { /* onComplete */ }
    )
    .addTo(compositeDisposable)

観測開始
ストリーム開始
Received: 1
Received: 2
Received: 4
Received: 5
Received: 6
Completed

.retry(3)

.doOnError { Log.d("RxJava", "Error: ${it.message}") }