从firebase实时数据库中获取指定的子项

Question

我试图Messages/child在基础上检索排序time。我可以访问Messages/child。我找不到任何有用的解决方案。请帮我解决这个问题。我目前的代码是：FirebaseDatabase.getInstance()     .getReference()     .child("Messages")     .child(FirebaseAuth.getInstance().getCurrentUser().getUid())     .addChildEventListener(new ChildEventListener() {           @Override           public void onChildAdded(@NonNull DataSnapshot dataSnapshot,  @Nullable, String s) {               Log.d("children",dataSnapshot.getKey());               users_list.add(dataSnapshot.getKey());           }

Answer 1

你可以这样做： -

mChatReference = FirebaseDatabase.getInstance().getReference("Messages")
                .child(FirebaseAuth.getInstance().getCurrentUser().getUid());
        Query query = mChatReference.orderByChild("time");
        query.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                   Log.d("children",dataSnapshot.getKey());
                users_list.add(dataSnapshot.getKey());            
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });

Answer 2

试试这个..

DocumentReference docRef = FirebaseFirestore.getInstance().collection(YOUR_COLLECTION).document(FirebaseAuth.getInstance().
getCurrentUser().getUid());docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
        if (task.isSuccessful()) {
            DocumentSnapshot document = task.getResult();
            if (document.exists()) {
                if (document.contains("message")) {
                        String message=document.get("message").toString());
                    }
                //add other information to your user_list
            }
        }
    }});