从数据库中导入的数据未设置

Question

我正在制作与图像类似的屏幕。

提前从Room db中获取数据集，并为每个选项卡设置数据集。

每个选项卡为fragment，并在recyclerview中显示数据。

每个选项卡都包含不同的数据，因此我将选项卡设置为livedata in viewModel并观察它。

因此，每当选项卡更改时，目标是从数据库中获取每个选项卡的数据，并在recyclerview中设置它。

但是，即使我导入数据，也没有在recyclerview中设置它。

我认为即使在调试数据时，数据也很顺利。

这不是适配器问题。

我想念什么？

---

Workoutlist

@Entity
data class WorkoutList(
    @PrimaryKey(autoGenerate = true)
    val id: Long = 0,
    val chest: List<String>,
    val back: List<String>,
    val leg: List<String>,
    val shoulder: List<String>,
    val biceps: List<String>,
    val triceps: List<String>,
    val abs: List<String>
)

ViewModel

class WorkoutListViewModel(application: Application) : AndroidViewModel(application){
    private var _part :MutableLiveData<BodyPart> = MutableLiveData()
    private var result : List<String> = listOf()

    private val workoutDao = WorkoutListDatabase.getDatabase(application).workoutListDao()
    private val workoutListRepo = WorkoutListRepository(workoutDao)
    
    val part = _part

    fun setList(part : BodyPart) : List<String> {
        _part.value = part

        viewModelScope.launch(Dispatchers.IO){
            result = workoutListRepo.getWorkoutList(part)
        }
        return result
    }
}

存储库

class WorkoutListRepository(private val workoutListDao: WorkoutListDao) {
    suspend fun getWorkoutList(part: BodyPart) : List<String> {
        val partList = workoutListDao.getWorkoutList()

        return when(part) {
            is BodyPart.Chest -> partList.chest
            is BodyPart.Back -> partList.back
            is BodyPart.Leg -> partList.leg
            is BodyPart.Shoulder -> partList.shoulder
            is BodyPart.Biceps -> partList.biceps
            is BodyPart.Triceps -> partList.triceps
            is BodyPart.Abs -> partList.abs
        }
    }
}

fragment

class WorkoutListTabPageFragment : Fragment() {
    private var _binding : FragmentWorkoutListTabPageBinding? = null
    private val binding get() = _binding!!
    private lateinit var adapter: WorkoutListAdapter
    private lateinit var part: BodyPart

    private val viewModel: WorkoutListViewModel by viewModels()

    companion object {
        @JvmStatic
        fun newInstance(part: BodyPart) =
            WorkoutListTabPageFragment().apply {
                arguments = Bundle().apply {
                    putParcelable("part", part)
                }
            }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let { bundle ->
            part = bundle.getParcelable("part") ?: throw NullPointerException("No BodyPart Object")
        }
    }

    override fun onCreateView(inflater: LayoutInflater,
                              container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        _binding = FragmentWorkoutListTabPageBinding.inflate(inflater, container, false)
        binding.apply {
            adapter = WorkoutListAdapter()
            rv.adapter = adapter
        }

        val result = viewModel.setList(part)

        // Set data whenever tab changes
        viewModel.part.observe(viewLifecycleOwner) { _ ->
//            val result = viewModel.setList(part)
            adapter.addItems(result)
        }

        return binding.root
    }
}     viewModel.part.observe(viewLifecycleOwner) { _ ->
            adapter.addItems(result)
        }

        return binding.root
    }
}

Answer 1

您看到的问题是，在setList中，您在IO线程上启动异步的coroutine以获取列表，但是您实际上并没有等待该coroutine运行，而只需立即返回空列表。

修复的一种方法是观察一个包含列表的寿命对象，而不是观察零件。然后，当异步任务完成时
您可以将检索到的数据发布到该Livedata。然后在视图模型中看起来像这样，

class WorkoutListViewModel(application: Application) : AndroidViewModel(application) {

    private val _list = MutableLiveData<List<String>>()
    val list: LiveData<List<String>>
        get() = _list

    // "part" does not need to be a member of the view model 
    // based on the code you shared, but if you wanted it
    // to be you could do it like this, then
    // call "viewModel.part = part" in "onCreateView". It does not need
    // to be LiveData if it's only ever set from the Fragment directly.
    //var part: BodyPart = BodyPart.Chest
    
       
    // calling getList STARTS the async process, but the function
    // does not return anything
    fun getList(part: BodyPart) {
        viewModelScope.launch(Dispatchers.IO){
            val result = workoutListRepo.getWorkoutList(part)
            _list.postValue(result)
        }
    }
}

然后在片段increateview中观察列表，当值更改时，您将它们添加到适配器中。如果值可能会发生多次变化，则可能需要清除适配器，然后再添加观察者内部的项目。

override fun onCreateView(inflater: LayoutInflater,
                          container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {
    //...

    // Set data whenever new data is posted
    viewModel.list.observe(viewLifecycleOwner) { result ->
        adapter.addItems(result)
    }
    
    // Start the async process of retrieving the list, when retrieved
    // it will be posted to the live data and trigger the observer
    viewModel.getList(part)

    return binding.root
}
    

note ：文档当前仅建议在increateview中仅夸大视图并在<代码中进行所有其他设置和初始化> onviewCreated - 我将其保留在问题中以保持一致性。