createState and State
- Flutter course
- Beginner
- Lesson 22/99
- 4 min
Learn how createState produces the State object.
createState
The createState method of a StatefulWidget produces a State object when the widget is placed on screen. This State holds the widget's changing data for its entire lifetime. Flutter calls createState once each time the widget is inserted into the tree; the same State lives until the widget is removed.
class Sayac extends StatefulWidget {
const Sayac({super.key});
@override
State<Sayac> createState() => _SayacState();
}
class _SayacState extends State<Sayac> {
int deger = 0;
@override
Widget build(BuildContext context) {
return Text('$deger');
}
}State and setState
The State class holds the widget's variable data and build method. To change data you call setState; it marks the State as dirty and makes Flutter call build again. If you update a variable without setState, the screen does not refresh.
class _SayacState extends State<Sayac> {
int deger = 0;
void artir() {
setState(() {
deger = deger + 1;
});
}
@override
Widget build(BuildContext context) {
return Text('$deger');
}
}Practice Print createState info
In main, print two lines with print: createState uretir and state yasar.
Starter code
void main() {
// iki satır yazdır:
// createState uretir
// state yasar
}Sample solution
void main() {
print('createState uretir');
print('state yasar');
}Expected output
createState uretir state yasar
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 When is createState called?
- Once when the widget is first inserted into the tree Correct answer
- Every time the widget rebuilds
- Every time setState is called
- When the app closes
Explanation: createState is called once when the widget is first inserted into the tree and produces the State object; it does not repeat on every build.
2 createState method
@override
State<Sayac> ____() => _SayacState();@override
State<Sayac> createState() => _SayacState();Explanation: The createState method produces the State object for a StatefulWidget.
3 createState and State
| Term | Meaning |
|---|---|
createState |
Method that produces the State object |
State nesnesi |
Holds variable data |
setState |
Marks State as dirty |
_SayacState |
Implementer of the State class |