Should I Actually Remove the Valueeventlistener

Should I actually remove the ValueEventListener?

When talking about listeners, yes, you need to remove them accordingly to the life-cycle of your activity and for this you need to use the following line of code:

databaseReference.removeEventListener(valueEventListener);

Remember if you don't do this, you'll end up wasting your battery and bandwidth. So:

1. If you have added the listener in onStart you have to remove it in onStop.
2. If you have added the listener in onResume you have to remove it in onPause.
3. If you have added the listener in onCreate you have to remove it in onDestroy.

But remember onDestroy is not always called, so the last option in not always a good choice.

There is another approach in which there is no need to remove the listener and that is when using addListenerForSingleValueEvent:

Add a listener for a single change in the data at this location.

Is it necessary to remove each added listener from Firebase Realtime Database?

When you are using "addValueEventListener()", it means that you are attaching a persistent listener to a specific location in the database to get data in real-time. It doesn't really matter if you are adding the listener in a Coroutine context or not, you always need to remove the listener accordingly to the lifecycle of your activity.

If you don't need real-time updates, you can use addListenerForSingleValueEvent(), as it:

Adds a listener for a single change in the data at this location.

So there is no need to remove any listener at all.

You can also use the relatively new added get() method, as explained in one of my articles:

• How to read data from Firebase Realtime Database using get()?

What happens if you don't remove the listener?

Then it will always keep on listening. In an Android context, the listener knows nothing about the Android activity lifecycle. So as said above, so you'll have to explicitly remove it at the right time, so it cannot lead to unexpected results and crashes.

How to remove Firebase EventListener?

Firebase Realtime Database listeners are not automatically removed. They only stop when you explicitly remove them, or when the app gets killed. There is no API to get a list of the active listeners, so you will have to track those yourself.

The earliest you should usually connect your listeners is in onStart, in which case you should remove them in the onStop of the activity.

Firebase listeners still listening after activity being finished

Before going to next Activity remove the value event listener

refState.removeEventListener(listenerName)

Try this code

Inside onCreate

DatabaseReference refState = FirebaseDatabase.getInstance().
    getReference("/Rooms/"+roomName+"/gameState");
refState.addValueEventListener(stateValueEventListner);

Outside onCreate

private ValueEventListener stateValueEventListner = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
           try {
                String gameState = dataSnapshot.getValue(String.class);
                if (gameState.equals("choose_letter")) {
                    System.out.println("Starting game");
                    startGame();
                }
              }
              catch(Exception e)
              {}
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                System.out.println("Error");
            }

        }); 

Remove value event listener

refState.removeEventListener(stateValueEventListner):

Android Firebase keep addListenerForSingleValueEvent updated

If you have enabled offline capabilities, it means that you'll be able to use your app even if it temporarily loses its network connection. So the ValueEventListener will keep listening on the local stored datas as long as you are offline. If you want the results to be updated, then you need to go online.

If you want to listen to data only once, then you need to use: addListenerForSingleValueEvent(). If you want to use addValueEventListener, just don't forget to remove the listener according to the life-cycle of your activity as I have already answered here.

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