您需要的是combineLatest运算符

Observable<Foo> foo;
Observable<Bar> bar;

final output = Observable.combineLatest2(foo, bar, (Foo foo, Bar bar) {
  // TODO: somehow merge them
});

你试过Observable.race吗？它非常适合通知：
给定两个或多个源流，仅从其中的第一个流发出所有项，以发出项或通知。

new Observable.race([
  new Observable.timer(1, new Duration(days: 1)),
  new Observable.timer(2, new Duration(days: 2)),
  new Observable.timer(3, new Duration(seconds: 1))
]).listen(print); // prints 3

了解更多https://pub.dev/documentation/rxdart/latest/rx/Observable/Observable.race.html

使用StreamGroup.merge并检查对象类型：

import 'package:async/async.dart';

Stream<MobileAdEvent> adEventStream;
Stream<Color> colorStream;

final merged = StreamGroup.merge([
  _orderStream.stream,
  _orderStream.stream.map((event) => event.hashCode),
]);

final subscription = merged.listen((event) {
  if (event is MobileAdEvent) {
    // handle event from first stream
  }
  if (event is Color) {
    // handle event from second stream
  }
});