bmi_calculator_app/lib/calculator.dart

import 'package:flutter/material.dart';

import 'result.dart';

class CalculatorPage extends StatefulWidget {
  CalculatorPage({Key? key}) : super(key: key);
  final String title = 'BMI Calculator';
  static const routeName = '/';

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

class _CalculatorPageState extends State<CalculatorPage> {
  double _weight = 60;
  double _height = 165;
  double _age = 18;
  int _gender = 0; // male = 1; female = 0

  @override
  void initState() {
    super.initState();
  }

  int bodyMassIndex() => ((_weight / (_height * _height)) * 10000).round();

  int bodyFatPercentage() =>
      (1.2 * bodyMassIndex() + .23 * _age - 10.8 * _gender - 5.4).round();

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: <Widget>[
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: <Widget>[
                  Expanded(
                    child: Ink(
                      decoration: const ShapeDecoration(
                        color: Colors.lightGreen,
                        shape: CircleBorder(),
                      ),
                      child: IconButton(
                        icon: const Icon(Icons.female),
                        tooltip: 'Choose female gender',
                        onPressed: () {
                          setState(() => _gender = 0);
                        },
                        color: Colors.white,
                      ),
                    ),
                  ),
                  Expanded(
                    child: Ink(
                      decoration: const ShapeDecoration(
                        color: Colors.lightGreen,
                        shape: CircleBorder(),
                      ),
                      child: IconButton(
                        icon: const Icon(Icons.male),
                        tooltip: 'Choose male gender',
                        onPressed: () {
                          setState(() => _gender = 1);
                        },
                        color: Colors.white,
                      ),
                    ),
                  ),
                ],
              ),
              Text('Weight'),
              Text("${_weight.round().toString()} kg"),
              Slider(
                value: _weight,
                min: 0,
                max: 100,
                divisions: 100,
                label: _weight.round().toString(),
                onChanged: (double value) => setState(() => _weight = value),
              ),
              Text('Height'),
              Text("${_height.round().toString()} cm"),
              Slider(
                value: _height,
                min: 100,
                max: 200,
                divisions: 100,
                label: _height.round().toString(),
                onChanged: (double value) => setState(() => _height = value),
              ),
              Text('Age'),
              Text("${_age.round().toString()} years old"),
              Slider(
                value: _age,
                min: 10,
                max: 100,
                divisions: 100,
                label: _age.round().toString(),
                onChanged: (double value) => setState(() => _age = value),
              ),
              ElevatedButton(
                onPressed: () {
                  print(
                      "BMI: ${bodyMassIndex()};  BFP: ${bodyFatPercentage()}");
                  Navigator.pushNamed(
                    context,
                    ResultPage.routeName,
                    arguments: Results(bodyMassIndex(), bodyFatPercentage()),
                  );
                },
                child: Text('Calculate'),
              ),
            ],
          ),
        ),
      );
}