EventChannel

Stream native events with EventChannel.

What is EventChannel?

EventChannel is a channel that provides a continuous event stream from the native side to Dart. It is used for continuously updating data such as sensor data or battery level changes. The receiveBroadcastStream method returns a Stream and is listened to with listen.

const eventChannel = EventChannel('samples.flutter.dev/sensor');
eventChannel.receiveBroadcastStream().listen((event) {
  print(event);
});

receiveBroadcastStream

The receiveBroadcastStream method turns an EventChannel into a stream. This stream emits every event from the native side. The listener is registered with listen, and the callback is called when an event arrives. The stream can be canceled with cancel.

final stream = eventChannel.receiveBroadcastStream();
final sub = stream.listen((event) {
  print(event);
});

Exercise Listen to an EventChannel

Create an EventChannel, get the stream with receiveBroadcastStream and listen with listen, printing the incoming event. Wait 10 milliseconds.

Show example solution

class EventChannel {
  final String name;
  EventChannel(this.name);
  Stream<dynamic> receiveBroadcastStream() => Stream.value(42);
}

void main() async {
  const eventChannel = EventChannel('samples.flutter.dev/sensor');
  eventChannel.receiveBroadcastStream().listen((event) {
    print(event);
  });
  await Future.delayed(Duration(milliseconds: 10));
}

Test yourself

When is EventChannel preferred?
- Only for error handling
- To save to the database
- For a one-time method call
- For a continuous event stream
Show answer

For a continuous event stream — EventChannel is preferred for continuous event streams; for one-time calls you use MethodChannel.

Get the stream and listen

eventChannel.____().listen((event) {
  print(event);
});

Show answer

eventChannel.receiveBroadcastStream().listen((event) {
  print(event);
});

EventChannel parts

EventChannel

Event stream channel
receiveBroadcastStream

Produces a stream
listen

Listens to events
stream

Continuous data flow

Next lesson: Summary - Platform channel

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