Android 后台线程上的实时数据转换

Question

我看到了但我不确定如何实施它，或者如果这是同一个问题，我有一个调解器实时数据，它会在其 2 个源实时数据更新或基础数据（Room db）更新，它似乎工作正常但如果数据更新很多，它会在 quick 连续刷新很多，我得到一个错误

Cannot run invalidation tracker. Is the db closed?
Cannot access database on the main thread since it may potentially lock the UI for a long period of time

这种情况不会每次都发生，只有在非常频繁地对数据库进行大量更新时才会发生uick 这就是视图模型的问题部分，

var search: MutableLiveData<String> = getSearchState()
val filters: MutableLiveData<MutableSet<String>> = getCurrentFiltersState()
val searchPokemon: LiveData<PagingData<PokemonWithTypesAndSpeciesForList>>

val isFiltersLayoutExpanded: MutableLiveData<Boolean> = getFiltersLayoutExpanded()

init {

    val combinedValues =
        MediatorLiveData<Pair<String?, MutableSet<String>?>?>().apply {
            addSource(search) {
                value = Pair(it, filters.value)
            }
            addSource(filters) {
                value = Pair(search.value, it)
            }
        }

    searchPokemon = Transformations.switchMap(combinedValues) { pair ->
        val search = pair?.first
        val filters = pair?.second
        if (search != null && filters != null) {
            searchAndFilterPokemonPager(search, filters.toList())
        } else null
    }.distinctUntilChanged()
}

@SuppressLint("DefaultLocale")
private fun searchAndFilterPokemonPager(search: String, filters: List<String>): LiveData<PagingData<PokemonWithTypesAndSpeciesForList>> {
    return Pager(
        config = PagingConfig(
            pageSize = 20,
            enablePlaceholders = false,
            maxSize = 60
        )
    ) {
        if (filters.isEmpty()){
            searchPokemonForPaging(search)
        } else {
            searchAndFilterPokemonForPaging(search, filters)
        }
    }.liveData.cachedIn(viewModelScope)
}

@SuppressLint("DefaultLocale")
private fun getAllPokemonForPaging(): PagingSource<Int, PokemonWithTypesAndSpecies> {
    return repository.getAllPokemonWithTypesAndSpeciesForPaging()
}

@SuppressLint("DefaultLocale")
private fun searchPokemonForPaging(search: String): PagingSource<Int, PokemonWithTypesAndSpeciesForList> {
    return repository.searchPokemonWithTypesAndSpeciesForPaging(search)
}

@SuppressLint("DefaultLocale")
private fun searchAndFilterPokemonForPaging(search: String, filters: List<String>): PagingSource<Int, PokemonWithTypesAndSpeciesForList> {
    return repository.searchAndFilterPokemonWithTypesAndSpeciesForPaging(search, filters)
}

错误实际上是由函数 searchPokemonForPaging 引发的

例如，它发生在应用程序启动时，它执行大约 300 次写入，但是如果我通过暂停所有内容并使用 runBlocking 到 return 寻呼机来强制调用主线程，它确实可以工作，但我不不再出现错误，但它显然阻止了 ui，那么有没有办法使 switchmap 异步或使 searchAndFilterPokemonPager 方法 return 异步寻呼机？我知道第二个在技术上是可行的（return 来自异步）但也许协程有办法解决这个问题
感谢您的帮助

Answer 1

您可以使用 combineTuple (which is available as a library that I wrote for this specific purpose)（可选）

简化组合

之后，您可以使用 liveData { 协程构建器将执行移至后台线程

现在你的代码看起来像

val search: MutableLiveData<String> = getSearchState()
val filters: MutableLiveData<Set<String>> = getCurrentFiltersState()
val searchPokemon: LiveData<PagingData<PokemonWithTypesAndSpeciesForList>>

val isFiltersLayoutExpanded: MutableLiveData<Boolean> = getFiltersLayoutExpanded()

init {
    searchPokemon = combineTuple(search, filters).switchMap { (search, filters) -> 
        liveData {
            val search = search ?: return@liveData
            val filters = filters ?: return@liveData

            withContext(Dispatchers.IO) {
                emit(searchAndFilterPokemonPager(search, filters.toList()))
            }
        }
    }.distinctUntilChanged()
}

Android 后台线程上的实时数据转换

Android live data transformations on a background thread

android

android-room

android-livedata

android-paging

kotlin-coroutines