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Difference Between Stateless and Stateful Widgets in Flutter

In Flutter, widgets are the building blocks of the user interface. They are categorized into two types:

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1. StatelessWidget

• StatelessWidget does not change its state during its lifetime.

• It is immutable, meaning its properties (data) cannot be changed after the widget is created.

• Used for static UI components, like text, images, or buttons, where the content remains the same.

Example of StatelessWidget

Copyimport 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text("Stateless Example")),
        body: const Center(
          child: MyStatelessWidget(),
        ),
      ),
    );
  }
}

class MyStatelessWidget extends StatelessWidget {
  const MyStatelessWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text(
      "I am a StatelessWidget",
      style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
    );
  }
}

Output:
The text "I am a StatelessWidget" is displayed. It does not change during the app's lifecycle.

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2. StatefulWidget

• StatefulWidget can change its state during its lifetime.

• It is mutable, meaning it can hold and update data.

• Used for interactive or dynamic UI components, like buttons, sliders, text fields, and counters.

Example of StatefulWidget

Copyimport 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text("Stateful Example")),
        body: const Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _counter = 0; // Variable that holds the state

  void _incrementCounter() {
    setState(() {
      _counter++; // Update the state
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(
          "Counter: $_counter",
          style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
        ),
        const SizedBox(height: 10),
        ElevatedButton(
          onPressed: _incrementCounter,
          child: const Text("Increment Counter"),
        ),
      ],
    );
  }
}

Output:

• The app shows "Counter: 0" initially.

• Every time you press the "Increment Counter" button, the counter value increases by 1, and the UI updates.

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Key Differences Summary

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When to Use Which?

• Use StatelessWidget if the UI does not need to change.

• Use StatefulWidget if the UI needs to update based on user interaction or data changes.