BMIを算出するFlutter Application

README.md

BMI Calc

パターンマッチングを使いたくなって 夜しか眠れなくなってしまったので 遊びがてら書いてみました

DartPad

https://dartpad.dev/82452362f8fcd41b638a9f320d287696

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const App());

class App extends StatelessWidget {
  const App({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: const HomePage(),
      theme: ThemeData.light(useMaterial3: true),
      darkTheme: ThemeData.dark(useMaterial3: true),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text("BMI Calc")),
      body: const Padding(
        padding: EdgeInsets.all(16),
        child: HomePageBody(),
      ),
    );
  }
}

class HomePageBody extends StatefulWidget {
  const HomePageBody({super.key});

  @override
  State<HomePageBody> createState() => _HomePageBodyState();
}

class _HomePageBodyState extends State<HomePageBody> {
  double? _height;
  double? _weight;

  @override
  Widget build(BuildContext context) {
    final bmi = switch ((_height, _weight)) {
      (double height, double weight) => weight / (height * height),
      _ => null,
    };
    final obesityType = switch (bmi) {
      double _ => Obesity.fromBmi(bmi),
      _ => null,
    };
    final obesityColor = switch (obesityType) {
      Obesity.low => Colors.blue,
      Obesity.standard => Colors.green,
      Obesity.obesity1 => Colors.yellow,
      Obesity.obesity2 => Colors.orange,
      Obesity.obesity3 => Colors.red,
      Obesity.obesity4 => Colors.purple,
      _ => Colors.grey,
    };

    /// 適正体重
    final properWeight = switch (_height) {
      double height => height * height * 22,
      _ => null,
    };

    final textTheme = Theme.of(context).textTheme;

    final resultWidget = AnimatedSwitcher(
      duration: const Duration(milliseconds: 100),
      child: DecoratedBox(
        key: ValueKey(obesityType),
        decoration: BoxDecoration(
          color: obesityColor,
          borderRadius: BorderRadius.circular(8),
        ),
        child: Padding(
          padding: const EdgeInsets.all(16),
          child: Column(
            children: [
              Text(
                switch ((bmi, obesityType)) {
                  (double bmi, Obesity obesityType) =>
                    '${bmi.toStringAsFixed(2)} ${obesityType.name}',
                  _ => "入力してください",
                },
                style: textTheme.displaySmall!.copyWith(
                  fontWeight: FontWeight.bold,
                ),
              ),
              const SizedBox(height: 16),
              if (properWeight != null)
                Text(
                  '適正体重: ${properWeight.toStringAsFixed(2)}kg',
                  style: textTheme.titleLarge,
                ),
            ],
          ),
        ),
      ),
    );

    return Column(
      children: [
        const Text("身長(m)を入力してください"),
        TextFormField(
          onChanged: (String value) =>
              setState(() => _height = double.tryParse(value)),
          decoration: const InputDecoration(
            border: OutlineInputBorder(),
            hintText: "身長(m)を入力してください",
          ),
          keyboardType: const TextInputType.numberWithOptions(decimal: true),
        ),
        const SizedBox(height: 16),
        const Text("体重(kg)を入力してください"),
        TextFormField(
          onChanged: (String value) =>
              setState(() => _weight = double.tryParse(value)),
          decoration: const InputDecoration(
            border: OutlineInputBorder(),
            hintText: "体重(kg)を入力してください",
          ),
          keyboardType: const TextInputType.numberWithOptions(decimal: true),
        ),
        const SizedBox(height: 16),
        resultWidget,
      ],
    );
  }
}

/// 日本肥満学会の定義による肥満度の判定
enum Obesity {
  /// 低体重
  low,

  /// 標準体重
  standard,

  /// 肥満(1度)
  obesity1,

  /// 肥満(2度)
  obesity2,

  /// 肥満(3度)
  obesity3,

  /// 肥満(4度)
  obesity4,
  ;

  /// BMIから肥満度を判定する
  static Obesity fromBmi(double bmi) => switch (bmi) {
        < 18.5 => Obesity.low,
        < 25 => Obesity.standard,
        < 30 => Obesity.obesity1,
        < 35 => Obesity.obesity2,
        < 40 => Obesity.obesity3,
        _ => Obesity.obesity4,
      };
  String get name => switch (this) {
        Obesity.low => "低体重",
        Obesity.standard => "標準体重",
        Obesity.obesity1 => "肥満(1度)",
        Obesity.obesity2 => "肥満(2度)",
        Obesity.obesity3 => "肥満(3度)",
        Obesity.obesity4 => "肥満(4度)",
      };
}