main.dart

import 'package:flutter/material.dart';

main() => runApp(MinimalStatefulApp());

class MinimalStatefulApp extends StatefulWidget {
  @override
  _MinimalState createState() => _MinimalState();
}

class _MinimalState extends State<MinimalStatefulApp> {

  int _counter = 0;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onDoubleTap: () => setState(() => _counter++),
      child: Center(
        child: Text(
          'Counter: $_counter',
          textDirection: TextDirection.ltr,
        ),
      ),
    );
  }
}