Understanding Stateless and Stateful Widgets in Flutter

Flutter is a framework for building fast and beautiful apps for iOS, Android, and the web. Widgets are the building blocks used to create Flutter apps. There are two types of widgets in Flutter: stateless and stateful. In this guide, we will look at the difference between these two widget types and when to use them.

Stateless Widgets

A stateless widget is a widget that cannot be redrawn dynamically. Once it is built, it remains the same until it is destroyed. This means that any changes to the widget must be made by rebuilding the widget.

Stateless widgets are used to display information that does not change over time. They are also useful for building UI elements that do not require user interaction, such as text, images, and icons. Stateless widgets are lightweight and fast because they do not need to manage their state.

Here is an example of building a stateless widget in Flutter:

import 'package:flutter/material.dart';

class MyText extends StatelessWidget {
  final String text;

  MyText(this.text);

  @override
  Widget build(BuildContext context) {
    return Text(text);
  }
}

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In this example, we build a MyText widget that displays a given text. The text variable is passed in the constructor of the widget, and the build method returns the Text widget that displays the text value.

Stateful Widgets

A stateful widget is a widget that can be redrawn dynamically. It holds mutable state that can be updated over time. When the state of a stateful widget changes, the widget is rebuilt to reflect the new state.

Stateful widgets are used when building UI elements that require user interaction, such as forms, buttons, and custom widgets that change their display depending on their state. They are also useful when displaying data that changes over time, such as live data from an API.

Here is an example of building a stateful widget in Flutter:

import 'package:flutter/material.dart';

class MyCounter extends StatefulWidget {
  @override
  _MyCounterState createState() => _MyCounterState();
}

class _MyCounterState extends State<MyCounter> {
  int count = 0;

  void increment() {
    setState(() {
      count++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('Count: $count'),
        RaisedButton(
          onPressed: increment,
          child: Text('Increment'),
        ),
      ],
    );
  }
}

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In this example, we build a MyCounter widget that displays a count and a button to increment the count. The count variable is stored in the state of the widget, and the increment method is used to update the state when the button is pressed. The build method returns a Column widget that displays the count and the button.

Conclusion

Understanding the difference between stateless and stateful widgets is important when building Flutter apps. Stateless widgets are used to display information that does not change, while stateful widgets are used for UI elements that require user interaction or live data. By choosing the right type of widget for your needs, you can build fast and responsive Flutter apps.