update method
Implementation
void update(Position position) {
final start = _start;
if (start == null) {
return;
}
if (position.isBefore(start) && !_endFixed) {
_endFixed = true;
_end = _start;
}
if (position.isAfter(start) && _endFixed) {
_endFixed = false;
_start = _end;
}
if (_endFixed) {
_start = position;
} else {
_end = position;
}
// print('($_start, $end');
}