Android custom listview with checkbox detect if no checkbox is checked

I have a menu item wherein if it is clicked I need to check first if a checkbox is checked. If not then display a toast message.

This is what I've tried so far:

 SparseBooleanArray checkedPositions = lv.getCheckedItemPositions();
            int size = checkedPositions.size();
            for (int i = 0 ; i < size ; i++) {
                // We get the key stored at the index 'i'
                int key = checkedPositions.keyAt(i);
                // We get the boolean value with the key
                Log.i ("SavedItems", "checkedPositions(" + key + ") = " + checkedPositions.get(key));
            }

            if(size < 1) {
                Toast.makeText(getActivity(), "No item selected", Toast.LENGTH_SHORT).show();
            } 

This is working if no checkbox is checked but if I check and uncheck it's not firing the toast message. Any ideas? Thanks.