What is Widgets in Flutter? - GeeksforGeeks (2024)

Flutter is Google’s UI toolkit for crafting beautiful, natively compiled iOS and Android apps from a single code base. To build any application we start with widgets – The building block of Flutter applications. Widgets describe what their view should look like given their current configuration and state. It includes a text widget, row widget, column widget, container widget, and many more.

What are Widgets?

Each element on the screen of the Flutter app is a widget. The view of the screen completely depends upon the choice and sequence of the widgets used to build the apps. And the structure of the code of apps is a tree of widgets.

Category of Widgets

There are mainly 14 categories into which the flutter widgets are divided. They are mainly segregated on the basis of the functionality they provide in a flutter application.

Types of Widgets

There are broadly two types of widgets in the flutter:

• Stateless Widget
• Stateful Widget

1. Stateless Widget

Stateless Widget is a type of widget which once built , then it’s properties and state can’t be changed. These widgets are immutable, once created can’t be modified.

Note: These are used for static content or UI content that don’t need a change after time.

Key Characterstics of Stateless Widgets are: Immutable , No State and Lightweight.

Examples: Display Text , Icons, Images, etc.

2. Stateful Widget

Stateful Widgets is a type of widget that can change state. It can maintain and update the appearance in the response to change in state.

Note: These are used for dynamic change in the properties and appearance over the time.

Key Characterstics of Stateful Widgets are: Mutable State , State Lifecycle and Dynamic Updates.

Examples: Buttons, Sliders, Text Fields, etc.

Implementation of Stateful and Stateless Widgets

Below is the Image with showing the Layout Tree:

Description of the widgets used are as follows:

• Scaffold – Implements the basic material design visual layout structure.
• App-Bar – To create a bar at the top of the screen.
• Text To write anything on the screen.
• Container – To contain any widget.
• Center – To provide center alignment to other widgets.

Example: The Layout Tree of basic app screen using Stateless Widgets:

import 'package:flutter/material.dart';void main() => runApp(const MyApp());// MyApp is the root widget of the applicationclass MyApp extends StatelessWidget { const MyApp({Key? key}) : super(key: key); @override Widget build(BuildContext context) { return const MaterialApp( home: HomePage(), ); }}// HomePage is the main screen of the appclass HomePage extends StatefulWidget { const HomePage({Key? key}) : super(key: key); @override _HomePageState createState() => _HomePageState();}class _HomePageState extends State<HomePage> { @override Widget build(BuildContext context) { return Scaffold( // Set the background color of the scaffold backgroundColor: Colors.lightGreen, appBar: AppBar( // Set the background color of the app bar backgroundColor: Colors.green, // Set the title of the app bar title: const Text("GeeksforGeeks"), ), // The main body of the scaffold body: const Center( // Display a centered text widget child: Text( "Hello Geeks!!", // Apply text styling style: TextStyle( fontSize: 24, // Set font size fontWeight: FontWeight.bold, // Set font weight ), ), ), ); }}

Example: The Layout Tree of basic app screen using Stateful Widgets. This also produces the same results as the above code.

import 'package:flutter/material.dart';void main() => runApp(const MyApp());class MyApp extends StatefulWidget { const MyApp({Key? key}) : super(key: key); @override // ignore: library_private_types_in_public_api _MyAppState createState() => _MyAppState();}class _MyAppState extends State<MyApp> { @override Widget build(BuildContext context) { return MaterialApp( home: Scaffold( backgroundColor: Colors.lightGreen, appBar: AppBar( backgroundColor: Colors.green, title: const Text("GeeksforGeeks"), ), // AppBar body: const Center( child: Text("Hello Geeks!!"), ), // Container ), // Scaffold );// MaterialApp }}

Output: