Lære What State Is and Why It Matters | Understanding State in Flutter

Definition

In Flutter, state is any piece of data that can change during the lifetime of the app and directly affects what is rendered on the screen.

The Flutter UI is always a reflection of the current state. When the state changes, Flutter rebuilds the affected widgets to display the updated data. This tight link between state and UI makes apps interactive and responsive to user actions.

Proper state management keeps the app consistent and predictable. If state is not handled correctly, the UI may fail to update when data changes, resulting in a confusing and unreliable user experience.

main.dart


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import 'package:flutter/material.dart';

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

class CounterApp extends StatelessWidget {
  const CounterApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: CounterScreen(),
    );
  }
}

class CounterScreen extends StatefulWidget {
  const CounterScreen({super.key});

  @override
  State<CounterScreen> createState() => _CounterScreenState();
}

class _CounterScreenState extends State<CounterScreen> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter = _counter + 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Counter Example')),
      body: Center(
        child: Text(
          'Counter value: �_counter',
          style: const TextStyle(fontSize: 24),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        child: const Icon(Icons.add),
      ),
    );
  }
}

This counter example demonstrates how state works in Flutter. The _counter variable holds the current state of the counter. When you press the floating action button, the _incrementCounter function is called. Inside this function, setState is used to update the _counter value. Calling setState tells Flutter that the state has changed, so it rebuilds the CounterScreen widget and updates the UI to display the new counter value. Without calling setState, the UI would not reflect the change. This pattern—storing data in state, updating it in response to user actions, and rebuilding the UI when state changes—is at the core of interactive Flutter apps.

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