Flutter State and Stateless Widgets: The Building Blocks of Efficiency

As we embark on our journey to optimise the widget tree, the first pit stop is understanding the role of State and Stateless widgets in Flutter. These two types of widgets are the linchpins of any Flutter app, and knowing when to use which can dramatically affect your application’s performance and resource consumption.

Stateless widgets are immutable, meaning once you create them, you can’t change their properties. They are less resource-intensive and are perfect for parts of your UI that remain static. On the other hand, State widgets are dynamic and mutable, ideal for UI elements that need to be redrawn to reflect changes in data or user interaction.

In this section, we’ll delve into the nuances of these two widget types and reveal best practices for utilising them effectively in your widget tree. By the end, you’ll gain a solid understanding of how to strategically employ State and Stateless widgets to create not just an interactive, but also a highly optimised Flutter application.

Use stateless widgets whenever possible. Stateless widgets are more efficient than stateful widgets because they do not have to rebuild every time the state changes.

// Stateless widget example
class MyStatelessWidget extends StatelessWidget {
  final String text;

  MyStatelessWidget(this.text);

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

// Stateful widget example
class MyStatefulWidget extends StatefulWidget {
  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  String text = 'Hello, world!';

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

  void changeText() {
    setState(() {
      text = 'Goodbye, world!';
    });
  }
}        

In the stateless widget example, the MyStatelessWidget widget will only be rebuilt if its text property changes. However, in the stateful widget example, the MyStatefulWidget widget will be rebuilt every time the setState() method is called, even if the widget's text property does not change.

This is because stateful widgets need to maintain their own state, and the setState() method is used to notify Flutter that the state has changed. Flutter then rebuilds the widget and its descendants to reflect the new state.

Stateless widgets, on the other hand, do not need to maintain their own state. They simply render their UI based on the properties that are passed to them. This makes stateless widgets more efficient than stateful widgets.

In general, you should use stateless widgets whenever possible. This will improve the performance of your app and make it easier to maintain.