如何从Firebase数据库接收两个字符串？

Question

在本课程中，我尝试更改评分。我应该收到两个变量，但我不能这样做。检查我的ChildChanged监听器，错误就在附近。

这是我的数据库：

这是我的代码：

public class MainActivity extends AppCompatActivity {
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private Button btn;
String TAG = "first";
 float r,n,r1,r2,rat; String LEC_ID = "5058586";

private DatabaseReference mDatabase;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final TextView txt = (TextView)findViewById(R.id.txt);
    final FirebaseDatabase database = FirebaseDatabase.getInstance();

    //mDatabase.addValueEventListener(postListener);


    final RatingBar rBar = (RatingBar) findViewById(R.id.rBar);
    rBar.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {

        @Override
        public void onRatingChanged(RatingBar ratingBar, float rating,
                                    boolean fromUser) {
            r1 = rBar.getNumStars();
            //r1=rating;
            mDatabase = database.getReference();
            mDatabase.child(LEC_ID).addChildEventListener(childEventListener);
            rat = (rating+r)/n;
            rBar.setRating(rat);
            Toast.makeText(MainActivity.this, "рейтинг: " + String.valueOf(rating)+" "+r,
                    Toast.LENGTH_LONG).show();
            mDatabase.child(LEC_ID).child("n").setValue(n);
            mDatabase.child(LEC_ID).child("r").setValue(r2);
        }
    });
}

ChildEventListener childEventListener = new ChildEventListener() {

    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {

    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String s) {
        GenericTypeIndicator<Map<String, Float>> genericTypeIndicator = new GenericTypeIndicator<Map<String, Float>>() {}; //here it crashes
        Map<String, Float> map = dataSnapshot.getValue(genericTypeIndicator );
        n = map.get("n")+1;
        r = map.get("r");
    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String s) {

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        // Getting Post failed, log a message
        Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
        // ...
    }
};
 }