why is adapter.clear() clearing both adapter and arrayList

Question

In this activity, i am fetching all contacts and showing in listView and there is a EditText to search the contact like, if i write "ni" then the listView will show all contact starting with "ni". to do so i am using adapter.clear() and adapter.addAll(matchedContacts, all contact start with "ni") for every key stroke. But here the problem is that every call of adapter.clear() is clearing the main list of contact that is contactList (where i have stored all contacts) and filling it with matchedContacts, beacause of that if i change EditText the listView is not populating with new contact.

Here is the code:

public class AddPerson2 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_addperson2);

        EditText searchContact = (EditText)findViewById(R.id.contact_search);
        final ListView listView =  (ListView)findViewById(R.id.contact_list);
        final ArrayList<String[]> contactList = new ArrayList<>();

        ContentResolver contentResolver = getContentResolver();
        Cursor cursor = contentResolver.query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
                new String[]{ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME
                        , ContactsContract.CommonDataKinds.Phone.NUMBER}
                , null, null, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME + " ASC");
        if (cursor != null){
            if (cursor.getCount() > 0){
                while (cursor.moveToNext()){
                    String[] contact = new String[2];
                    contact[0] = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    contact[1] = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                    contactList.add(contact);
                }
            }
        }

        final ContactListAdapter contactListAdapter = new ContactListAdapter(this, contactList);
        listView.setAdapter(contactListAdapter);

        searchContact.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                String startingCharacter = s.toString().toLowerCase();

                ArrayList<String[]> matchedContacts = new ArrayList<>();

                for (String[] contact : contactList) {
                    if (contact[0].toLowerCase().startsWith(startingCharacter)){
                        matchedContacts.add(contact);
                    }
                }

                contactListAdapter.clear();
                contactListAdapter.addAll(matchedContacts);
            }
        });

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                view.setBackgroundColor(getResources().getColor(R.color.personSelectBackground));
                Log.wtf("showid", id+"");
            }
        });
    }
}

Answer 1

If ContactListAdapter is an ArrayAdapter, then clear() is behaving as expected:

• It calls clear() on the underlying ArrayList, thereby emptying it
• It calls notifyDataSetChanged() on the attached AdapterView, to let it know about the changes in the data

Perhaps you want to be using filtering on the adapter, by calling getFilter().filter() on the adapter. This sample app demonstrates this, though I use a SearchView instead of an EditText.