What is the difference between Sink and Stream in Flutter?

Sink and Stream both are parts of the StreamController. You add a data to the StreamController using Sink which can be listened via the Stream.

Example:

final _user = StreamController<User>();Sink get updateUser => _user.sink;Stream<User> get user => _user.stream;

Usage:

updateUser.add(yourUserObject); // This will add data to the stream.

Whenever a data is added to the stream via sink, it will be emitted which can be listened using the listen method.

user.listen((user) => print(user)); 

You can perform a various number of actions before the stream is emitted. transform method is an example which can be used to transform the input data before it gets emitted.

A StreamSink is a StreamConsumer, which means it can take several streams (added by addStream) and processes the events these streams emit.

If it is the StreamSink of a StreamController then all events from the added streams are emitted by the stream created by the StreamController.

This way you can pipe (forward) one or more streams into another one.

If you are looking for a very basic definitions on stream and sinks, then refer to this:

Stream - the conveyor belt is called as a stream

StreamController - this is what controls the stream

StreamTransformer - this is what processes the input data

StreamBuilder - it’s a method that takes stream as an input and provides us with a builder which rebuilds every time there is a new value of a stream

sink - the property which takes an input

stream - the property which gives the output out of the Stream

For more details, please refer to this article