watchStream<T extends Object, R> function

AsyncSnapshot<R> watchStream<T extends Object, R>(Stream<R> select(T)?, { T? target, R? initialValue, bool preserveState = true, bool allowStreamChange = false, String? instanceName, GetIt? getIt, })

watchStream subscribes to the Stream returned by select and returns an AsyncSnapshot with the latest received data from the Stream Whenever new data is received it triggers a rebuild. When you call watchStream a second time on the same Stream it will return the last received data but not subscribe another time. To be able to use watchStream inside a build function we have to pass initialValue so that it can return something before it has received the first data if select returns a different Stream than on the last call, watchStream will cancel the previous subscription and subscribe to the new stream. preserveState determines then if the new initial value should be the last value of the previous stream or again initialValue If you want to observe a Stream that is not registered in get_it you can pass it as target. if you pass null as select, T or target has to be a Stream<R>. instanceName is the optional name of the instance if you registered it with a name in get_it.

getIt is the optional instance of get_it to use if you don't want to use the default one. 99% of the time you won't need this.

Implementation

AsyncSnapshot<R> watchStream<T extends Object, R>(
  Stream<R> Function(T)? select, {
  T? target,
  R? initialValue,
  bool preserveState = true,
  bool allowStreamChange = false,
  String? instanceName,
  GetIt? getIt,
}) {
  assert(_activeWatchItState != null,
      'watchStream can only be called inside a build function within a WatchingWidget or a widget using the WatchItMixin');

  final getItInstance = getIt ?? di;
  final parentObject = target ?? getItInstance<T>(instanceName: instanceName);

  // Validate target type when no select function is provided
  if (select == null && parentObject is! Stream<R>) {
    throw ArgumentError(
        'When no select function is provided, target must be a Stream<$R>. '
        'Got: ${parentObject.runtimeType}');
  }

  return _activeWatchItState!.watchStream(
      parentOrStream: parentObject,
      initialValue: initialValue,
      instanceName: instanceName,
      preserveState: preserveState,
      selector: select,
      allowStreamChange: allowStreamChange);
}