如何在流中生成Firebase侦听器

Question

Using AngularDart and Firebase, the below code doesn't work because yield is inside an anonymous inner class. How might I rewrite this? I'm new to both Angular and Dart and couldn't find any examples for this.

Essentially I'm trying to listen for items inside a stream in my service, but I'm getting the actual item from firebase and need to pass these firebase items back to the stream.

In the service:

Stream<Item> itemStream() async* {
  final ref = database().ref("items");
  await ref.onChildAdded.listen((e) {
    DataSnapshot snapshot = e.snapshot;
    Map parsedMap = snapshot.val();
    String id = snapshot.key;
    String property1 = parsedMap['property1'];
    String property2 = parsedMap['property2'];
    print(property1);
    print(property2);
    yield new Item(id, property1, property2); // invalid; yield does not work here.
  });
  // yield works here but it's no use here.
}

Component:

var stream = itemListService.itemStream();
await for (var item in stream) {
  print(item.id);
}

Update: I got around this by not using a service. However I thought using a service was better practice so that's why I wanted to do it.

Answer 1

You could do two things.

1) Use a StreamController

2) (Better)

Stream<Item> itemStream() { final ref = database().ref("items"); return ref.onChildAdded.map((e) { DataSnapshot snapshot = e.snapshot; Map parsedMap = snapshot.val(); String id = snapshot.key; String property1 = parsedMap['property1']; String property2 = parsedMap['property2']; print(property1); print(property2); return new Item(id, property1, property2); }