I have the following activity:

public class EventGuestListForHostActivity extends AppCompatActivity {

    private ListView guestsListView;

    private ArrayList<Guest> guestsArrayList;

    private DatabaseReference dbReferenceEvent;

    private GuestListGuestNameAdapter guestListAdapter;

    private String eventId;
    private String guestKey;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.d("HMMM", "test");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_event_guest_list_for_host);

        guestsListView = (ListView) findViewById(R.id.guestListView);

        guestsArrayList = new ArrayList<>();

        dbReferenceEvent = FirebaseDatabase.getInstance()
                .getReference("Event");

        guestListAdapter = new GuestListGuestNameAdapter(this, R.layout.guest_list_adapter, guestsArrayList);
        guestsListView.setAdapter(guestListAdapter);

        eventId = getIntent().getExtras().getString("event_id");

        guestsListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

                Guest g = (Guest) adapterView.getItemAtPosition(i);

                Intent intent = new Intent(EventGuestListForHostActivity.this, HostApproveAndDeny.class);
                intent.putExtra("guest_id", g.userId);
                intent.putExtra("member_id", g.memberId);
                intent.putExtra("event_id", eventId);
                intent.putExtra("guest_key", g.guestKey);
                intent.putExtra("approval_status", g.approvalStatus);
                intent.putExtra("guest_name", g.name);

                startActivity(intent);
            }
        });

        guestsArrayList.clear();
        guestListAdapter.clear();
        guestListAdapter.notifyDataSetChanged();
        getData();
    }

    public void getData() {
        guestsArrayList.clear();
        guestListAdapter.clear();
        guestListAdapter.notifyDataSetChanged();
        dbReferenceEvent.child(eventId).child("guestList").addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                Guest guest = snapshot.getValue(Guest.class);
                guest.guestKey = snapshot.getKey();
                guestsArrayList.add(guest);
                guestListAdapter.notifyDataSetChanged();
            }

            @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) {

            }
        });
    }

    @Override
    public void onResume() {
        super.onResume();
        guestsArrayList.clear();
        guestListAdapter.clear();
        guestListAdapter.notifyDataSetChanged();

        guestsListView.setAdapter(null);
        guestListAdapter = null;

        guestListAdapter = new GuestListGuestNameAdapter(this, R.layout.guest_list_adapter, guestsArrayList);
        guestsListView.setAdapter(guestListAdapter);
        
        getData();

    }

When a user returns to this activity by pressing the android back button, I want the ListView to be repopulated (since some data from Firebase may have changed). With the current code I have the ListView always has duplicates for each element, event when the activity is started for the first time. I am not sure why the numerous clears I am using don't prevent that from happening. Any help or pointers are appreciated.

CodePudding user response：

You don't need to call getData in onCreate because onResume will be called anyway even if you are first time entering the Activity/Fragment. So you can remove call from onCreate. That is why you have duplicates even the first time.