Android- Firebase How to assign a child value under each ArrayList value?

Question

I am trying to make an event sorter app. I'm trying to grab the friends arraylist from the database, and add the event_key under each friend value in the database.

final ArrayList<String> friends= new ArrayList<String>();
hello.addListenerForSingleValueEvent(new ValueEventListener() {
             @Override
             public void onDataChange(DataSnapshot dataSnapshot) {

                 for (DataSnapshot dsp : dataSnapshot.getChildren()) {
                     friends.add(String.valueOf(dsp.getKey())); 
                 }

                 mDatabaseUserEvents.child(invited_list).child(event_key).setValue(true);
             }

             @Override
             public void onCancelled(DatabaseError databaseError) {

             }
         });

However, I get an error saying that ArrayList is not compatible.

The database structure I am trying to aim for is this:

Events:
       -User1:
              -event_key:true
       -User2:
              -event_key:true

I am pretty sure I need to use a for loop, but confused on how to achieve it. Thanks!

Alex Mamo · Accepted Answer · 2017-09-20 08:38:19Z

2

Because Firebase is a NoSQL database, it is structured as pairs of key and values. So every child is a Map and not an ArrayList. It's true that you can get a value from the database and store into an ArrayList but not in the way you do, because of the asynchronous behaviour of onDataChange() method, your friends ArrayList will always be empty. This is happening because onDataChange() method is called even before you are trying to add those values to that ArrayList.

If you want to set true for all the event_key coresponding to each user and assuming that Events node is a direct child of Firebase-database, please use the following code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference eventsRef = rootRef.child("Events");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String userKey = ds.getKey();
            Log.d("TAG", userKey);
            eventsRef.child(userKey).child("event_key").setValue(true);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
eventsRef.addListenerForSingleValueEvent(eventListener);

answered Sep 20, 2017 at 8:38

Alex Mamo

139k18 gold badges171 silver badges202 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Spotz Over a year ago

Awesome! Thank you!

Collectives™ on Stack Overflow

Android- Firebase How to assign a child value under each ArrayList value?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related