[pigeon] Support typesafe EventChannels

Use case

It would be useful to have typesafe event channels in pigeon as these currently have to be created manually (and type safety has to be ensured manually).

Proposal

Automatically translate Stream getters to event channels:

@HostApi()
abstract class VideoPlayerApi {
  // The following getter represents the new feature:
  Stream<VideoEvent> get videoEvents;
  void dispose();
  void setLooping(LoopingMessage msg);
  void setVolume(VolumeMessage msg);
  void play();
  PositionMessage position();
  void seekTo(PositionMessage msg);
  void pause();
  void setMixWithOthers(MixWithOthersMessage msg);
}

The above example is based on #66710 where an instance of this API represents a single instance of a video player, and so the videoEvents stream would map to an event channel for a particular video player instance.

@gaaclarke

@gaaclarke

No update. Just waiting for better signal that it is worth the investment to make the case to management.

I'd love it too. A good first step would be to generate code for classes that don't appear in the @HostAPI class so that the user can manually serialize them to dicts and send them over the EventChannel.

Please read https://github.com/flutter/flutter/wiki/Issue-hygiene#escalating-an-issue-that-has-the-wrong-priority and https://github.com/flutter/flutter/wiki/Issue-hygiene#thumbs-up-reactions for how to express interest in this feature.

I discovered that this feature has been supported since version 22.7.0 🎉.
I have tried it and confirmed that it works well!

Here's an example of how we can use it:

class ExampleEventData {
  ExampleEventData({
    required this.data,
  });

  final String data;
}

@EventChannelApi()
abstract class ExampleEventChannelApi {
  ExampleEventData exampleStreamEvents();
}

// -----

Stream<ExampleEventData> getExampleEventStream() async* {
  final Stream<ExampleEventData> events = exampleStreamEvents();
  await for (final ExampleEventData event in events) {
    yield event;
  }
}

You can refer to the official example here: https://github.com/flutter/packages/blob/main/packages/pigeon/example/README.md#event-channel-example

I guess I should have mentioned it here when I added it. Kotlin and Swift support Event Channels now. I haven't closed this issue since it hasn't been added to all languages yet. I might close it and open a new one since that will notify people that it is partially complete.

I discovered that this feature has been supported since version 22.7.0 🎉. I have tried it and confirmed that it works well!

Thanks for the feedback! Let me know if you run into any issues, or features that you think it could use!

Thanks for this change - it is exactly what i need! - I did find a case though that would be awesome if you could take into consideration.

in case of the following pigeon

sealed class BobEvent {}

class BobStart extends BobEvent {
  BobStart();
}

the following kotlin is generated, which is invalid - data classes must have a member, and so this should be just a class I think

sealed class BobEvent 

/** Generated class from Pigeon that represents data sent in messages. */
data class BobStart (
) : BobEvent()
 {
  companion object {
    fun fromList(pigeonVar_list: List<Any?>): BobStart {
      return BobStart()
    }
  }
  fun toList(): List<Any?> {
    return listOf(
    )
  }
}

#160501 tracks supporting empty classes.

for now i am just doing this, which works - in case this is useful... while the related PR is in the pipes.

sealed class BobEvent {}

class BobStart extends BobEvent {
  bool? unused;
  BobStart();
}

which generates

data class BobStart (
  val unused: Boolean? = null
) : BobEvent()
 { ... }

Closing as completed with flutter/packages#7892.

Support for other languages/platforms can be tracked here: #161633

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

Navigation Menu

Repository navigation

[pigeon] Support typesafe EventChannels #66711

Use case

Proposal

18 remaining items

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[pigeon] Support typesafe EventChannels #66711

Description

Use case

Proposal

Activity

ryanheise commented on Sep 26, 2020

mirzaeiyan commented on Jul 4, 2021

Adherentman commented on Apr 25, 2022

gaaclarke commented on Apr 25, 2022

claudius-kienle commented on May 26, 2022

c15yi commented on May 31, 2022

brianquinlan commented on Jul 20, 2022

grantsavill commented on Sep 16, 2022

stuartmorgan-g commented on Jan 22, 2023

18 remaining items

Abson commented on Dec 24, 2024

tttocklll commented on Dec 26, 2024

tarrinneal commented on Dec 27, 2024

tarrinneal commented on Dec 27, 2024

time4tea commented on Jan 7, 2025

stuartmorgan-g commented on Jan 7, 2025

time4tea commented on Jan 7, 2025

tarrinneal commented on Jan 15, 2025

github-actions commented on Jan 29, 2025

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions