Flutter - StreamBuilder Widget
Last Updated :
16 Oct, 2023
A StreamBuilder in Flutter is used to listen to a stream of data and rebuild its widget subtree whenever new data is emitted by the stream. It's commonly used for real-time updates, such as when working with streams of data from network requests, databases, or other asynchronous sources. In this article, we are going to see an example of a Streambuilder Widget by taking an Example.
Syntax of StreamBuilder
StreamBuilder<T>(
stream: yourStream, // The stream to listen to
initialData: initialData, // Optional initial data while waiting for the first event
builder: (BuildContext context, AsyncSnapshot<T> snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return YourLoadingWidget(); // Display a loading indicator while waiting for data
} else if (snapshot.hasError) {
return YourErrorWidget(error: snapshot.error); // Handle errors
} else if (!snapshot.hasData) {
return YourNoDataWidget(); // Handle the case when there's no data
} else {
return YourDataWidget(data: snapshot.data); // Display your UI with the data
}
},
)
Here we are going to see a simple example of a StreamBuilder in Flutter that listens to a stream of numbers and displays the latest number in real-time:
Required Tools
- To build this app, you need the following items installed on your machine:
- Visual Studio Code / Android Studio
- Android Emulator / iOS Simulator / Physical Device device.
- Flutter Installed
- Flutter plugin for VS Code / Android Studio.
A sample video is given below to get an idea about what we are going to do in this article.
Step By Step Implementations
Step 1: Create a New Project in Android Studio
To set up Flutter Development on Android Studio please refer to Android Studio Setup for Flutter Development, and then create a new project in Android Studio please refer to Creating a Simple Application in Flutter.
Step 2: Import the Package
First of all import material.dart file.
import 'dart:async';
import 'package:flutter/material.dart';
Step 3: Execute the main Method
Here the execution of our app starts.
Dart
void main() {
runApp(MyApp());
}
Step 4: Create MyApp Class
In this class we are going to implement the MaterialApp , here we are also set the Theme of our App.
Dart
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.green, // Set the app's primary theme color
),
title: 'StreamBuilder Example',
home: NumberStreamPage(),
);
}
}
Step 5: Create NumberStreamPage Class
In this class we are going to Implement the StreamBuilder to display the numbers changes in real time.Here we are going to run a for loop from 0 to 9 and display the updates number by the help of StreamBuilder.Comments are added for better understanding.
StreamBuilder<int>(
stream: _numberStreamController.stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator(); // Display a loading indicator when waiting for data.
} else if (snapshot.hasError) {
return Text('Error: ${snapshot.error}'); // Display an error message if an error occurs.
} else if (!snapshot.hasData) {
return Text('No data available'); // Display a message when no data is available.
} else {
return Text(
'Latest Number: ${snapshot.data}',
style: TextStyle(fontSize: 24),
); // Display the latest number when data is available.
}
},
),
Dart
class _NumberStreamPageState extends State<NumberStreamPage> {
late StreamController<int> _numberStreamController;
@override
void initState() {
super.initState();
// Create a stream controller and add numbers to the stream.
_numberStreamController = StreamController<int>();
_startAddingNumbers(); // Start adding numbers to the stream.
}
void _startAddingNumbers() async {
for (int i = 0; i < 10; i++) {
await Future.delayed(Duration(seconds: 2)); // Delay for 2 seconds.
_numberStreamController.sink.add(i); // Add the number to the stream.
}
}
@override
void dispose() {
_numberStreamController.close(); // Close the stream when disposing.
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('StreamBuilder Example'),
),
body: Center(
child: StreamBuilder<int>(
stream: _numberStreamController.stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator(); // Display a loading indicator when waiting for data.
} else if (snapshot.hasError) {
return Text('Error: ${snapshot.error}'); // Display an error message if an error occurs.
} else if (!snapshot.hasData) {
return Text('No data available'); // Display a message when no data is available.
} else {
return Text(
'Latest Number: ${snapshot.data}',
style: TextStyle(fontSize: 24),
); // Display the latest number when data is available.
