如何从DataSnapshot插入数据到LiveData<List<Model>>？

Question

我需要将从 firebase 获得的数据插入到 LiveData，我不知道该怎么做

public LiveData<List<MedicationViewModel>> getAllMeds(){

        mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
             LiveData<List<MedicationViewModel>> medics; //Return this 
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        for(DataSnapshot ds : dataSnapshot.getChildren()) {

                            MedicationViewModel medic = ds.getValue(MedicationViewModel.class);
                            Log.d("TAG", medic.getMedName());
                             //TODO
                        }

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
    }

Answer 1

您应该将您的问题分成几个步骤：

Return 实时数据：如果你想要一个实时数据，那就意味着你想要有人观察它，所以我建议只拥有一个实时数据和 return 它到谁要这样观察

//=======Observer Activity/Fragment=============:
final Observer<List<MedicationViewModel>> medsObserver = new Observer<List<MedicationViewModel>>() {
    @Override
    public void onChanged(@Nullable final List<MedicationViewModel> medsList) {
        // Do what you need when the new list arrives
    }
};
yourObject.getAllMeds().observe(context, medsObserver) //setting the observer
//===============Your class============
private final MutableLiveData<List<MedicationViewModel>> allMedsLiveData = new MutableLiveData<>();
//...
public LiveData<List<MedicationViewModel>> getAllMeds(){
   return allMedsLiveData; //returning the liveData
}

来自firebase时填写数据：

//===============Your class============
private final MutableLiveData<List<MedicationViewModel>> allMedsLiveData = new MutableLiveData<>(); //the same one as the step 1
private final List<MedicationViewModel> allMedsList = new ArrayList<>();
//...
private void setUpListener() {
   mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot ds : dataSnapshot.getChildren()) {

                    MedicationViewModel medic = ds.getValue(MedicationViewModel.class);
                    Log.d("TAG", medic.getMedName());
                    allMedsList.add(medic); // or update if exists (just adding to keep things simple, but you get the idea)
                }
                allMedsLiveData.postValue(allMedsList) //Using postvalue here in case the DB is fetching data on a worker thread, as it should. This call will launch the "medsObserver" observer on the observer activity/fragment on step 1

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
 }

希望对你有用！

如何从DataSnapshot插入数据到LiveData<List<Model>>？

How to insert data from DataSnapshot to LiveData<List<Model>>?

lifecycle

android

firebase

firebase-realtime-database

android-livedata