如何将数据从 DataSnapshot 插入到 LiveData<List<Model>>？

问题描述

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) {

                    }
                });
    }

解决方法

你应该把你的问题分成几个步骤：

1. 返回实时数据：如果你想要一个实时数据，这意味着你希望有人观察它，所以我建议只拥有一个实时数据并将它返回给任何想要观察的人

   //=======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
   }
   

2. 填充来自 firebase 的数据：

   //===============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) {
   
               }
           });
    }
   

希望它对你有用！