A Counter Up and Down

Part of the Making It Interactive section of Coddy's Flutter journey. Lesson 13 of 34.

A function can live inside the State class too. There it can read the State's variables and call setState:

void _increase() {
  setState(() {
    _count++;
  });
}

_count++ is short for _count = _count + 1, and _count-- takes one away. A function that belongs to a class is called a method, and a private one starts with _, like the variables.

Hand it to a button by its name, with no parentheses, as in Your Own Functions: IconButton(icon: Icon(Icons.add), onPressed: _increase).

Challenge

Easy

The counter only goes up. Add a method _decrease that takes one away inside setState, and an IconButton with Icons.remove before the number that calls it.

Try it yourself

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: HomePage(),
    );
  }
}

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

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _count = 0;

  void _increase() {
    setState(() {
      _count++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Counter')),
      body: Center(
        child: Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text('$_count', style: TextStyle(fontSize: 48)),
            IconButton(icon: Icon(Icons.add), onPressed: _increase),
          ],
        ),
      ),
    );
  }
}