Kotlin - MutableStateFlow发射从未收到过
Kotlin - MutableStateFlow发射从未收到过
提问于 2021-01-13 13:47:42
当我在不同的片段中更改GameData的GameData属性时，我可以看到在存储库的侦听器中收到了更改，但是当我导航回片段时，当我使用MutableStateFlow时，视图模型从未收到更新的值。
奇怪的是，当我将流更改为MutableSharedFlow时，突然间视图模型也开始获得更新的值。有人知道为什么会发生这种事吗？我需要在这里使用MutableStateFlow，但它不起作用。
仓库：
private val gameDataListResultMutableFlow: MutableStateFlow<Result<List<GameData>>> = MutableStateFlow(Result.Loading)
override suspend fun observeGameDataList(): Flow<Result<List<GameData>>>
{
CoroutineScope(Dispatchers.IO + coroutineContext).launch {
localGameDataSource.observeGameDataList().collectLatest{
if(it is Result.Success)
{
Timber.d("local data change favorite value of item 0: ${it.data[0].isInFavorites}")
}
gameDataListResultMutableFlow.emit(it)
}
}
}视图模型
private suspend fun observeGameListResult()
{
gameRepository.observeGameDataList().collect{
if(it is Result.Success)
Timber.d("data change received in viewmodel value of item 0: ${it.data[0].isInFavorites}")
gameListResultMutableLiveData.postValue(it)
}
}
fun getGameListResultLiveData(): LiveData<Result<List<GameData>>>
{
launch(coroutineContext) {
observeGameListResult()
}
return gameListResultMutableLiveData
}在使用StateFlow时记录
LOADING THE INITIAL STATE, ISFAVORITE VALUE IS TRUE
D/DefaultGameRepository: local data change favorite value of item 0: true
D/GameListViewModel: data change received in viewmodel value of item 0: true
SWITCHING TO ANOTHER FRAGMENT TO CHANGE THE ISFAVORITE'S VALUE TO FALSE, WHICH IS RECEIVED ONLY BY
THE LOCAL SOURCE LISTENER
D/DefaultGameRepository: local data change the favorite value of item 0: false
SWITCHING BACK TO THE INITIAL FRAGMENT AND THE UPDATED VALUE OF THE ISFAVORITE REFLECTED ON THE LOCAL SOURCE LISTENER BUT NOT ON THE VIEWMODEL LISTENER---
D/GameListViewModel: data change received in viewmodel value of item 0: true
D/DefaultGameRepository: local data change the favorite value of item 0: false使用时的SharedFlow日志：
LOADING THE INITIAL STATE, ISFAVORITE VALUE IS TRUE
D/DefaultGameRepository: local data change the favorite value of item 0: true
D/GameListViewModel: data change received in viewmodel value of item 0: true
SWITCHING TO ANOTHER FRAGMENT TO CHANGE THE ISFAVORITE'S VALUE TO FALSE, WHICH IS RECEIVED BY LOCAL
SOURCE AND THE VIEWMODEL LISTENER
D/DefaultGameRepository: local data change the favorite value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false
SWITCHING BACK TO THE INITIAL FRAGMENT AND THE UPDATED VALUE OF THE ISFAVORITE REFLECTED ON THE
VIEWMODEL
D/DefaultGameRepository: local data change the favorite value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false
D/GameListViewModel: data change received in viewmodel value of item 0: false回答 1
Stack Overflow用户
回答已采纳
发布于 2021-01-13 14:09:44
是的，所以可能的主要原因是，除非要发出的提议对象不等于旧值，否则MutableStateFlow不会发出。然而，MutableSharedFlow总是会发出，因为它的发射逻辑没有distinctUntilChanged()等于逻辑。
来自SharedFlow文档：
强基于等式的合并
状态流中的值以类似于distinctUntilChanged运算符的方式使用Any.equals比较合并。它用于将传入的更新合并为MutableStateFlow中的值，并在新值等于先前发出的值时抑制向收集器发送值。未指定违反Any.equals合同的类的状态流行为。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/65703272
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