Android 如何从Room数据库构建流，同时处理之前的值

我对Android开发非常陌生.

我有一个房间结果数据库:

@Entity(tableName = "results")
data class Result(
    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,
    val result : Float,
    val date : String
)

@Database(
    entities = [Result::class],
    version = 1,
    exportSchema = false
)
abstract class ResultDatabase : RoomDatabase() {
    abstract fun resultDao() : ResultDao

    companion object {
        @Volatile
        private var Instance : ResultDatabase? = null

        fun getDatabase(context : Context) : ResultDatabase {
            return Instance ?: synchronized(this) {
                Room.databaseBuilder(context, ResultDatabase::class.java, "result_database")
                    .fallbackToDestructiveMigration()
                    .build()
                    .also { Instance = it }
            }
        }
    }
}

有一个ASO

@Dao
interface ResultDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insert(result : Result)

    @Update
    suspend fun update(result : Result)

    @Delete
    suspend fun delete(result : Result)

    @Query("SELECT * FROM results WHERE id = :id")
    fun getResult(id : Int) : Flow<Result>

    @Query("SELECT * FROM results ORDER BY date ASC")
    fun getAllResults() : Flow<List<Result>>
}

以及存储库

class ResultRepository(private val resultDao : ResultDao) {

    fun getAllResults(): Flow<List<Result>> = resultDao.getAllResults()

    suspend fun getResultsSmoothed(numSteps : Int) : List<Result> {

        var allResults : List<Result> = listOf()
        getAllResults().collect { result -> allResults = allResults + result }

        val minDate = LocalDateTime.parse(allResults.first().date)
        val maxDate = LocalDateTime.parse(allResults.last().date)

        val period = Duration.between(minDate, maxDate)

        var step = period.seconds / numSteps

        var hundredResults = listOf<Result>()

        var nextDate = minDate

        for (i in 0..numSteps) {

            val resultPrior = allResults.fold(allResults.first()) { acc: Result, r ->
                val rd = LocalDateTime.parse(r.date)
                if (rd <= nextDate && (rd > LocalDateTime.parse(acc.date))) r
                else acc
            }

            val resultAfter = allResults.fold(allResults.last()) { acc: Result, r ->
                val rd = LocalDateTime.parse(r.date)
                if (rd > nextDate && (rd <= LocalDateTime.parse(acc.date))) r
                else acc
            }

            if (resultAfter == resultPrior) {
                val newResult = Result(date = nextDate.toString(), result = resultPrior.result)
                hundredResults = hundredResults + newResult
            } else {

                val resultPriorDate = LocalDateTime.parse(resultPrior.date)
                val resultAfterDate = LocalDateTime.parse(resultAfter.date)
                val periodBetween = Duration.between(resultPriorDate, resultAfterDate)

                val periodOver = Duration.between(resultPriorDate, nextDate)

                val percentageOver =
                    periodOver.seconds.toDouble() / periodBetween.seconds.toDouble();

                val resultDifference = resultAfter.result - resultPrior.result;
                val increaseToPriorAmount = resultDifference.toDouble() * percentageOver;

                val stepResult = resultPrior.result + increaseToPriorAmount;

                val newResult = Result(date = nextDate.toString(), result = stepResult.toFloat())
                hundredResults = hundredResults + newResult
            }
            nextDate = nextDate.plusSeconds(step)
        }

        return hundredResults
    }

    suspend fun getResultLabels(numLabels : Int) : List<String> {

        var allResults : List<Result> = listOf()
        getAllResults().collect { result -> allResults = allResults + result }

        val minDate = LocalDateTime.parse(allResults.first().date)
        val maxDate = LocalDateTime.parse(allResults.last().date)

        val period = Duration.between(minDate, maxDate)

        val step = period.seconds / numLabels

        var dateLabels = listOf<String>()

        var nextDate = minDate

        for (i in 0..numLabels) {
            val formatter = DateTimeFormatter.ofPattern("d MMM yy")
            dateLabels = dateLabels + nextDate.format(formatter)
            nextDate = nextDate.plusSeconds(step)
        }

        return dateLabels
    }

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun insertResult(result : Result) {
        resultDao.insert(result)
    }

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun updateResult(result : Result) {
        resultDao.update(result)
    }

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun deleteResult(result : Result) {
        resultDao.delete(result)
    }
}

两个函数getResultLabels和getResultsSmoothed正在处理数据库中的一些值并返回内容.我将其放在这里的原因是将其提供给视图模型，因为我已经明白我不应该在我的组合中进行这种处理.

