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.
1. 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');2. 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}' : '');
},
);
3. 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!');4. Close the Connection
To close the connection to the WebSocket, use the below:
channel.sink.close();Complete Source Code (main.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 = await http
.get(Uri.parse('https://jsonplaceholder.typicode.com/albums/1'));
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(
Uri.parse('https://jsonplaceholder.typicode.com/albums/1'),
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({required this.id, required 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({super.key});
@override
_MyAppState createState() {
return _MyAppState();
}
}
class _MyAppState extends State<MyApp> {
final TextEditingController _controller = TextEditingController();
late Future<Album> _futureAlbum;
@override
void initState() {
super.initState();
_futureAlbum = fetchAlbum();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Update Data',
theme: ThemeData(
primarySwatch: Colors.blue,
),
debugShowCheckedModeBanner: false,
home: Scaffold(
appBar: AppBar(
title: Text('GeeksForGeeks'),
backgroundColor: Colors.green,
foregroundColor: Colors.white,
),
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'),
),
TextButton(
child: Text('Update Data'),
onPressed: () {
setState(() {
_futureAlbum = updateAlbum(_controller.text);
});
},
),
],
);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
}
}
return CircularProgressIndicator();
},
),
),
),
);
}
}
To know more about HTTP pacage, TextButton, FutureBuilder in flutter refer this article: Implementing Rest API in Flutter, Flutter – TextButton Widget, Flutter – FutureBuilder Widget.
Output:
