combining_streams_example.dart

 // using "startWith" to ensure that the combined stream emitts even though 
 // on of two streams did not emmited any value yet
 var combinedStream = Observable.combineLatest2(
        title.startWith(""), 
        subtitle.startWith(""),
        (title, subtitle) => Pair<String, String>(title, subtitle));

    new StreamBuilder<Pair<String, String>>(
      stream: combinedStream,
      builder: (_, snapshot) {
        if (snapshot.data == null) return Container();
        var pair = snapshot.data;

        return FancyTitleBar(title: pair.first, subtitle: pair.second);
      },
    );


// not sure if there is already an implementation of Pair, there you go: 
class Pair<F, S> {
  F first;
  S second;

  Pair(this.first, this.second);
}