android - 如何分离 firestore 监听器

Question

我是 FireStore 的新手。我创建了一个 ListenerRegistration 来更新我的 Recycler View。我知道我的实现可能并不完美，但每次我的 Activity 被销毁时，我的应用程序都会在此 Listener 内的行上抛出错误。我不知道为什么，但是 mt registration.remove() 在销毁之前或 finish() Activity 之后不起作用。有人可以帮忙吗？

public class MainActivity extends AppCompatActivity {

  private ListenerRegistration registration;
  private com.google.firebase.firestore.Query query;

  private void requestPacienteList(){

    FirebaseFirestore db = FirebaseFirestore.getInstance();
    progress.setVisibility(View.VISIBLE);
    query = db.collection("Hospital");
    registration = query.addSnapshotListener(new EventListener<QuerySnapshot>() {

        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            for(DocumentSnapshot documentSnapshot : documentSnapshots){

                if(documentSnapshot.get("nome").equals("Santa Clara")){

                    hospital = documentSnapshot.toObject(Hospital.class);
                    hospital.setHospitalDocumentKey(documentSnapshot.getId());
                    FirebaseFirestore db = FirebaseFirestore.getInstance();

                    db.collection("Hospital")
                            .document(hospital.getHospitalDocumentKey())
                            .collection("Pacientes")
                            .addSnapshotListener(new EventListener<QuerySnapshot>() {

                                 @Override
                                public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

                                    homeModelList.clear();
                                    for(DocumentSnapshot documentSnapshot : documentSnapshots){

                                        final Paciente paciente = documentSnapshot.toObject(Paciente.class);
                                        paciente.setPacienteKey(documentSnapshot.getId());
                                        FirebaseFirestore db = FirebaseFirestore.getInstance();
                                        db.collection("Pessoa")
                                                .document(paciente.getProfissionalResponsavel())
                                                .addSnapshotListener(new EventListener<DocumentSnapshot>() {

                                                    @Override
                                                    public void onEvent(DocumentSnapshot documentSnapshot, FirebaseFirestoreException e) {

                                                        Profissional profissional = documentSnapshot.toObject(Profissional.class);
                                                        int[] covers = new int[]{R.drawable.ic_person_black};
                                                        HomeModel p = new HomeModel(paciente.getNome()+" "+paciente.getSobrenome(),paciente.getBox(),paciente.getLeito(),
                                                        covers[0],profissional.getNome()+ " "+profissional.getSobrenome(),paciente.getPacienteKey());
                                                        homeModelList.add(p);
                                                        homeAdapter.notifyDataSetChanged();
                                                        prepareListaPacientes();
                                                    }
                                        });
                                    }
                                }
                            });
                    }
            }
        }
    });

    switch (id){

        case R.id.logout:

            if(FirebaseAuth.getInstance().getCurrentUser()!=null)
                FirebaseAuth.getInstance().signOut();

            Intent it = new Intent(HomeActivity.this, MainActivity.class);
            startActivity(it);

            if(registration!=null)
                registration.remove();

            finish();

            drawerLayout.closeDrawers();
            break;
    }
  }

}

My onDestroy method:

@Override
protected void onDestroy() {
    super.onDestroy();
    registration.remove();
}

When I remove this if:

if(FirebaseAuth.getInstance().getCurrentUser()!=null)
    FirebaseAuth.getInstance().signOut();

我的问题解决了。但如果我不这样做，我会收到以下错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object com.google.firebase.firestore.DocumentSnapshot.toObject(java.lang.Class)' on a null object reference at santauti.app.Activities.Home.HomeActivity$4$1$1.onEvent(HomeActivity.java:200) at santauti.app.Activities.Home.HomeActivity$4$1$1.onEvent(HomeActivity.java:197) at com.google.firebase.firestore.DocumentReference.zza(Unknown Source) at com.google.firebase.firestore.zzd.onEvent(Unknown Source) at com.google.android.gms.internal.zzejz.zza(Unknown Source) at com.google.android.gms.internal.zzeka.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

当你use addSnapshotListener您附加一个监听器，该监听器会被要求进行任何更改。显然你必须 detach those listeners在 Activity 被销毁之前。另一种选择是 add the activity to your call to addSnapshotListener :

 db.collection("Pessoa").document(paciente.getProfissionalResponsavel())
   .addSnapshotListener(MainActivity.this, new EventListener<DocumentSnapshot>() {

您需要更新 MainActivity.this 以匹配您的代码。

通过传入activity，Firestore可以在activity停止时自动清理监听器。

另一种选择是使用 get()获取那些嵌套的文档，它只读取文档一次。由于它只读取一次，因此没有需要清理的监听器。