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在 RecyclerView 项目顺序发生更改后，我无法弄清楚我应该如何更新房间数据库中的数据。我应该如何根据用户操作更新 Room 中的 LiveData 项目？

使用 ItemTouchHelper.Callback 我设置了一个 onMove 回调，可以更改呈现给用户的项目顺序（拖放时），但是当我调用更新房间数据库中项目的顺序时，使用ViewModel 对象，然后用户一次只能移动一个项目。所以如果你拖动一个项目，它只会移动一个空格。

这是我在 ListAdapter 中定义的 onMove 函数，它为回调实现了 ItemTouchHelperAdapter。

override fun onMove(
        recyclerView: RecyclerView,
        fromViewHolder: RecyclerView.ViewHolder,
        toViewHolder: RecyclerView.ViewHolder
    ): Boolean {

        d(this.TAG, "swap viewHolders: " + fromViewHolder.adapterPosition + " to " + toViewHolder.adapterPosition)


        val workoutRoutine1 = workoutRoutines[fromViewHolder.adapterPosition]
        val workoutRoutine2 = workoutRoutines[toViewHolder.adapterPosition]

        workoutRoutine1.orderNumber = toViewHolder.adapterPosition.toLong()
        workoutRoutine2.orderNumber = fromViewHolder.adapterPosition.toLong()

        //this.workoutRoutinesViewModel.update(workoutRoutine1)
        //this.workoutRoutinesViewModel.update(workoutRoutine2)

        notifyItemMoved(fromViewHolder.adapterPosition, toViewHolder.adapterPosition)
        return true
    }

这是我的 DAO 对象

@Dao
interface WorkoutRoutineDAO {
    @Insert
    suspend fun insert(workoutRoutine: WorkoutRoutine)

    @Update(onConflict = OnConflictStrategy.REPLACE)
    suspend fun update(workoutRoutine: WorkoutRoutine)

    @Delete
    suspend fun delete(workoutRoutine: WorkoutRoutine)

    @Query("DELETE FROM workout_routine_table")
    fun deleteAll()

    @Query("SELECT * FROM workout_routine_table ORDER BY order_number ASC")
    fun getAllWorkoutRoutines(): LiveData<List<WorkoutRoutine>>

    @Query("SELECT COALESCE(MAX(order_number), -1) FROM workout_routine_table")
    fun getLargestOrderNumber(): Long
}

这是我的 RoomDatabase 对象

@Database(entities = [WorkoutRoutine::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun workoutRoutineDAO(): WorkoutRoutineDAO

    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null

        fun getDatabase(
            context: Context,
            scope: CoroutineScope
        ): AppDatabase {
            return INSTANCE ?: synchronized(this) {
                val instance =
                    Room.databaseBuilder(context.applicationContext, AppDatabase::class.java, "app_database")
                        .addCallback(WorkoutRoutineDatabaseCallback(scope))
                        .build()
                INSTANCE = instance
                instance
            }
        }
    }

    private class WorkoutRoutineDatabaseCallback(
        private val scope: CoroutineScope
    ) : RoomDatabase.Callback() {

    }
}

这是我实现的 ViewModel 对象。

class WorkoutRoutinesViewModel(application: Application) : AndroidViewModel(application) {
    private val workoutRoutinesRepository: WorkoutRoutineRepository

    val allWorkoutRoutines: LiveData<List<WorkoutRoutine>>

    init {
        // Get the DAO
        val workoutRoutineDAO = AppDatabase.getDatabase(application, viewModelScope).workoutRoutineDAO()
        // Build a new data repository for workout routines
        workoutRoutinesRepository = WorkoutRoutineRepository(workoutRoutineDAO)
        // Get a live view of the workout routines database
        allWorkoutRoutines = workoutRoutinesRepository.allRoutines
    }

    fun insert(workoutRoutine: WorkoutRoutine) = viewModelScope.launch(Dispatchers.IO) {
        workoutRoutinesRepository.insert(workoutRoutine)
    }

    fun update(workoutRoutine: WorkoutRoutine) = viewModelScope.launch(Dispatchers.IO) {
        workoutRoutinesRepository.update(workoutRoutine)
    }

    fun delete(workoutRoutine: WorkoutRoutine) = viewModelScope.launch(Dispatchers.IO) {
        workoutRoutinesRepository.delete(workoutRoutine)
    }
}

我希望用户能够移动项目 n 个空格，然后删除，并在用户删除项目时执行对 Room 数据库的更新，但是如果我将 Room 更新放在 onMove 方法中，用户只能移动项目一次。

当对象的顺序在回收站视图中发生变化时，我试图了解更新房间数据的正确方法。我试图让这些对象的顺序保持不变，即使用户退出应用程序或更改活动等。我应该如何使用 LiveData 将这些更改回显到 Room 数据库？

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1 回答 1

-2

您可以在 Udacity 上遵循本指南。它是免费的，由 Google 制作并使用 Kotlin。

于 2019-07-02T10:58:20.367 回答