Ytukyg

Ok so I've been looking for related articles regarding this, I've made a few experiments but I can't understand why I can't still get the values of note, date_time and vaccine objects... I'm planning on putting them in a ListView and I already got the key from the list of data using ChildEventListener

 lastlastref = myRef.child(babyid).child("baby_features").child("immunization_records");



    lastlastref.addChildEventListener(new ChildEventListener() {

        @Override

        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            String string = dataSnapshot.getValue(String.class);





        }



        @Override

        public void onChildChanged(DataSnapshot dataSnapshot, String s) {



        }



        @Override

        public void onChildRemoved(DataSnapshot dataSnapshot) {



        }



        @Override

        public void onChildMoved(DataSnapshot dataSnapshot, String s) {



        }



        @Override

        public void onCancelled(DatabaseError databaseError) {



        }

    });

and then I've tried using EventListener to get the values inside of it

 lastlastref = myRef.child(babyid).child("baby_features").child("immunization_records");



    lastlastref.addChildEventListener(new ChildEventListener() {

        @Override

        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            String string = dataSnapshot.getValue(String.class);



            DatabaseReference newRef = lastlastref.child(string);



            newRef.addValueEventListener(new ValueEventListener() {

                @Override

                public void onDataChange(DataSnapshot snapshot) {

                    note = snapshot.child("note").getValue(String.class);

                    vaccine = snapshot.child("vaccine").getValue(String.class);

                    timestamp = snapshot.child("date_time").getValue(String.class);



                }

                @Override

                public void onCancelled(DatabaseError databaseError) {

                }

            });

             arrayList.add(vaccine + "" +  timestamp + "" + note);

             adapter.notifyDataSetChanged();



        }



        @Override

        public void onChildChanged(DataSnapshot dataSnapshot, String s) {



        }



        @Override

        public void onChildRemoved(DataSnapshot dataSnapshot) {



        }



        @Override

        public void onChildMoved(DataSnapshot dataSnapshot, String s) {



        }



        @Override

        public void onCancelled(DatabaseError databaseError) {



        }

    });

But the app still crashes and logcat says "Can't pass null for argument 'pathString' in child()"

You set up your reference to:

lastlastref = myRef.child(babyid).child("baby_features").child("immunization_records");

So each child node under this location is a JSON object like this:

{

  "date_time": "November/16/2018...",

  "note": "hhjj...",

  "vaccine": "Measles"

}

But in your onChildAdded, you're trying to retrieve a single string value. Since the above JSON object is not a single string value, the getValue(String.class) returns null.

To get the values, you can call getValue() on the individual properties:

lastlastref.addChildEventListener(new ChildEventListener() {

    @Override

    public void onChildAdded(DataSnapshot dataSnapshot, String s) {

        String date_time = dataSnapshot.child("date_time").getValue(String.class);

        String note = dataSnapshot.child("note").getValue(String.class);

        String vaccine = dataSnapshot.child("vaccine").getValue(String.class);

    }

You can also create a minimal class to wrap each record, and read that. The simplest version of that is:

public class ImmunizationRecord {

  public String date_time;

  public String note;

  public String vaccine;

}

And the reading would then be done with:

public void onChildAdded(DataSnapshot dataSnapshot, String s) {

    String record = dataSnapshot.getValue(ImmunizationRecord.class);

}

A small side note about the way you store date_time. This format will lead to problems as you progress, since it is not sortable. If you need to store time stamps, store them as milliseconds since the epoch, or in a string format that allows them to be sorted (e.g. 2018-11-16T11:29:00).