What is the difference between Sink and Stream in Flutter?

Question

The Google I/O 2018 video about Flutter explains how to use Dart streams to manage state in a Flutter application. The speaker talked about using Sink as input stre

Answer 1

Let us take a simple example of SINKS & STREAMS in Flutter. Please Reade the comments

       class LoginBloc {
          final _repository = Repository();
          final _loginResponse = BehaviorSubject();  //---->> a simple Sink
          Stream get isSuccessful => _loginResponse.stream; //-----> Stream linked with above sink

        /*
       *  Below is an async function which uses Repository class
       *  to hit a login API and gets the result in a variable
       *  isUserLoginSuccessful[true/false]. and then Add the result 
       *  into the sink.
       *  now whenever something is added to the sink, a callback is given to
       *  the stream linked to that Sink, which is managed by the framework itself 
       *  
       */

         Future getLoginResponse() async { 
            bool isUserLoginSuccessful = await _repository.processUserLogin();
            _loginResponse.sink.add(isUserLoginSuccessful);
          }

          dispose() {
            _loginResponse.close();
          }
        }

Now, I am using this LoginBloc in Login Screen.

     class Login extends StatelessWidget {
      final LoginBloc loginBloc;  // ----> Here is the Object of LoginBloc
      Login(this.loginBloc);

      void _onClickLoginButton() async {
        // Hit login API
        // fetch Login API response data
        loginBloc.getLoginResponse(); //------> here is the function we are using in Login
      }

      @override
      Widget build(BuildContext context) {
        return StreamBuilder(    // ----> You need to use a StreamBuilder Widget on the top Root, or according to the Business logic
          stream: loginBloc.isSuccessful,   // ----> here is the stream which is triggered by Sink which is linked by this stream
          builder: (context, snapshot) {
        // DO WHATEVER YOU WANT AFTER CALLBACK TO STREAM
});

i hope this may make your stream & sink concept more clearer.