}
},
),
),
);
}
}
Here is the full Code of main.dart file
Dart
import 'dart:async';
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false, // Remove the debug banner
theme: ThemeData(
primarySwatch: Colors.green, // Set the app's primary theme color to green
),
title: 'StreamBuilder Example',
home: NumberStreamPage(),
);
}
}
class NumberStreamPage extends StatefulWidget {
@override
_NumberStreamPageState createState() => _NumberStreamPageState();
}
class _NumberStreamPageState extends State<NumberStreamPage> {
late StreamController<int> _numberStreamController;
@override
void initState() {
super.initState();
// Create a stream controller and add numbers to the stream.
_numberStreamController = StreamController<int>();
_startAddingNumbers(); // Start adding numbers to the stream.
}
void _startAddingNumbers() async {
for (int i = 0; i < 10; i++) {
await Future.delayed(Duration(seconds: 2)); // Delay for 2 seconds.
_numberStreamController.sink.add(i); // Add the number to the stream.
}
}
@override
void dispose() {
_numberStreamController.close(); // Close the stream when disposing.
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('StreamBuilder Example'),
),
body: Center(
child: StreamBuilder<int>(
stream: _numberStreamController.stream,
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator(); // Display a loading indicator when waiting for data.
} else if (snapshot.hasError) {
return Text('Error: ${snapshot.error}'); // Display an error message if an error occurs.
} else if (!snapshot.hasData) {
return Text('No data available'); // Display a message when no data is available.
} else {
return Text(
'Latest Number: ${snapshot.data}',
style: TextStyle(fontSize: 24),
); // Display the latest number when data is available.
}
},
),
),
);
}
}
Output:
Similar Reads
Non-linear Components In electrical circuits, Non-linear Components are electronic devices that need an external power source to operate actively. Non-Linear Components are those that are changed with respect to the voltage and current. Elements that do not follow ohm's law are called Non-linear Components. Non-linear Co
11 min read
Steady State Response In this article, we are going to discuss the steady-state response. We will see what is steady state response in Time domain analysis. We will then discuss some of the standard test signals used in finding the response of a response. We also discuss the first-order response for different signals. We
9 min read
Use Case Diagram - Unified Modeling Language (UML) A Use Case Diagram in Unified Modeling Language (UML) is a visual representation that illustrates the interactions between users (actors) and a system. It captures the functional requirements of a system, showing how different users engage with various use cases, or specific functionalities, within
9 min read
Half Wave Rectifier A Half-wave rectifier is an electronic device that is used to convert Alternating current (AC) to Direct current (DC). A half-wave rectifier allows either a positive or negative half-cycle of AC to pass and blocks the other half-cycle. Half-wave rectifier selectively allows only one half-cycle of th
15 min read
Flutter Tutorial This Flutter Tutorial is specifically designed for beginners and experienced professionals. It covers both the basics and advanced concepts of the Flutter framework.Flutter is Google’s mobile SDK that builds native Android and iOS apps from a single codebase. It was developed in December 2017. When
7 min read
What is Agile Methodology? The Agile methodology is a proper way of managing the project with breaking them into smaller phases which is iteration. It basically focus on flexibility of the project which we can change and improve the team work regularly as per requirements.Table of ContentWhat is Agile?What is the Agile Method
14 min read
How to Download and Install the Google Play Store The Google Play Store is the heartbeat of your Android experience—home to millions of apps, games, and updates that keep your device functional, fun, and secure. But what if your phone or tablet doesn’t have it pre-installed?In this step-by-step guide, you’ll learn how to safely download and install
6 min read
Top 8 Software Development Life Cycle (SDLC) Models used in Industry Software development models are various processes or methods that are chosen for project development depending on the objectives and goals of the project. Many development life cycle models have been developed to achieve various essential objectives. Models specify the various steps of the process a
9 min read
IEEE 802.11 Architecture The IEEE 802.11 standard, commonly known as Wi-Fi, outlines the architecture and defines the MAC and physical layer specifications for wireless LANs (WLANs). Wi-Fi uses high-frequency radio waves instead of cables for connecting the devices in LAN. Given the mobility of WLAN nodes, they can move unr
9 min read
Transaction in DBMS In a Database Management System (DBMS), a transaction is a sequence of operations performed as a single logical unit of work. These operations may involve reading, writing, updating, or deleting data in the database. A transaction is considered complete only if all its operations are successfully ex
10 min read