TapTap source code: NullBreaker CTF

import 'package:flutter/material.dart';

// Author: @odinshell

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'RevIt',
      theme: ThemeData(
        primarySwatch: Colors.red,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'NullbreakerCTF 2020'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  int i = 0;
  String _flag = "";
  String _status = "Sup?";
  int ord;

  void _incrementCounter() {
    setState(() {
      _counter++;
      if(_counter > 400){
        _status = "Nice, Keep going";
        if(_counter > 700){
          _status = "You're almost there!";
        }
      }
      if(_counter > 850){
        var secret = ['\xa7', '\xab', '\xca', '\xbd', '\xcf', '\x92', ']', '\xa7', '\xcd', '\x9b', 'Y', '\xa0', '\xcd', '\xb6', '\xaf', 'X', '\x9c', '^', '^', 'Z', '\x9b', '\xb6', '\x9b', 'Z', '\x9f', 'Z', '\x9b', '\xba', 'X', '\xa7', '\xce', '\x94'];
        if(_flag == ""){
          for(i = 0; i < secret.length; i++){
            ord = (secret[i].codeUnits[0] + 1200) ^ 1337;
            _flag = _flag + new String.fromCharCode(ord);
          }
        }
      } else {
        _flag = "";
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '$_status',
              style: Theme.of(context).textTheme.headline4,
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline5,
            ),
            Text(
              '$_flag',
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}