Why arraylist can't add string?

Question

In my code i made

ArrayList<String> allpromo =new ArrayList<>();

as global variable and in onCreate(){}

i wrote

database.getReference().child("PromoCodes").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                allpromo.clear();
                for(DataSnapshot snapshot1 : snapshot.getChildren())
                {
                    String val=snapshot1.child("Promo").getValue(String.class);
                    Toast.makeText(getApplicationContext(), val, Toast.LENGTH_SHORT).show();
                    allpromo.add(val);
                }

            }

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

            }
        });


if(allpromo.isEmpty()) {
          Toast.makeText(getApplicationContext(), "0", Toast.LENGTH_SHORT).show();
      }

It is displaying me all contents of "Promo" from firebase but why it is not able to add items in arraylist. Beacause it Toast "0" .It means mine arraylist is remain empty.And still it Toast items of firebase

But why?enter image description here

and my database is

Loading data from Firebase requires it to make a call over the internet. Like many cloud-based APIs/SDKs, Firebase implements this as an asynchronous operation so that your user can continue to use the app while the data is being retrieved. Then when the data is available, your `onDataChange` is called with that data. But by that time, your toast has long since shown the empty `allpromo`. The solution for this is always the same: all code that needs the data from the database, has to be inside `onDataChange`, be called from there, or otherwise synchronized. — Frank van Puffelen, Feb 26 '22 at 15:29

Adnan Bashir · Accepted Answer · 2022-02-26T15:30:54.447

0

database.getReference().child("PromoCodes").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                allpromo.clear();
                for(DataSnapshot snapshot1 : snapshot.getChildren())
                {
                    String val=snapshot1.child("Promo").getValue(String.class);
                    Toast.makeText(getApplicationContext(), val, Toast.LENGTH_SHORT).show();
                    allpromo.add(val);
                }
         if(allpromo.isEmpty()) {
          Toast.makeText(getApplicationContext(), "0", 
                 Toast.LENGTH_SHORT).show();
      }

            }

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

            }
        });

edited Feb 26 '22 at 15:30

answered Feb 26 '22 at 11:39

Adnan Bashir

645
4
8

still not adding – beginner developer Feb 26 '22 at 12:27
show me the value of snapshot1.child("Promo") in firebase – Adnan Bashir Feb 26 '22 at 12:52
adnan i marked that if add individually any value let suppose "1" like allpromo.add("1"); in that for loop than still it shows that arraylist is empty,But if i add any value outstide addValueEventListner{..} then it work perfectly – beginner developer Feb 26 '22 at 12:57
But i dont why it is happening – beginner developer Feb 26 '22 at 12:58
adnan i edited see please – beginner developer Feb 26 '22 at 13:01
their is two possible reasons for this , 1- you toast it from success listener 2-your child name is invalid OS can't wait for awaiting tasks that's why it execute your toast line before the executing success listener because successlistener is Awaiting method – Adnan Bashir Feb 26 '22 at 15:25
i edit please replace this – Adnan Bashir Feb 26 '22 at 15:31
Tx adnan got it – beginner developer Feb 26 '22 at 15:46

Why arraylist can't add string?

1 Answers1