Flutter – WebSockets
WebSockets are used to connect with the server just like the http package. It supports two-way communication with a server without polling.
In this article we will explore the below-listed topics related to WebSockets in Flutter:
- Connecting to a WebSocket server
- Listen to messages from the server.
- Send data to the server.
- Close the WebSocket connection.
In this article as an example, we will connect to the test server provided by websocket.org.
Connect to a WebSocket Server:
The web_socket_channel package has tools that are needed to connect to a WebSocket server. The package provides a WebSocketChannel that allows users to both listen to messages from the server and push messages to the server.
In Flutter, use the following line to create a WebSocketChannel that connects to a server:
final channel = IOWebSocketChannel.connect('ws://echo.websocket.org');
Listen to messages from the server:
Now that we have established the connection to the server, we will send a message to it and get the same message as a response:
Dart
StreamBuilder( stream: widget.channel.stream, builder: (context, snapshot) { return Text(snapshot.hasData ? '${snapshot.data}' : '' ); }, ); |
Send Data to the Server:
To send data to the server, add() messages to the sink provided by the WebSocketChannel as shown below:
channel.sink.add('Hello Geeks!');
Close the Connection:
To close the connection to the WebSocket use the below:
channel.sink.close();
Complete Source Code:
Dart
import 'dart:async' ; import 'dart:convert' ; import 'package:flutter/material.dart' ; import 'package:http/http.dart' as http; Future<Album> fetchAlbum() async { final response = if (response.statusCode == 200) { return Album.fromJson(json.decode(response.body)); } else { throw Exception( 'Loading album failed!' ); } } Future<Album> updateAlbum(String title) async { final http.Response response = await http.put( headers: <String, String>{ 'Content-Type' : 'application/json; charset=UTF-8' , }, body: jsonEncode(<String, String>{ 'title' : title, }), ); if (response.statusCode == 200) { return Album.fromJson(json.decode(response.body)); } else { throw Exception( 'Failed to update the album!' ); } } // the album class class Album { final int id; final String title; Album({ this .id, this .title}); factory Album.fromJson(Map<String, dynamic> json) { return Album( id: json[ 'id' ], title: json[ 'title' ], ); } } void main() { runApp(MyApp()); } class MyApp extends StatefulWidget { MyApp({Key key}) : super(key: key); @override _MyAppState createState() { return _MyAppState(); } } class _MyAppState extends State<MyApp> { final TextEditingController _controller = TextEditingController(); Future<Album> _futureAlbum; @override void initState() { super.initState(); _futureAlbum = getAlbum(); } @override Widget build(BuildContext context) { return MaterialApp( title: 'Update Data' , theme: ThemeData( primarySwatch: Colors.blue, ), home: Scaffold( appBar: AppBar( title: Text( 'GeeksForGeeks' ), backgroundColor: Colors.green, ), body: Container( alignment: Alignment.center, padding: const EdgeInsets.all(8.0), child: FutureBuilder<Album>( future: _futureAlbum, builder: (context, snapshot) { if (snapshot.connectionState == ConnectionState.done) { if (snapshot.hasData) { return Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text(snapshot.data.title), TextField( controller: _controller, decoration: InputDecoration(hintText: 'Enter Title' ), ), RaisedButton( child: Text( 'Update Data' ), onPressed: () { setState(() { _futureAlbum = updateAlbum(_controller.text); }); }, ), ], ); } else if (snapshot.hasError) { return Text( "${snapshot.error}" ); } } return CircularProgressIndicator(); }, ), ), ), ); } } |
Output:
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