IngredientListActivity.java

listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
                adapter.showCheckboxes = !adapter.showCheckboxes;
                adapter.notifyDataSetChanged();
                return true;
            }
        });