Android ListView更新项，Firebase数据库

I have a code:

我有一个代码:

@Override
protected void onCreate(Bundle savedInstanceState) {
    .........

    listViewMyAccountSettings = (ListView) findViewById(R.id.listViewMyAccountSettings);
    arrayList = new ArrayList();
    arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, arrayList);
    listViewMyAccountSettings.setAdapter(arrayAdapter);
    arrayAdapter.notifyDataSetChanged();



    listViewMyAccountSettings.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            if (position == 0){
                showAlertUsername();
            } else if (position == 1){
                showAlertAge();

            }
          ......................
        }
    });
         .................
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference myRef = database.getReference("userdata").child(myEmail).child("username");
    myRef.addValueEventListener(new ValueEventListener() {
        @SuppressLint("SetTextI18n")
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // This method is called once with the initial value and again
            // whenever data at this location is updated.
            username = dataSnapshot.getValue(String.class);
            arrayList.add("Your username: " + username);
        }

        @Override
        public void onCancelled(DatabaseError error) {
            // Failed to read value
            Log.w("TAG", "Failed to read value.", error.toException());
        }
    });
@Override
protected