onParam<T> method
Subscribe to a series of param by key
.
Implementation
@protected
Stream<T> onParam<T>(Comparable key) {
final sc = StreamController<T>();
sc
..onListen = () {
paramStreamCtrls[key] ??= <StreamController<dynamic>>{};
paramStreamCtrls[key]?.add(sc);
// sink lastest value.
final value = getParam<T>(key);
if (value != null) {
sc.add(value);
}
}
..onCancel = () {
paramStreamCtrls[key]?.remove(sc);
};
return sc.stream;
}