State and counter

Define the counter variable with StatefulWidget.

State and counter variable

To hold the counter value, you use a StatefulWidget. In the State class you define a variable like int _count = 0;. This variable is private to State, and when changed with setState, the screen is rebuilt.

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

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

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

Updating with setState

To change the counter variable, setState is called. setState runs the code inside and rebuilds the widget. This way widgets such as Text('$_count') show the current value.

setState(() {
  _count = _count + 1;
});

Exercise Increment counter and print

Write a StatefulWidget named SayacEkrani; define an int counter variable in its State (starting at 0). Write a function artir that increments the counter by 1 inside setState and prints the counter value. In main, create a State instance and call artir.

Show example solution

import 'package:flutter/material.dart';

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

  @override
  State<SayacEkrani> createState() => _SayacEkraniState();
}

class _SayacEkraniState extends State<SayacEkrani> {
  int _sayac = 0;

  void artir() {
    setState(() {
      _sayac = _sayac + 1;
    });
    print(_sayac);
  }
}

void main() {
  final state = _SayacEkraniState();
  state.artir();
}

Test yourself

What type is the variable holding the counter value?
- bool
- int
- double
- String
Show answer

int — Since the counter value is an integer, it is kept as int; String, bool or double are not for this purpose.

Add the counter variable type

class _SayacEkraniState extends State<SayacEkrani> {
  ____ _sayac = 0;
}

Show answer

class _SayacEkraniState extends State<SayacEkrani> {
  int _sayac = 0;
}

State and counter parts

StatefulWidget

Widget type holding state
int

Counter's type
setState

Rebuilds the screen
_sayac

Counter variable in State

Next lesson: Increment button

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