Ably Flutter Plugin

A Flutter plugin wrapping the ably-cocoa (iOS) and ably-java (Android) client library SDKs for Ably, the realtime data delivery platform.

Ably provides the best infrastructure and APIs to power realtime experiences at scale, delivering billions of realtime messages everyday to millions of end users. We handle the complexity of realtime messaging so you can focus on your code.

Resources

• Quickstart Guide
• Introducing the Ably Flutter plugin by Srushtika (Developer Advocate)
• Building a Realtime Cryptocurrency App with Flutter by pr-Mais and escamoteur
• Building realtime apps with Flutter and WebSockets: client-side considerations

Supported Platforms

iOS

iOS 9 or newer.

Android

API Level 19 (Android 4.4, KitKat) or newer.

This project uses Java 8 language features, utilising Desugaring to support lower versions of the Android runtime (i.e. API Levels prior to 24)

If your project needs support for SDK Version lower than 24, Android Gradle Plugin 4.0.0+ must be used. You might also need to upgrade gradle distribution accordingly.

Known Limitations

Features that we do not currently support, but we do plan to add in the future:

• Symmetric encryption (#104)
• Ably token generation (#105)
• REST and Realtime Stats (#106)
• Push Notifications target (#107)
• Custom transportParams (#108)
• Push Notifications Admin (#109)
• Remember fallback host during failures (#47)

Running the example

• Clone the repo
• cd to example folder
• run flutter packages get to install dependencies
• flutter run will start the application on connected android / iOS device

Usage

Specify Dependency

Package home: pub.dev/packages/ably_flutter

See: Adding a package dependency to an app

Import the package

import 'package:ably_flutter/ably_flutter.dart' as ably;

Configure a Client Options object

final clientOptions = ably.ClientOptions.fromKey("<YOUR APP KEY>");
clientOptions.logLevel = ably.LogLevel.verbose; // optional

Using the REST API

Creating the REST client instance:

ably.Rest rest = ably.Rest(options: clientOptions);

Getting a channel instance

ably.RestChannel channel = rest.channels.get('test');

Publishing messages using REST:

// both name and data
await channel.publish(name: "Hello", data: "Ably");

// just name
await channel.publish(name: "Hello");

// just data
await channel.publish(data: "Ably");

// an empty message
await channel.publish();

Get REST history:

void getHistory([ably.RestHistoryParams params]) async {
    // getting channel history, by passing or omitting the optional params
    var result = await channel.history(params);

    var messages = result.items; //get messages
    var hasNextPage = result.hasNext(); //tells whether there are more results
    if(hasNextPage){    
      result = await result.next();  //fetches next page results
      messages = result.items;
    }
    if(!hasNextPage){
      result = await result.first();  //fetches first page results
      messages = result.items;
    }
}

// history with default params
getHistory();

// sorted and filtered history
getHistory(ably.RestHistoryParams(direction: 'forwards', limit: 10));

Get REST Channel Presence:

void getPresence([ably.RestPresenceParams params]) async {
    // getting channel history, by passing or omitting the optional params
    var result = await channel.presence.get(params);

    var presenceMembers = result.items; //returns PresenceMessages
    var hasNextPage = result.hasNext(); //tells whether there are more results
    if(hasNextPage){
      result = await result.next();  //fetches next page results
      presenceMembers = result.items;
    }
    if(!hasNextPage){
      result = await result.first();  //fetches first page results
      presenceMembers = result.items;
    }
}

// getting presence members with default params
getPresence();

// filtered presence members
getPresence(ably.RestPresenceParams(
  limit: 10,
  clientId: '<clientId>',
  connectionId: '<connectionID>',
));

Using the Realtime API

Creating the Realtime client instance:

ably.Realtime realtime = ably.Realtime(options: clientOptions);

Listening for connection state change events:

realtime.connection
  .on()
  .listen((ably.ConnectionStateChange stateChange) async {
    print('Realtime connection state changed: ${stateChange.event}');
    setState(() {
      _realtimeConnectionState = stateChange.current;
    });
});

Listening for a particular connection state change event (e.g. connected):

realtime.connection
  .on(ably.ConnectionEvent.connected)
  .listen((ably.ConnectionStateChange stateChange) async {
    print('Realtime connection state changed: ${stateChange.event}');
    setState(() {
      _realtimeConnectionState = stateChange.current;
    });
});

Creating a Realtime channel instance:

ably.RealtimeChannel channel = realtime.channels.get('channel-name');

Listening for channel events:

channel.on().listen((ably.ChannelStateChange stateChange){
  print("Channel state changed: ${stateChange.current}");
});

Attaching to the channel:

await channel.attach();

Detaching from the channel:

await channel.detach();

Subscribing to receive messages received on the channel:

var messageStream = channel.subscribe();
var channelMessageSubscription = messageStream.listen((ably.Message message){
  print("New message arrived ${message.data}");
});

Use channel.subscribe(name: "event1") or channel.subscribe(names: ["event1", "event2"]) to listen to specific named messages.

UnSubscribing from receiving messages on the channel:

await channelMessageSubscription.cancel();

Publishing channel messages

// both name and data
await channel.publish(name: "event1", data: "hello world");
await channel.publish(name: "event1", data: {"hello": "world", "hey": "ably"});
await channel.publish(name: "event1", data: [{"hello": {"world": true}, "ably": {"serious": "realtime"}]);

// single message
await channel.publish(message: ably.Message()..name = "event1"..data = {"hello": "world"});

// multiple messages
await channel.publish(messages: [
  ably.Message()..name="event1"..data = {"hello": "ably"},
  ably.Message()..name="event1"..data = {"hello": "world"}
]);

Get realtime history

void getHistory([ably.RealtimeHistoryParams params]) async {
    var result = await channel.history(params);

    var messages = result.items; //get messages
    var hasNextPage = result.hasNext(); //tells whether there are more results
    if(hasNextPage){    
      result = await result.next();  //fetches next page results
      messages = result.items;
    }
    if(!hasNextPage){
      result = await result.first();  //fetches first page results
      messages = result.items;
    }
}

// history with default params
getHistory();

// sorted and filtered history
getHistory(ably.RealtimeHistoryParams(direction: 'forwards', limit: 10));

Caveats

RTE6a compliance

Using the Streams based approach doesn't fully conform with RTE6a from our client library features specification.

The Problem

StreamSubscription subscriptionToBeCancelled;

// Listener registered 1st
realtime.connection.on().listen((ably.ConnectionStateChange stateChange) async {
  if (stateChange.event == ably.ConnectionEvent.connected) {
    await subscriptionToBeCancelled.cancel();       // Cancelling 2nd listener
  }
});

// Listener registered 2nd
subscriptionToBeCancelled = realtime.connection.on().listen((ably.ConnectionStateChange stateChange) async {
  print('State changed');
});

In the example above, the 2nd listener is cancelled when the 1st listener is notified about the "connected" event. As per RTE6a, the 2nd listener should also be triggered. It will not be as the 2nd listener was registered after the 1st listener and stream subscription is cancelled immediately after 1st listener is triggered.

This wouldn't have happened if the 2nd listener had been registered before the 1st was.

However, using a neat little workaround will fix this...

The Workaround - Cancelling using delay

Instead of await subscriptionToBeCancelled.cancel();, use

Future.delayed(Duration.zero, (){
    subscriptionToBeCancelled.cancel();
});

Contributing

For guidance on how to contribute to this project, see CONTRIBUTING.md.