How to update data in Firebase?

Question

I am trying to update the quantity of a product in the database.Whenever I Add or Deduct the quantity, the change only reflects on my app but not updated in the Firebase! Any Help Will be greatly appreciated!

Here is a picture of the app:

Picture of database:

Here is my Code:

public class Edit extends AppCompatActivity {
 String myKey = null;
private Button removebutton, plus, minus;
private int counterValue;
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_edit);
     removebutton = (Button) findViewById(R.id.item_detail_delete);
     plus = (Button) findViewById(R.id.item_quantity_add);
     minus = (Button) findViewById(R.id.item_quantity_remove);

     final DatabaseReference database;
     myKey = getIntent().getExtras().getString("value");
    database = FirebaseDatabase.getInstance().getReference().child("All Barcodes");
    database.child(myKey).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            TextView Barcode=(TextView) findViewById(R.id.Barcode);
            TextView Pname=(TextView) findViewById(R.id.Pname);
            TextView EntryDate=(TextView) findViewById(R.id.EntryDate);
            TextView ExpiryDate=(TextView) findViewById(R.id.ExpiryDate);
            final TextView Quantity=(TextView) findViewById(R.id.Quantity);
                String barcode = (String) dataSnapshot.child("barcode").getValue();
                String pname = (String) dataSnapshot.child("pname").getValue();
                String date = (String) dataSnapshot.child("date").getValue();
                String expiration = (String) dataSnapshot.child("expiration").getValue();
                String quantity = (String) dataSnapshot.child("quantity").getValue();
                Barcode.setText(barcode);
                Pname.setText(pname);
                EntryDate.setText(date);
                ExpiryDate.setText(expiration);
                Quantity.setText(quantity);
            counterValue = Integer.valueOf(quantity);
            plus.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    counterValue ++;
                    Quantity.setText(String.valueOf(counterValue));
                }
            });
            minus.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    counterValue --;
                    Quantity.setText(String.valueOf(counterValue));
                }
            });

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            System.out.println("The read failed: " + databaseError.getMessage());

        }
    });

     removebutton.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
             database.child(myKey).removeValue();
             Intent intent = new Intent(Edit.this,Inventory.class);
             startActivity(intent);
         }
     });

}

Answer 1

You should update the related field in the database yourself:

plus.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        counterValue++;
        Quantity.setText(String.valueOf(counterValue));
        database.child(myKey).child("quantity").setValue(String.valueOf(counterValue));
    }
});
minus.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
       counterValue--;
       Quantity.setText(String.valueOf(counterValue));
       database.child(myKey).child("quantity").setValue(String.valueOf(counterValue));
    }
});

Answer 2

The easiest way is to set keep sync to true like that:

DatabaseReference scoresRef = FirebaseDatabase.getInstance().getReference("scores");
scoresRef.keepSynced(true);

This is from the firebase documentation

https://firebase.google.com/docs/database/android/offline-capabilities