如何在Kotlin Flow中实现RxJava2的onErrorResumeNext对应物，以返回另一个流？

问题描述

我想用Flow实施脱机-后备方法，首先尝试从远程源获取数据，如果失败，例如翻新引发网络异常，我想使用下面的代码从本地源获取数据

    return flow { emit(repository.fetchEntitiesFromRemote()) }
        .map {

            println("? getPostFlowOfflineLast() First map in thread: ${Thread.currentThread().name}")

            val data = if (it.isEmpty()) {
                repository.getPostEntitiesFromLocal()
            } else {
                repository.deletePostEntities()
                repository.savePostEntity(it)
                repository.getPostEntitiesFromLocal()
            }

            entityToPostMapper.map(data)
        }
        .catch { cause ->
            println("❌ getPostFlowOfflineLast() FIRST catch with error: $cause,in thread: ${Thread.currentThread().name}")
           flow { emit(repository.getPostEntitiesFromLocal()) }
        }
        .map { postList ->

            println("? getPostFlowOfflineLast() Second map in thread: ${Thread.currentThread().name}")

            ViewState<List<Post>>(
                status = Status.SUCCESS,data = postList
            )
        }
        .catch { cause: Throwable ->

            println("❌ getPostFlowOfflineLast() SECOND catch with error: $cause,in thread: ${Thread.currentThread().name}")

            flow {
                emit(
                    ViewState<List<Post>>(
                        Status.ERROR,error = cause
                    )
                )
            }
        }

但是它被异常卡住了

I: ❌ getPostFlowOfflineLast() FIRST catch with error: java.net.UnknownHostException: Unable to resolve host "jsonplaceholder.typicode.com": No address associated with hostname,in thread: main

如果存储库功能是可观察的，那么应该具有什么类似于RxJava onResumeNext的可观察的正确实现？

onErrorResumeNext { _: Throwable ->
     Observable.just(repository.getPostEntitiesFromLocal())
}

解决方法

发现我可以将emitAll与流一起使用，甚至可以连续多次进行流。

    .catch { cause ->
        println("❌ getPostFlowOfflineLast() FIRST catch with error: $cause,in thread: ${Thread.currentThread().name}")
        emitAll(flow { emit(repository.getPostEntitiesFromLocal()) })
    }
    .map {
        if (!it.isNullOrEmpty()) {
            entityToPostMapper.map(it)
        } else {
            throw EmptyDataException("No data is available!")
        }
    }
    .map { postList ->
        println("? getPostFlowOfflineLast() Third map in thread: ${Thread.currentThread().name}")
        ViewState(status = Status.SUCCESS,data = postList)
    }
    .catch { cause: Throwable ->
        println("❌ getPostFlowOfflineLast() SECOND catch with error: $cause,in thread: ${Thread.currentThread().name}")
        emitAll(flow { emit(ViewState(Status.ERROR,error = cause)) })
    }