import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Example(),
      ),
    );
  }
}

class Example extends StatefulWidget {
  @override
  _ExampleState createState() => _ExampleState();
}

class _ExampleState extends State<Example> {
  int _counter = 0;

  Widget _weNeedItOnlyOnce() {
    print('_weNeedItOnlyOnce');
    return Padding(
      padding: EdgeInsets.all(32),
      child: Text('Просто немного текста'),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
        padding: EdgeInsets.all(32),
        child: Column(
          children: [
            FlatButton(
              color: Colors.blue,
              child: Text(
                'Счетчик: $_counter',
                style: TextStyle(color: Colors.white),
              ),
              onPressed: () {
                setState(() {
                  _counter++;
                });
              },
            ),
            _weNeedItOnlyOnce(),
            const WeNeedItOnlyOnce(),
          ],
        ));
  }
}

class WeNeedItOnlyOnce extends StatelessWidget {
  const WeNeedItOnlyOnce();

  @override
  Widget build(BuildContext context) {
    print('WeNeedItOnlyOnce');
    return Padding(
      padding: EdgeInsets.all(32),
      child: Text('Просто немного текста 2'),
    );
  }
}