Android:从Firebase数据库获取带有两个ValueEventListener的数据(在Arraylist过期之前设置适配器) [英] Android: getting datas with two ValueEventListener from firebase database (setting adapter before Arraylist Expires)

问题描述

我正在开发一个应用程序，并且在数据库中有像医生和病人这样的用户.患者数据中可能有医生userId，而医生数据中可能有患者userId.因为在应用程序中，医生将看到有关他/她的患者的一些信息.我开发了这段代码，但是在设置适配器之前无法将患者信息添加到Arraylists中.这是我的代码:

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) {
        }
    });

当我调试代码时，看到的是，设置适配器后，患者信息会添加到列表中.所以我的RecyclerView是空的.我该如何解决这个问题?

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?

推荐答案

要解决此问题，请移动以下代码行:

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()));

在第二个onDataChange()方法中，如下所示:

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) {}
});

之所以发生这种情况，是因为onDataChange()具有异步行为.请在 此处 模式详细信息.

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

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