How to get all the values from the list in firebase database using java?

Question

I want to get all the field values in a list. I tried but I got items as null. Please help me with this. I tried to get all the values using addOnChildEventListener(), but got all the elements as null. So I have no solution that how to get all those values and add them to the appropriate lists as typed in the code.

Here is the code :

    private void listViewDataListener() {
    FirebaseDatabase
            .getInstance()
            .getReference(classCreatorPhoneNo + "/" + "class_list" + "/" + classUuid + "/" + "attendance" + "/" + attendanceDate + "/" + subjectUuid + "/" + lectureRank)
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                    studentStatusList.add(snapshot.child("student_status_list").getValue(String.class));
                    studentUuidList.add(snapshot.child("student_uuid_list").getValue(String.class));
                    cardBackgroundColor.add(snapshot.child("background_color_list").getValue(String.class));
                }

                @Override
                public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

                }

                @Override
                public void onChildRemoved(@NonNull DataSnapshot snapshot) {

                }

                @Override
                public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

                }

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

                }
            });
}

Answer 1

The problem is in all three of your getValue calls, so let's look at one:

studentStatusList.add(snapshot.child("student_status_list").getValue(String.class));

If we look at the student_status_list in your screenshot, it is not a single String value, but rather a list of values. So calling getValue(String.class) on the student_status_list snapshot will return null , because the value of that node is not a string.

If you want to show all values under student_status_list , you can loop over the snapshots children to do so:

for (DataSnapshot statusSnapshot: snapshot.child("student_status_list").getChildren()) {
  String status = statusSnapshot.getValue(String.class));
  studentStatusList.add(status);
}

You'll have to do the same for the other nodes: any time you have multiple children of which you don't know the keys, you can loop over the getChildren() to access those child nodes.