how do I correctly implement Filterable to search in a BaseAdapter?

Question

I display a friend list in a ListView and use a TextWatcher set on an EditText to allow search. This works with 1 limitation (which I am not getting): typing a character correctly filters the list, removing a char however doesn't do anything. The original list is correctly displayed when the input is empty, but the Filter is also supposed to work when a character gets removed, since onTextChanged() gets invoked. Where am I going wrong?

Class (BaseAdapter) fields:

private ArrayList<User> friends;
private ArrayList<User> originalFriendList;
//to keep track of the original list
this.originalFriendList = friends;

Filter class:

      private class FriendSearchFilter extends Filter {

    @Override
    protected FilterResults performFiltering(CharSequence constraint) {
        FilterResults results = new FilterResults();
        if (constraint != null && constraint.length() > 0) {

            ArrayList<User> filterList = new ArrayList<User>();

            for (User friend : friends) {
                if (StringUtils.containsIgnoreCase(friend.getLast_name(), constraint)
                        || StringUtils.containsIgnoreCase(friend.getFirst_name(), constraint)) {
                    filterList.add(friend);
                }
            }
            results.count = filterList.size();
            results.values = filterList;
        } else {
             // the input is empty
            results.count = originalFriendList.size();
            results.values = originalFriendList;
        }
        return results;
    }

    @Override
    @SuppressWarnings("unchecked")
    protected void publishResults(CharSequence constraint, FilterResults results) {
        friends = (ArrayList<User>) results.values;
        notifyDataSetChanged();
    }
}

TextWatcher:

                 etSearch.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence charSequence, int start,
                                      int before, int count) {
            /* no action required */
        }

        @Override
        public void onTextChanged(CharSequence charSequence, int start, int count, int after) {
            if(mFriendListFrag == null || !mFriendListFrag.equals(mFragAdapter.getItem(mViewPager.getCurrentItem())));
                mFriendListFrag = (FriendListFragment) mFragAdapter.getItem(mViewPager.getCurrentItem());
                mFLAdapter = (FriendListAdapter) mFriendListFrag.getListAdapter();
            mFLAdapter.getFilter().filter(charSequence.toString());
            Log.e("ON", "TEXT CHANGED");
        }

        @Override
        public void afterTextChanged(Editable editable) {
             /* no action required */
        }
    });

Answer 1

just in case someone has a similar problem: I had to compare the constraint against the original list, and not the "working list" that was overwritten at the time I tried to filter backwards:

        for (User friend : originalFriendList)

instead of

        for (User friend : friends)