RxJava实时数据错误处理

Question

So, in my android project I am using RxJava in the repository layer then I convert it to live data in the view Model, but I am having an exception when my stream emits an error. It has something to do with this remark from the Android Documentation :

fromPublisher

LiveData<T> fromPublisher (Publisher<T> publisher)

Creates an Observable LiveData stream from a ReactiveStreams publisher.

When the LiveData becomes active, it subscribes to the emissions from the Publisher.

When the LiveData becomes inactive, the subscription is cleared. LiveData holds the last value emitted by the Publisher when the LiveData was active.

Therefore, in the case of a hot RxJava Observable, when a new LiveData Observer is added, it will automatically notify with the last value held in LiveData , which might not be the last value emitted by the Publisher.

Note that LiveData does NOT handle errors and it expects that errors are treated as states in the data that's held. In case of an error being emitted by the publisher, an error will be propagated to the main thread and the app will crash.

How can I handle the stream error? PS: I am using a Kotlin extension to convert to Live data

fun <T> Observable<T>.toLiveData(backPressureStrategy: BackpressureStrategy =
                                                BackpressureStrategy.LATEST) :  LiveData<T> {
Log.d("RxJava",this.toString())
return LiveDataReactiveStreams.fromPublisher(this.toFlowable(backPressureStrategy))

Answer 1

As a newbie, i'm not sure about this solution. But it works. So, if it's bad, please comment to say why and provide an alternative.

Use this :

data class DataWithStates<T>(
    val data: T? = null,
    val states: Throwable? = null
)

Sample for ViewModel :

fun getUsers(): LiveData<DataWithStates<List<User>>> {
    return LiveDataReactiveStreams.fromPublisher(
        userRepository
            .getAll()
            .map { lstUser -> DataWithStates(lstUser) }
            .onErrorReturn { ex -> DataWithStates(states = ex) }
            .toFlowable(BackpressureStrategy.LATEST))
}

Maybe it's better to move .map and .onErrorReturn in the repository.

Edit : alternatively, you can use a lambda to listen for error.

fun getUsers(onError: () -> Unit = {}): LiveData<List<User>> {
    return LiveDataReactiveStreams.fromPublisher(
        userRepository
            .getAll()
            .doOnError { onError() }
            .toFlowable(BackpressureStrategy.LATEST))
}

Answer 2

如果您使用的是实时数据（Android architecure组件）。最好使用其预定义的Oberserver（在建筑组件中）。否则，您完全只需要使用RX android clases