然后我的视图模型

class ResultViewModel(private val repository: ResultRepository) : ViewModel() {

    val allResults = repository.getAllResults()

    fun getSmoothedResults(num : Int) : Flow<List<Result>> {
        return flow {
            val results = repository.getResultsSmoothed(num)
            Log.d("ME vm", results.toString())
            emit(results)
        }
    }

    fun getResultLabels(num : Int) : Flow<List<String>> {
        return flow { emit(repository.getResultLabels(num)) }
    }

    fun update(result : Result) = viewModelScope.launch {
        repository.updateResult(result)
    }

    fun delete(result : Result) = viewModelScope.launch {
        repository.deleteResult(result)
    }

    fun insert(result : Result) = viewModelScope.launch {
        repository.insertResult(result)
    }
}

class ResultViewModelFactory(private val repository: ResultRepository) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass : Class<T>) : T {
        if(modelClass.isAssignableFrom(ResultViewModel::class.java)) {
            @Suppress("UNCHECKED_CAST")
            return ResultViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

我试图做的是将这些List放入Flow中，以便使用它们的组合将自动更新.

例如:

@Composable
fun Metrics(resultViewModel: ResultViewModel,
            resultList : List<Result>?) {

    if(resultList.isNullOrEmpty())
        return

    var dateLabels = resultViewModel.getResultLabels(5).collectAsState(initial = listOf())

    var hundredResults = resultViewModel.getSmoothedResults(100).collectAsState(
        initial = listOf()
    )

    Log.d("memememe", hundredResults.value.toString())

    Column()
    {
        LineChart(
            modifier = Modifier
                .fillMaxWidth()
                .height(300.dp)
                .padding(top = 12.dp, end = 12.dp),
            linesChartData = listOf(LineChartData(
                lineDrawer = SolidLineDrawer(color = MaterialTheme.colorScheme.onBackground),
                points = hundredResults.value.map {
                    LineChartData.Point(it.result, it.id.toString())
                })),
            animation = simpleChartAnimation(),
            pointDrawer = com.github.tehras.charts.line.renderer.point.NoPointDrawer,
            labels = dateLabels.value,
            xAxisDrawer = SimpleXAxisDrawer(
                axisLineThickness = 1.dp,
                axisLineColor = MaterialTheme.colorScheme.onBackground,
                labelTextColor = MaterialTheme.colorScheme.onBackground
            ),
            yAxisDrawer = SimpleYAxisDrawer(
                axisLineThickness = 1.dp,
                axisLineColor = MaterialTheme.colorScheme.onBackground,
                labelTextColor = MaterialTheme.colorScheme.onBackground
            )
        )
        DataTable(
            modifier = Modifier.fillMaxWidth(),
            columns = listOf(
                DataColumn(
                    width = TableColumnWidth.Fixed(60.dp)
                ) {
                    Text("")
                },
                DataColumn {
                    Text("Date")
                },
                DataColumn {
                    Text("Result")
                }
            )
        ) {
            resultList.forEach { r ->
                row {
                    cell {
                        IconButton(onClick = { resultViewModel.delete(r) }) {
                            Icon(Icons.TwoTone.Delete, "Delete result")
                        }
                    }
                    cell {
                        Text(
                            text = LocalDateTime.parse(r.date)
                                .format(DateTimeFormatter.ofPattern("dd MMM yyyy"))
                        )
                    }
                    cell {
                        Text("${r.result}")
                    }
                }
            }
        }
    }
}

然而，我的日志(log)呼叫有一个空列表.我可能完全错误地处理这个问题，但我不确定.我对协程和状态的使用以及它们如何相互作用有点困惑.