在干净的架构中并行调用多个api请求答案

【问题标题】：Call parallel multiple the api request in the clean architecture在干净的架构中并行调用多个api请求
【发布时间】：2022-01-05 05:55:39
【问题描述】：

我在 viewModel 中有 5 个要并行调用的 api 调用函数，我该怎么做？我将每个函数都放在WithContext(Dispachers.IO) 中，但它不起作用。我使用协程流来调用 api。注意：我使用了干净的架构模式，并且我只有一个用例

ViewModel 代码：

class MyJobsViewModel constructor(
    private val myJobsUseCases: MyJobsUseCases,
    private val clientNavigator: ClientNavigator
) : ViewModel(), ClientNavigator by clientNavigator {

    private val _state = mutableStateOf(MyJobsState())
    val state: State<MyJobsState> get() = _state


    private fun getAllJobs(
        offset: Int = 0,
        limit: Int = 10,
        type: JobTypeEnum = JobTypeEnum.ALL
    ) {
        myJobsUseCases.getJobsUseCase.invoke(offset = offset, limit = limit, type = type)
            .onEach {
                when (it) {
                    is Resource.Success -> _state.value =
                        state.value.copy(
                            isLoading = false,
                            allJobItems = it.data ?: JobItemsResponse()
                        )
                    is Resource.Error -> _state.value =
                        state.value.copy(
                            isLoading = false,
                            error = it.message ?: "An unexpected error occurred"
                        )
                    is Resource.Loading -> _state.value = state.value.copy(isLoading = true)
                }
            }.launchIn(viewModelScope)
    }

    private fun getActiveJobs(
        offset: Int = 0,
        limit: Int = 10,
        type: JobTypeEnum = JobTypeEnum.ALL
    ) {
        myJobsUseCases.getJobsUseCase.invoke(offset = offset, limit = limit, type = type)
            .onEach {
                when (it) {
                    is Resource.Success -> _state.value =
                        state.value.copy(
                            isLoading = false,
                            activeJobItems = it.data ?: JobItemsResponse()
                        )
                    is Resource.Error -> _state.value =
                        state.value.copy(
                            isLoading = false,
                            error = it.message ?: "An unexpected error occurred"
                        )
                    is Resource.Loading -> _state.value = state.value.copy(isLoading = true)
                }
            }.launchIn(viewModelScope)
    }

}

【问题讨论】：

标签： android kotlin-coroutines

【解决方案1】：

并行多个调用的最佳方式是关注structured concurrency principle。

例如，当你需要评估5个独立网络请求的结果时：

suspend fun fetchA(): Int { /* ... */ }
suspend fun fetchB(): Int { /* ... */ }
suspend fun fetchC(): Int { /* ... */ }
suspend fun fetchD(): Int { /* ... */ }
suspend fun fetchE(): Int { /* ... */ }

suspend fun overallResult(): Int = coroutineScope {
    val a = async { fetchA() }
    val b = async { fetchB() }
    val c = async { fetchC() }
    val d = async { fetchD() }
    val e = async { fetchE() }

    a.await() + b.await() + c.await() + d.await() + e.await()
}

或者当你需要进行 5 次独立的 api 调用而不返回任何值时：

suspend fun callA() { /* ... */ }
suspend fun callB() { /* ... */ }
suspend fun callC() { /* ... */ }
suspend fun callD() { /* ... */ }
suspend fun callE() { /* ... */ }

suspend fun makeCalls(): Unit = coroutineScope {
    launch { callA() }
    launch { callB() }
    launch { callC() }
    launch { callD() }
    launch { callE() }
}

launch 或 async 块中的包装函数会生成一个新的协程并并行执行。

coroutineScope 组织了可以使用启动和异步的区域。只有当每个子协程都完成时它才会完成。

【讨论】：