Firebase Value Event Listener

问题

I want to read the values from Firebase Database and show in a ListView. But something gone wrong. It's not giving correct values. Here is the code:

Java

    final FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference reference = database.getReference("Stats").child(ders);

    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            stats.put(dataSnapshot.getKey(), dataSnapshot.getValue().toString());
            StatsAdapter adapter = new StatsAdapter(stats);
            listView.setAdapter(adapter);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(getApplicationContext(), databaseError.getMessage(), Toast.LENGTH_SHORT).show();
            startActivity(new Intent(StatsActivity.this, DerslerListActivity.class));
        }
    });

JSON

"Stats" : {
"Matematik" : {
  "ahmetozrahat25" : "50",
  "nihatkeklik" : 50
},
"Türkçe" : {
  "abdullah" : 98,
  "ahmetozrahat25" : "0",
  "banuozrht" : 95,
  "nihatkeklik" : 60
}
}

Result is Matematik, {ahmetozrahat=50, nihatkeklik=50} but I want: ahmetozrahat25: 50, nihatkeklik: 50. What should I do?

回答1:

Egek92's answer is right. And I think I know why it doesn't provide data you want. Maybe with this following code, you will:

DatabaseReference reference = database.getReference("Stats").child("Matematik");
reference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // dataSnapshot value will be Matematik, {ahmetozrahat=50, nihatkeklik=50}
        // because it is indeed the value we need

        // But you want key value pair to be added to your stats
        // So we can just loop through the values

        for (DataSnapshot childSnapshot : dataSnapshot.getChildren()) {
            stats.put(childSnapshot.getKey(), childSnapshot.getValue().toString());
        }
        StatsAdapter adapter = new StatsAdapter(stats);
        listView.setAdapter(adapter);
    }
    ...
}

Hope this helps

回答2:

Try:

DatabaseReference reference = database.getReference("Stats").child("Matematik");

来源：https://stackoverflow.com/questions/42986449/firebase-value-event-listener