I am trying to retrieve data from Firebase Realtime Database and add this data to a listview. When I call push() firebase generates two children (one inside the other) with the same unique key. This is the structure of my database:

database

That is how I save the data:

RunningSession runningSession = new RunningSession(date, activityTime, pace, timeElapsed,
                                finalDistance, image, tipe);

DatabaseReference reference = databaseReference.child("users").child(userUid).child("activities").push();

Map<String, Object> map = new HashMap<>();
map.put(reference.getKey(),runningSession);
reference.updateChildren(map);

This is how i retrieve the data (results in a null pointer exception):

DatabaseReference reference = databaseReference.child("users").child(userId).child("activities");
reference.addValueEventListener(new ValueEventListener() {
       @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
             list.clear();
             for (DataSnapshot snpshot : snapshot.getChildren()) {
                    RunningSession run = snpshot.getValue(RunningSession.class);
                    list.add(run);
             }
        }

       @Override
        public void onCancelled(@NonNull DatabaseError error) {
        }
   });

   ListViewAdapter adapter = new ListViewAdapter(this, list);
   ListView activityItems = (ListView) findViewById(R.id.activityList);
   activityItems.setAdapter(adapter);

CodePudding user response：

You are getting duplicate push IDs because you are adding them twice to your reference. If you only need one, then simply use the following lines of code:

RunningSession runningSession = new RunningSession(date, activityTime, pace, timeElapsed, finalDistance, image, tipe);
DatabaseReference reference = databaseReference.child("users").child(userUid).child("activities");
String pushedId = reference.push().getKey();
reference.child(pushedId).setValue(runningSession);

The code for reading that may remain unchanged.