StreamController 和 BehaviorSubject 是 Dart 中的流吗？

Question

I have used StreamBuilder, StreamController, BehaviorSubject, Stream etc.. for some time now. But I am still confused about some definitions. Especially for this question, Is StreamController and BehaviorSubject a Stream in Dart?

The reason why I have this question is because I can find the following words/quotes online:

• BehaviorSubject is a special StreamController... (from the API doc )
• Observable is aa wrapper class that extends Stream. (Observable is a Stream)
• BehaviorSubject extends Subject (BehaviorSubject is a Subject)
• Subject extends Observable (Subject is a Observable)

From the above 4 points from online doc, it gives me: BehaviorSubject is an Observable and then is a Stream. So BehaviorSubject is a Stream. And BehaviorSubject is a StreamController too. Thus StreamController is a Stream.

But if StreamController is a Stream, that will contradict with some other articles that Stream is actually a part of StreamController and you get the Stream from StreamController.stream.

If we talk about Sink, there will be even more confusing.

StreamController implements StreamSink. So a Sink is a special StreamController.

So from all of the above words, I kinda get the following result:

BehaviorSubject = StreamController = Observable = Stream = Sink

In the end, everything are the same thing... Am I crazy?

Edited: (I understand now. Hope it's correct)

To clarify my confusion, I think I have to understand "BehaviorSubject is a special StreamController" this sentence.

By googling and checking some sdk code, I think I understand that BehaviorSubject is a special StreamController, but not vice versa . That will solve my confusion. BehaviorSubject extends Subject, and Subject implements StreamController. Thus "BehaviorSubject is a special StreamController" is correct. But I can't say StreamController is a BehaviorSubject. Thus I can't say StreamController is a Stream even if BehaviorSubject is actually a Stream.

I hope what I understand above is correct.

Answer 1

A StreamController is a StreamController .
It does not extend anything. So it is not any of Observable , Stream , BehaviorSubject or Sink .

It does implement Sink as you said and thus allow you to add data on it directly, ie use streamController.add as well as streamController.sink.add . This data is then passed onto the Stream that each controller carries.

BehaviorSubject is not actually part of the standard library and just a fancy addition to streams from rxdart . It allows you to access the latest value at any time directly.

Answer 2

Not crazy at all, A stream is just like a pipe that take in data as a sink and give it back as a stream, while StreamController is just use to control the the stream. i hope this is helpful

Answer 3

Observable class is deprecated in rxdart 0.23.1

Observable can be replaced by Stream

rxdart-changelog