android - 使用 launch() 范围时无法为 LiveData 变量赋值，但可以使用 runBlocking() 为 LiveData 赋值

Question

我有一个 LiveData 变量，我想在收到来自 HTTP 请求 的响应后为其赋值。我在 launch{} 范围内分配这个值。但是，当我测试代码以查看实际已分配值时，测试失败并指出该值为 null。

我尝试了另一种选择，即使用 runBlocking {} 范围而不是 launch {} 范围，并且我的测试用例通过了。用于网络的库是 Retrofit

下面是使用 launch() 并使测试用例失败的代码。

private var _state = MutableLiveData<State>()
val state: LiveData<State>
  get() = _state 

private var job = Job()

private val uiScope = CoroutineScope(job + Dispatchers.Main)

init {
    executeRequest(....)
}

// Test cases fails with this function
private fun executeRequest(params) {
  uiScope.launch {
    val deferred = repository.getApi()
        .requestAsync(params)

    try {
        val response = deferred.await()

        _state.value = StateSuccess(response)
    } catch (e: Exception) {
        _state.value = StateError("Failure: $e.message")
    }
  }
}

下面是使用 runBlocking() 并使测试用例通过的代码。

private var _state = MutableLiveData<State>()
val state: LiveData<State>
  get() = _state 

private var job = Job()

private val uiScope = CoroutineScope(job + Dispatchers.Main)

init {
    executeRequest(....)
}

// Test cases passes with this function
private fun executeRequest(params) {
  runBlocking {
    val deferred = repository.getApi()
        .requestAsync(params)

    try {
        val response = deferred.await()

        _state.value = StateSuccess(response)
    } catch (e: Exception) {
        _state.value = StateError("Failure: $e.message")
    }
  }
}

这是测试用例

val viewModel = MyViewModel(fakeClientRepository)

val observer = Observer<State> {}

try {
    viewModel.state.observeForever(observer)

    assert(viewModel.state.value == StateSuccess("success"))
} finally {
    viewModel.state.removeObserver(observer)
}

为什么 launch() 没有将值分配给 LiveData 变量？

Answer 1

尝试使用 Dispatchers.IO 调度程序，然后将值分配给 LiveData，使用 postValue() 而不是 value即

private fun executeRequest(params) {
  uiScope.launch {
    withContext(Dispatcher.IO){
 val deferred = repository.getApi()
        .requestAsync(params)
    try {
        val response = deferred.await()
        _state.postValue(RESPONSE)
    } catch (e: Exception) {
        _state.postValue(StateError("Failure: $e.message"))
    }

    }
  }
}