practice flutter course

import 'dart:math';

import 'package:flutter/material.dart';

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

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

  @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 a = 0, b = 0, c = 0;

  static List<double> calculate(int a, int b, int c) {
    double discr = (b*b - 4*a*c).toDouble();
    if (discr < 0) throw Exception();

    if(discr > 0) {
      double x1 = (-b + sqrt(discr)) / 2 * a;
      double x2 = (-b - sqrt(discr)) / 2 * a;
      return [x1, x2];
    } else {
      double x1 = (-b) / 2 * a;
      return [x1];
    }
  }

  String check() {
    try {
      List n = calculate(a,b,c);
      return n.toString();
    } catch(e) {
      return 'Некорректное уравнение!';
    }
  }

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      initialIndex: 0,
      length: 2,
      child: Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
          bottom: const TabBar(
            tabs: <Widget>[
              Tab(
                icon: Text('Calculate')
              ),
              Tab(
                icon: Text('Result')
              ),
            ],
          ),
        ),
        body: TabBarView(
          children: <Widget>[
            Center(
              child: Container(
                child: Column(
                  children: [
                    Align(
                      alignment: Alignment.centerLeft,
                      child: Text('Ваше уравнение:', style: TextStyle(fontSize: 30),),
                    ),
                    Text('$a*x^2 + $b*x + $c = 0'),
                    Row(
                      children: [
                        Expanded(
                          flex: 1,
                          child: TextField(
                            onChanged: (t) {setState(() {a = int.parse(t);});},
                          ),
                        ),
                        Expanded(
                          flex: 1,
                          child: TextField(
                            onChanged: (t) {setState(() {b = int.parse(t);});},
                          ),
                        ),
                        Expanded(
                          flex: 1,
                          child: TextField(
                            onChanged: (t) {setState(() {c = int.parse(t);});},
                          ),
                        ),
                      ],
                    )
                  ],
                ),
              ),
            ),
            Center(
              child: Text(check()),
            ),
          ],
        ),
      )
    );
  }
}