在 Worker 上更改数据库后，LiveData 未更新

Question

I have a Worker that send some images to a server. When the Worker starts, I need to change my view status to "In progress" and when the Worker finish, I need to change my view status to "Finished". But, when I update the Room Database inside the Worker, my view can't understand that the database has changed and the LiveData is not notified. If I make the same call before the Worker starts, the LiveData understand the changes and updates my View. The problem that I have is that my view doesn't know exactly what item of the recyclerview it should update, so I can't observe the Worker on the View. I need to make this update inside the Worker.

--- Updated with code ---

Fragment

viewModel.shortHistoryViewModelList.observe(viewLifecycleOwner, Observer { 
        binding.viewModel = viewModel
        adapter.replace(shortHistories)
        binding.executePendingBindings()
        scrollToItem(shortHistories)
})

ViewModel

private val results: MediatorLiveData<List<ShortHistory>> = MediatorLiveData()
init {
    this.state.value = NetworkStateEnum.NONE
    results.addSource(repository.get()) {
        results.postValue(it)
    }
}

val shortHistoryViewModelList: LiveData<List<ShortHistoryViewModel>> =
        Transformations.switchMap(results) { shortHistories ->
            val mutableLiveData: MutableLiveData<List<ShortHistoryViewModel>> = MutableLiveData()
            val list = ArrayList<ShortHistoryViewModel>()

            for (shortHistory in shortHistories) {
                list.add(ShortHistoryViewModel(shortHistory))
            }
            mutableLiveData.value = list
            mutableLiveData
        }

Worker

val shortHistory = shortHistoryRepository.get(shipmentId)
shortHistory.digitalReceipt = shortHistory.digitalReceipt?.copy(status = DigitalReceiptStatusEnum.Sending.value)
shortHistoryRepository.insert(shortHistory)

Answer 1

UI can only be updated from the UI Thread ( which is also the main Thread ) and not in any other thread like the Worker you are using. Use runOnUiThread(Runnable action) method inside your Worker thread to run any code that has to do with updating the UI.

Answer 2

Not sure what problem you are having since you are refusing to post relevant code but I suspect that you are changing the livedata inside a worker thread. If that is the case, you need to notify the livedata that it has changed by calling its postValue() method.

Answer 3

I went through the same problem.

I found that If we run room-db @RawQuery, then liveData or kotlin flow don't get updated.

So, we have to use normal @Update query instead of @RawQuery.