Question

我正在尝试检索数据库值，但是使用uID提取的节点/子节点中的数据为空。这是我的代码-

    Intent intent = getIntent();
            Bundle extras = intent.getExtras();
            currentUser = extras.getString("currentUser");
            selectedUser = extras.getString("selectedUser");
            uID = extras.getString("uID");
    mFirebaseDatabase = FirebaseDatabase.getInstance();


mDbReference = FirebaseDatabase.getInstance().getReference();
    final DatabaseReference uidRef = mDbReference.child("users").child(uID);

    ValueEventListener valueEventListener = new ValueEventListener() {


@Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                ChatMessageModel chatMessageModel = ds.getValue(ChatMessageModel.class);
                Log.d(TAG, "onDataChange: " + uidRef);
                Log.d("users:: ", chatMessageModel.getMsgContent());
                    messageList.add(chatMessageModel);
                    for (int i = 0; i < messageList.size(); i++) {
                        Log.d(TAG, "All received messages : " + messageList.get(i).getMsgContent());

                    }
                }
                chatAppMsgAdapter.notifyDataSetChanged();
                //Do what you need to do with the list.
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.d(TAG, databaseError.getMessage());
            }
        };
        uidRef.addListenerForSingleValueEvent(valueEventListener);

//这是我的数据库
u0TddklO8BXKCRHp4UFXEvmPS1H3：null // u0TddklO8BXKCRHp4UFXEvmPS1H3是uid。 uid是当前用户。

Answer 1

假设user1是第一个用户的对应uid，要使所有ChatMessageModel对象在您的user1节点下，请使用以下代码：< / p>

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference uidRef = rootRef.child("users").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        ArrayList<ChatMessageModel> messageList = new ArrayList<>();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            ChatMessageModel chatMessageModel = ds.getValue(ChatMessageModel.class);
            Log.d("users:: ", chatMessageModel.getMsgContent());
            messageList.add(chatMessageModel);
        }

        //Do what you need to do with the list.
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage());
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

Answer 2

首先尝试通过将Firebase数据库规则设置为以下内容来调试应用程序-
```
{
   "rules": {
   ".read": true,
   ".write": true
   }
} 
```

如果仍然无效，请尝试执行此操作-

private FirebaseDatabase database;
private DatabaseReference databaseRef;

database = FirebaseDatabase.getInstance();
databaseRef = database.getReference("users");

databaseRef.addValueEventListener(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot dataSnapshot) {
         for(DataSnapshot snapshot:dataSnapshot.getChildren()){
            Log.d("Output Key", snapshot.getKey());
            Log.d("Output Value", snapshot.getValue().toString());
        }
     }
     @Override
     public void onCancelled(DatabaseError databaseError) {

     }
});

检索Firebase数据库时，子节点值为空

2 个答案: