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:
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:
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: