Andriod返回Null应用失败的FireBase Asyc调用失败

Question

Firebase异步调用返回null

尝试添加无法正常运行的Log.d。 AnchorId是类级别的对象

String getValueFromDataBase(String shortCode){

     databaseReference.child("CloudAnchorData").addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                    Log.d(TAG, "step 2" + anchorId.toString());
                    AnchorData usersData = dataSnapshot.child("CloudAnchorData").child(shortCode).getValue(AnchorData.class);
                    Log.d(TAG, "inside method" +usersData.toString());
                    if(usersData.getShortCode().equals(shortCode)){
                        anchorId = usersData.getCloudAnchorId().toString();
                        Log.d(TAG, anchorId.toString());
                        return;
                    }
                 Log.d(TAG, anchorId.toString());
                Log.d("TAG", "Inside onDataChange() method!");
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {}
        });
        Log.d("TAG", "After attaching the listener!" +anchorId.toString());
        return anchorId;
    }

应返回值，而不是null