Initialization of StatefulWidget

We use a "stful" snippet.

import 'package:flutter/material.dart';

void main() {
  runApp(App());
}

class App extends StatefulWidget {
  const App({Key? key}) : super(key: key);

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  @override
  Widget build(BuildContext context) {
    return const Placeholder();
  }
}

Click counter example

import 'package:flutter/material.dart';

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

class App extends StatefulWidget {
  const App({Key? key}) : super(key: key);

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  int counter = 0;
  void onClick() {
    setState(() {
      counter = counter + 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: const Color(0xFFF4EDDB),
        body: Center(
            child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text('Click count',
                style: TextStyle(
                  fontSize: 30,
                )),
            Text(
              '$counter',
              style: const TextStyle(fontSize: 30),
            ),
            IconButton(
                iconSize: 50,
                onPressed: onClick,
                icon: const Icon(
                  Icons.add_box_sharp,
                ))
          ],
        )),
      ),
    );
  }
}

flutter update UI: setState is basically calling the 'build' method again with the new data.