One of the calculation methods of flutter

counter.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  int _counter2 = 0;
  List<int?>? _counter3 = [];
  List<List<int?>?>? arraySt = [
    [null, 1, 2, null, 3, 3, 1, 2, 3, 4, 2, 2, 2]
  ];

  void _incrementCounter() {
    setState(() {
      check();
    });
  }

  List<bool?> d = [];

  void check() {
    _counter = arraySt
            ?.map((e) => e
                ?.where((element) => element == _counter2)
                .toList(growable: false))
            .map((element) {
          _counter3 = element ?? [];
          return element?.length;
        }).first ??
        0;
    if (_counter == 0) _counter2 = 0;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '$_counter3',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _counter2++;
          _incrementCounter();
        },
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

2022-06-08.1.34.34.mov