CODEWITHSUNDEEP
javafirebasefirebase-realtime-databaselistener
Maximilian von Unwerth
Maximilian von Unwerth

Reputation: 577

What can I do instead of waiting for FirebaseDatabase data?

i've a problem with the FirebaseDatabase. I want to read the count of childs from a datebase reference. And I want to do this 5 times. So I created 5 SingleEventListeners and set the value, if there's no user for this date. (I hope you understand, what I want to do :D)

while (counter<5) { 

            ... We create a new date and username here. We have to do this 5 times

            myRef.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                if (!(dataSnapshot.child(finalDate).hasChild(username)))
                      myRef.child(finalDate).child(username).setValue(true);
                }
                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
            counter++;
        }
            try { //TODO Synchronisation is not given without that block
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

   ...
   ...
   ...



myRef.child(chosenDate).child(username).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            participate.setChecked((Boolean) dataSnapshot.getValue());
        }

Here we get a Nullpointer Exception, if we don't wait for receiving the date. What can I do instead of the use of sleep(), which is really bad :(

Upvotes: 0

Views: 94

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598728

Thread.sleep() is hardly ever the solution you want. In this case, since you know how many items you're loading, you can just count the number of items that have loaded (or definitely failed to load):

myRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
    if (!(dataSnapshot.child(finalDate).hasChild(username)))
        myRef.child(finalDate).child(username).setValue(true);
        counter++;
        if (counter == 5) {
            // TODO: whatever you want to do after all items have loaded
        }
    }
    @Override
    public void onCancelled(DatabaseError databaseError) {
        counter++;
        if (counter == 5) {
            // TODO: whatever you want to do after all items have loaded
        }
    }
});

Upvotes: 1

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