我正在尝试使用Paging 3
库来获取Flow<PagingData<Scan>>
from Room
,然后检查回收器视图中是否选择了项目,因此我将此类映射到另一个名为的类ScanMapper
。为了实现此映射,每当用户将某个项目标记为选定时,我都会更新Map
里面一个MutableStateFlow<Map<Int, State>>
。这里的Map
查找一个Index(Int)
得到State
, State
只是一个enum
代表状态的类UNINITIALISED
, USELECTED
and SELECTED
.
我将 Map 的值设置为StateFlow<Map<Int,State>>
。问题是,我正在尝试结合Flow<PagingData<Scan>>
与StateFlow<Map<Int,State>>
为了也通过State
作为参数ScanMapper
从此上课State
取自StateFlow<Map<Int,State>>
并且不是原件的一部分Scan
班级。但是PagingDataAdapter
似乎总是得到State UNINITIALISED
尽管当我将项目标记为在项目上单击时使用markSelected(scanId: Int)
功能。
请告诉我我在这里缺少什么。
UPDATE
我能够通过使用实现我想要的功能Flow<List<Scan>>
并删除使用Paging 3
使用回收器适配器的库DiffUtils
。尽管这不是实际的解决方案,因为它消除了pagination using paging 3
库,但以下更改允许我执行项目选择:
更新了刀
@Query("SELECT * FROM scan ORDER BY timeOfStorage DESC")
fun getAllScansList(): Flow<List<Scan>>
ViewModel 中的更新功能
fun getData(context: Context): Flow<List<ScanMapper>> {
val dao = ScanDatabase.invoke(context).getScanDao()
return combine(
dao.getAllScansList(),
myMap
) { scan, stateMap ->
scan.map {
it.toScanMapper(stateMap[it.id] ?: State.UNKNOWN)
}
}.flatMapLatest {
flow {
emit(it)
}
}
}
更新了片段代码
mainViewModel.getData(requireContext()).collect {
adapter.asyncListDiffer.submitList(it as MutableList)
}
原始问题
我的扫描课程:
@Entity(tableName = "scan")
@Parcelize
data class Scan (
@PrimaryKey(autoGenerate = true)
var id: Int = 0,
val name: String,
val recognisedText: String,
val timeOfStorage: Long,
val filename: String
): Parcelable {
}
我的 ScanMapper 类:
data class ScanMapper(
val id: Int,
val name: String,
val recognisedText: String,
val timeOfStorage: Long,
val filename: String,
val isSelected: State
)
enum class State{
UNINITIALISED,
SELECTED,
UNSELECTED,
UNKNOWN
}
Scan 到 ScanMapper 的转换器,反之亦然
fun ScanMapper.mapToScan() =
Scan(
id = id,
name = name,
recognisedText = recognisedText,
timeOfStorage = timeOfStorage,
filename = filename
)
fun Scan.toScanMapper(isSelected: State) =
ScanMapper(
id = id,
name = name,
recognisedText = recognisedText,
timeOfStorage = timeOfStorage,
filename = filename,
isSelected = isSelected
)
Dao 中的我的 PagingSource
@Query("SELECT * FROM scan ORDER BY timeOfStorage DESC")
fun getAllScans(): PagingSource<Int,Scan>
@Query("SELECT id FROM scan")
fun getAllIds(): List<Int>
使用 getScansFlow() 获取流量
fun getScansFlow(context: Context): Flow<PagingData<Scan>> {
val scanDao = ScanDatabase.invoke(context).getScanDao()
return Pager(
config = PagingConfig(
pageSize = 10,
maxSize = 30,
enablePlaceholders = false
),
pagingSourceFactory = { scanDao.getAllScans() }
).flow.cachedIn(viewModelScope)
}
初始化房间中存在的 ID 的地图
fun initList() =
viewModelScope.launch {
var idList: List<Int> = listOf()
withContext(Dispatchers.IO) {
val task = async {
return@async ScanDatabase.invoke(context).getScanDao().getAllIds()
}
idList = task.await()
}
val map = _myMap.value.toMutableMap()
for (id in idList) {
map[id] = State.UNINITIALISED
}
_myMap.value = map
}
ViewModel 中获取流程并将其组合的函数
fun getScansSyncFlow(context: Context) {
viewModelScope.launch {
combine(
getScansFlow(context),
myMap
) { scan, stateMap ->
scan.map {
it.toScanMapper(stateMap[it.id] ?: State.UNKNOWN)
}
}.collect{
_myFlow.emit(it)
}
}
}
myFlow
is a StateFlow<PagingData<ScanMapper>?>
.
这就是我更新的方式Map
当用户在 recyclerview 中选择某个项目时。
fun markSelected(scanId: Int) {
val map = _myMap.value.toMutableMap()
map[scanId] = State.SELECTED
_myMap.value = map
}
那我就收集这个myFlow
in my fragment
像这样:
lifecycleScope.launchWhenStarted {
mainViewModel.getScansSyncFlow(requireContext())
mainViewModel.myFlow.collect { data ->
data?.let {
adapter.submitData(it)
}
}
}