compare method
Compares two items according to this sort order.
Implementation
int compare(T a, T b) {
if (_comparator != null) {
return _comparator(a, b);
}
if (_fieldSelector != null) {
final valueA = _fieldSelector(a);
final valueB = _fieldSelector(b);
final result = valueA.compareTo(valueB);
return _direction == SortDirection.descending ? -result : result;
}
return 0;
}