selectMany method
Selects multiple objects by id.
Implementation
bool selectMany(Iterable<String> ids) {
final next = <String>[];
for (final id in ids) {
if (objectById(id) != null && !next.contains(id)) next.add(id);
}
final changed = !_sameIds(_selectedObjectIds, next);
_selectedObjectIds
..clear()
..addAll(next);
render();
if (changed) _emitSelect();
return next.isNotEmpty;
}