Comprehensive Guide To Building Real-Time Apps With Flutter and WebSockets

Summary

While Flutter, a Google-backed software development kit (SDK), facilitates the development of cross-platform dynamic applications, technologies like Flutter WebSockets enable the development of real-time functionalities. 

In this blog post, we will explore how you can build real-time applications using Flutter WebSockets neatly. You can do it yourself if you have the technical proficiency and resources. Or Hire Flutter Developers and get started! 

What are Real-Time Applications?

Let’s check some examples of real-time applications that we often use! 

• Instant Messaging or Chat Application: WhatsApp, Instagram, Facebook Messenger, etc. where users can instantly connect with friends and community and share messages. 
• Multiplayer Online Games: Online games like PUBG, BGMI, etc. let players from across the world connect and play the game in an immersive virtual world. 
• Collaborative Editing and Document Sharing: Have you ever worked with Google Docs where two or more users can collaborate on an article at the same time? It is also an example of a real-time application where the changes are reflected in the document immediately for the various authorized users. 
• Live Streaming and Broadcasting: YouTube Live, Facebook Live, and other sports streaming apps are some examples of real-time applications. Such applications help broadcast audio and video to audiences in real-time. 

Then, let’s talk about WebSockets first! 

What are WebSockets?

WebSockets replace short-lived HTTP connections and allow for instantaneous data exchange between client and server. They can be used with various technologies, such as JS frameworks, Flutter SDK, etc., to create engaging applications. 

Here, we will help you with the steps to build real-time applications using WebSocket in Flutter. Before that, let’s explore the WebSocket communication lifecycle. 

WebSocket Communication Lifecycle

II. Open Connection: Once the connection is established, the WebSocket channel Flutter remains in an open state until and unless either the client or server closes it. The open state allows for data or message exchange in real time over the Flutter WebSocket connection. 

III. Message/ Information Exchange: Based on the data type you transmit, it could be binary frames, text frames, control frames, etc. The server and Client both can listen to the incoming messages and process them. 

IV. Error Handling: You may encounter errors, server failures, or network issues at any point during the WebSocket connection lifecycle. These errors are handled smartly by the client or server by logging it or closing the connection prematurely. 

V. Connection Termination: Once the message is exchanged, the connection termination request can be sent by either the server or client by sensing a close frame. If the other party sends a close frame in response, the connection ends neatly. 

VI. Cleanup: After the connection is terminated, any/all allocated resources for the connection should be released. It includes cleanup tasks, releasing sockets, closing file handles, etc.

How to Use WebSockets With Flutter?

1.  If you want to develop apps for a single platform (say mobile, web, or desktop), you can do that conveniently using the ‘WebScoket’ Class. This class comes out of the box with the programming language that is used to build Flutter SDK – Dart.
2.  If you want your app to run on multiple platforms, WebSocket class won’t work in that case. However, you can explore the Web_Socket_Channel developed by Dart to build a cross-functional app. The channel encapsulates dart:html with dart:io to develop a multiplatform app. 

Steps to Build Real-Time Apps With Flutter + WebSockets

Before getting into the complications of WebSocket, let’s first set up your Flutter CLI to build a Flutter application. Use the Flutter Command Line Interface to start your project. 

flutter create example1

cd example1

Next, you have to import the necessary packages, including WebSocket into your Dart files. 

import 'package:flutter/material.dart';
import 'package:web_socket_channel/web_socket_channel.dart';

Now that you have added the WebSocket package, you need to incorporate it into your ‘pubspec.yaml’ file to start using it. Doing this helps establish a connection between the client (Flutter application) and the server. 

dependencies:

web_socket_channel: ^2.1.0

Now, run this terminal command to install this package. 

flutter pub get

import 'package:web_socket_channel/web_socket_channel.dart';

Step 4: Building a WebSocket Connection 

To establish a connection, you need to create a WebSocket channel first. Then, you use the WebSocketChannel.connect() constructor to establish a connection with the URL you provide. 

import 'package:web_socket_channel/io.dart';
   final channel = IOWebSocketChannel.connect(
     Uri.parse('ws://yourWebSocketServer/path'),
   );

In WebSocket Flutter, you use the sink.add() function of the WebSocketChannel to send data to the server. It acts as a repository that stores the data you want to transmit and then transmits it to the server. 

channel.sink.add('Hello');

The stream.listen() function is used to listen or receive the sent data over the channel. It could be either a broadcasted message for multiple clients or something specific to you. 

channel.stream.listen((message) {
     print('Received: $message');
   });

After you have successfully sent/received messages and no longer need the WebSocket connection, you have to terminate the connection and release the resources so that your Flutter app works smoothly. 

Void dispose() {
channel.sink.close();
super.dispose();
}

Furthermore, let’s not forget to read the pros and cons of using WebSockets with Flutter. 

Pros and Cons of WebSocket

• The persistent client-server connection enables the client or server to send data at any time. 
• The data is sent without any delay. Thereby reducing any potential wastage of bandwidth or resources. 
• With WebSockets, a server can send or broadcast data to multiple clients at the same time. 
• Both client and server can send/receive data with WebSockets. 

• If you are using an outdated browser, WebSockets may not work with it. 
• You may find some restrictions or difficulties with firewalls, proxy servers, and anti-virus protections as they tend to block WebSocket communication. 
• As HTTP is stateless, it handles abandoned connections seamlessly. However, that could cause a problem in situations when a client disconnects abruptly. Even in such a situation, the server still perceives the connection as active. So, these issues have to be taken care of. 

Conclusion

While working with WebSockets may seem like a challenge at first, it is easier than you think. Check out our detailed guide on how to build real-time applications using Flutter and WebSocket and get started.