Firebase: update an integer value

Question

So im coding an inventory management app and I'm using a barcode scanner to scan my products. My idea is that every time that a product gets scanned I need to remove one quantity of it on my database. Like this: Scan product-->quantity=quantity-1

And this is my code

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mFirestore = FirebaseFirestore.getInstance();
        scannerView = new ZXingScannerView(this);
        setContentView(scannerView);
       

    private void updateData() {

   //myresult is the item barcode
        final DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference("Items").child(myresult).child("itemquantity");
        mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                long qty =(long) dataSnapshot.getValue();
                mDatabase.setValue(qty - 1);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    @Override
    public void onDestroy() {
        super.onDestroy();
        scannerView.stopCamera();
    }

   
    private void showMessageOKCancel(String message, DialogInterface.OnClickListener okListener) {
        new AlertDialog.Builder(addquantityactivity.this)
                .setMessage(message)
                .setPositiveButton("OK", okListener)
                .setNegativeButton("Cancel", null)
                .create()
                .show();
    }

    @Override
    public void handleResult(Result result) {
         myResult = result.getText();
        Log.d("QRCodeScanner", result.getText());
        Log.d("QRCodeScanner", result.getBarcodeFormat().toString());

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Scan Result");
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                updateData();
                scannerView.resumeCameraPreview(addquantityactivity.this);
                
            }
        });
        builder.setNeutralButton("Visit", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(myResult));
                startActivity(browserIntent);
            }
        });
        builder.setMessage(result.getText());
        AlertDialog alert1 = builder.create();
        alert1.show();

    }
}

i call updateData() in my handleResult function. The error i get is :

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long

@Dharmaraj yes, it gives ```java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer``` — , Jun 29 '20 at 10:26
Can you try this `int qty= Integer.parseInt(dataSnapshot.getValue());`? — Dharmaraj, Jun 29 '20 at 10:37

Alex Mamo · Answer 1 · 2020-06-29T10:39:03.810

0

That's not the right way to decrement the value of a property in Firebase Realtime Database. Because we are creating apps that will be used in a multi-user environment, a more appropriate approach should be the use of transactions as explained in my answer from the following post:

How to save users score in firebase and retrieve it in real-time in Android studio

Or, in a more simpler way:

mDatabase.setValue(ServerValue.increment(-1));

edited Jun 29 '20 at 10:39

answered Jun 29 '20 at 10:37

Alex Mamo

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Does this work if the value in database is stored in string form as `"1"` ? – Dharmaraj Jun 29 '20 at 10:38
No, it should always be stored as a number and **not** a String. – Alex Mamo Jun 29 '20 at 10:39
Alright, never knew this was possible directly from Android :p – Dharmaraj Jun 29 '20 at 10:40
@Dharmaraj Yes, it is possible ;) – Alex Mamo Jun 29 '20 at 10:40
@AlexMamo Can you be more specific by mentioning it in my code? im new here;p – Jun 29 '20 at 10:51
Please edit your question and add your database structure as a JSON file or at least a screenshot. – Alex Mamo Jun 29 '20 at 10:59

score 0 · Answer 2 · answered Jun 29 '20 at 10:57

0

Try this :

long qty = dataSnapshot.getValue(Long.class);

answered Jun 29 '20 at 10:57

Mohamed Hassan

191
2
12

this worked for me, but only if i have my quantity as an integer in firebase.. I need it to be as string because i get errors in my other functionalities..How to change the answer you gave, so to update a string number? like "3" , to be "4".Not 3 to 4 – Jun 29 '20 at 11:23
so convert it to string : `String qty = String.valueOf(dataSnapshot.getValue(Long.class));` – Mohamed Hassan Jun 29 '20 at 11:24
I already did that but i got another ```Failed to convert a value of type java.lang.String to long``` :p – Jun 29 '20 at 11:28

Firebase: update an integer value

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