Android: getting datas with two ValueEventListener from firebase database (setting adapter before Arraylist Expires)

Question

I'm developing an app and in database there are users like doctor and patient. There may be doctors userId in patient datas and patient userId in doctor datas. Because in app doctor will see some information about his/her patient. I develop this chunk of codes, but I could not add patient informations to Arraylists before setting adapter. Here is my codes:

  myRef.child("users")
            .child(firebaseUser.getUid()).child("patients").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                for(DataSnapshot ds: dataSnapshot.getChildren()){
                    AddingPatients addingpatient = ds.getValue(AddingPatients.class);

                    if(addingpatient.getConfirm().equals("yes")){

                        myref.child("users").child(addingpatient.getUserId()).addValueEventListener(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                if (dataSnapshot.exists()) {
                                    Users patient = dataSnapshot.getValue(Users.class);

                                    name.add(patient.getName()+" "+patient.getSurname());

                                    sicks.add(patient.getSicks());
                                    patientuid.add(patient.getUserId());
                                }

                            }

                            @Override
                            public void onCancelled(DatabaseError error) {
                            }
                        });
                    }
                }

            PatientSelectionAdapter adapter= new PatientSelectionAdapter(getContext(),name,sicks,hastauid);
            rv.setAdapter(adapter);
            rv.setLayoutManager(new LinearLayoutManager(getContext()));

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
        }
    });

When I debug codes I saw that, patient information is adding to lists after setting adapter. So my RecyclerView is empty. How can i fix that problem?

score 2 · Accepted Answer · answered Sep 29 '18 at 14:05

2

To solve this, please move the following lines of code:

PatientSelectionAdapter adapter= new PatientSelectionAdapter(getContext(),name,sicks,hastauid);
rv.setAdapter(adapter);
rv.setLayoutManager(new LinearLayoutManager(getContext()));

Inside the second onDataChange() method like this:

myref.child("users").child(addingpatient.getUserId()).addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.exists()) {
            Users patient = dataSnapshot.getValue(Users.class);

            name.add(patient.getName()+" "+patient.getSurname());

            sicks.add(patient.getSicks());
            patientuid.add(patient.getUserId());
        }
        PatientSelectionAdapter adapter= new PatientSelectionAdapter(getContext(),name,sicks,hastauid);
        rv.setAdapter(adapter);
        rv.setLayoutManager(new LinearLayoutManager(getContext()));
    }

    @Override
    public void onCancelled(DatabaseError error) {}
});

This is happening because onDataChange() has an asynchronous behavior. Please see here mode details.

answered Sep 29 '18 at 14:05

Alex Mamo

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I've tried it but it's a problem: the patient is taking photos of the wound and updating the total number of photos after each photo. When this is the way the new photo is added, 4 data of the same patient is displayed in the recycler view. – Kemal Aydeniz Sep 29 '18 at 14:14
How to fix that problem Alex? – Kemal Aydeniz Sep 29 '18 at 14:17
Let's stick to one question at a time. Using my above code, is your `RecyclerView` still empty? – Alex Mamo Sep 29 '18 at 14:29
No, code is working. There are patients in RecyclerView. – Kemal Aydeniz Sep 29 '18 at 14:30
Can we pass second question or post a new topic? – Kemal Aydeniz Sep 29 '18 at 14:33
In order to follow the rules of this comunity, please post another fresh question, so me and other users can help you. – Alex Mamo Sep 29 '18 at 14:39

score 0 · Answer 2 · answered Sep 29 '18 at 17:40

You need to:

Move the following line to top outer onDataChange().

PatientSelectionAdapter adapter= new PatientSelectionAdapter(getContext(),name,sicks,hastauid);

Insert following line before returning from inner onDataChange()
```
adapter.notifyDataSetChanged();
```

Android: getting datas with two ValueEventListener from firebase database (setting adapter before Arraylist Expires)

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