Explain StatefulWidget vs StatelessWidget in Flutter.
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Perfect 👌 — this is one of the fundamental Flutter concepts you need to understand before building apps.
🔹 StatefulWidget vs StatelessWidget in Flutter
Flutter apps are built using Widgets (everything is a widget: text, button, screen, etc.).
The key difference lies in whether the UI depends on state (data that can change over time).
🟢 StatelessWidget
-
Definition: A widget that does not change once built.
-
It is immutable → its properties (data) are final and can’t change during runtime.
-
UI is fixed unless the widget is rebuilt from outside (e.g., parent provides new data).
Definition: A widget that does not change once built.
It is immutable → its properties (data) are final and can’t change during runtime.
UI is fixed unless the widget is rebuilt from outside (e.g., parent provides new data).
Example:
import 'package:flutter/material.dart';
class MyStatelessWidget extends StatelessWidget {
final String title;
MyStatelessWidget({required this.title});
@override
Widget build(BuildContext context) {
return Text(title, style: TextStyle(fontSize: 24));
}
}
import 'package:flutter/material.dart';
class MyStatelessWidget extends StatelessWidget {
final String title;
MyStatelessWidget({required this.title});
@override
Widget build(BuildContext context) {
return Text(title, style: TextStyle(fontSize: 24));
}
}
✅ The text shown will never change unless you rebuild the widget with a new title.
🟡 StatefulWidget
-
Definition: A widget that can change during runtime because it holds mutable state.
-
Consists of two classes:
-
StatefulWidget → immutable configuration.
-
State → mutable data that can be updated with setState().
-
When the state changes, the widget is rebuilt to reflect new data.
Definition: A widget that can change during runtime because it holds mutable state.
Consists of two classes:
-
StatefulWidget→ immutable configuration. -
State→ mutable data that can be updated withsetState().
When the state changes, the widget is rebuilt to reflect new data.
Example:
import 'package:flutter/material.dart';
class CounterWidget extends StatefulWidget {
@override
_CounterWidgetState createState() => _CounterWidgetState();
}
class _CounterWidgetState extends State<CounterWidget> {
int counter = 0;
void _incrementCounter() {
setState(() {
counter++; // UI will rebuild when counter changes
});
}
@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('Counter: $counter', style: TextStyle(fontSize: 24)),
ElevatedButton(
onPressed: _incrementCounter,
child: Text('Increment'),
),
],
);
}
}
import 'package:flutter/material.dart';
class CounterWidget extends StatefulWidget {
@override
_CounterWidgetState createState() => _CounterWidgetState();
}
class _CounterWidgetState extends State<CounterWidget> {
int counter = 0;
void _incrementCounter() {
setState(() {
counter++; // UI will rebuild when counter changes
});
}
@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('Counter: $counter', style: TextStyle(fontSize: 24)),
ElevatedButton(
onPressed: _incrementCounter,
child: Text('Increment'),
),
],
);
}
}
✅ Each time you press the button, counter updates and the UI changes dynamically.
🔑 Key Differences
| Feature | StatelessWidget 🟢 | StatefulWidget 🟡 |
|---|---|---|
| State | Immutable | Mutable (can change) |
| Rebuilds | Only if parent sends new data | Rebuilds when setState() is called |
| Use Case | Static text, icons, styles | Forms, counters, animations, user input |
| Performance | Faster (less overhead) | Slightly heavier (maintains state) |
✅ Simple Rule of Thumb
-
Use StatelessWidget when the UI never changes.
-
Use StatefulWidget when the UI must update dynamically based on user interaction or data changes.
Use StatelessWidget when the UI never changes.
Use StatefulWidget when the UI must update dynamically based on user interaction or data changes.
👉 Do you want me to also show you a real-world example combining both (like a StatefulWidget button that updates a StatelessWidget label)?
Read More
What is Flutter and why use it for app development?
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