Summary - Streams

Combine listen, map and StreamController to write an event logger.

Summary - Streams

In this group we learned the basics of Streams: Stream represents an event sequence; listen subscribes; map/where transforms; asyncExpand expands; StreamController creates manually.

Together these tools form the foundation of event-driven programming in Dart. They are used for user input, sensor data, network packets and other continuously flowing data.

Now let's do an exercise that uses two tools together: produce events with StreamController, transform with map and print.

Exercise Produce with controller, transform with map

import 'dart:async' is already added. void main() async is already written. Create a StreamController<int>(). Send two events with controller.add(10) and controller.add(20). Close with controller.close(). Double events with controller.stream.map((n) => n * 2). Listen with await for and print with print.

Show example solution

import 'dart:async';

void main() async {
  var controller = StreamController<int>();
  controller.add(10);
  controller.add(20);
  controller.close();
  var doubled = controller.stream.map((n) => n * 2);
  await for (var n in doubled) {
    print(n);
  }
}

Test yourself

Match the stream concepts

Stream

Event sequence
listen

Subscribe
map/where

Transform
StreamController

Manual creation
Which class lets you create your own Stream manually?
- StreamController
- Completer
- Future
- Iterable
Show answer

StreamController — StreamController lets you create your own Stream manually.

Next lesson: typedef

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