BMI 계산기 - 버튼값 설정하기

1. HomePage에서 관리되어야 할 변수 확인

• 성별 (bool)

• 키 (double)

• 몸무게 (double)

2. HomePage StatefulWidget으로 변경 후 변수 선언

1. class HomePage를 StatefulWidget으로 변경

// 변경 전
class HomePage extends StatelessWidget { // `HomePage` 위에 커서를 올려놓고 ctrl+. , `Convert to StatefulWidget` 선택
  @override
  Widget build(BuildContext context) {

// 변경 후
class HomePage extends StatefulWidget {
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {

2. 상속 받은 클래스에 변수 선언 및 변경 시 실행될 함수를 정의

class HomePage extends StatefulWidget {
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool isMale = true;
  void onGenderChanged(bool male) {
    setState(() {
      isMale = male;
    });
  }

  double height = 170;
  void onHeightChanged(double newHeight) {
    setState(() {
      height = newHeight;
    });
  }

  double weight = 70;
  void onWeightChanged(double newWeight) {
    setState(() {
      weight = newWeight;
    });
  }

  @override
  Widget build(BuildContext context) {

3. 변수를 각각의 위젯에 넘겨주기
1. GenderBox
1. HomePage에 선언된 변수를 GenderBox에 연결하기.
• 변수 연결 → bool isMale;
• 함수 연결 → void Function(bool newValue) 타입으로 연결.

// 변경 전
import 'package:flutter/material.dart';

class GenderBox extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        gender(context, Icons.male, "MALE", true),
        SizedBox(width: 8),
        gender(context, Icons.female, "FEMALE", false),
      ],
    );
  }

// 변경 후
import 'package:flutter/material.dart';

class GenderBox extends StatelessWidget {
  GenderBox(this.isMale, this.onChanged);

  bool isMale;
  void Function(bool newValue) onChanged;

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        gender(context, Icons.male, "MALE", isMale),
        SizedBox(width: 8),
        gender(context, Icons.female, "FEMALE", !isMale),
      ],
    );
  }

2. Widget gender에서 “터치 시 값이 바뀌도록” 세팅
• GestureDetector 세팅 : Container에 Wrap with Widget → onTap → onChanged 연결
• onChanged가 받을 수 있는 변수 설정: bool isMaleBox

// 변경 전
Widget gender(
    BuildContext context,
    IconData icon,
    String text,
    bool selected,
  ) {
    return Expanded(
      child: Container(
        height: 150,
        decoration: BoxDecoration(
          border: Border.all(color: Theme.of(context).dividerColor),
        ),
        child: Stack(
          children: [
            Positioned(
              top: 10,
              left: 10,
              child: Opacity(opacity: 0.3, child: Icon(icon, size: 80)),
            ),
            Positioned(
              right: 20,
              bottom: 20,
              child: Opacity(
                opacity: selected ? 1 : 0.3,
                child: Text(
                  text,
                  style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

// 변경 후
Widget gender(
    BuildContext context,
    IconData icon,
    String text,
    bool selected,
    /*bool isMaleBox,*/
  ) {
    return Expanded(
      child: /*GestureDetector(
        onTap: () {
          onChanged(isMaleBox);
        },
        child: */Container(
          height: 150,
          decoration: BoxDecoration(
            border: Border.all(color: Theme.of(context).dividerColor),
          ),
          child: Stack(
            children: [
              Positioned(
                top: 10,
                left: 10,
                child: Opacity(opacity: 0.3, child: Icon(icon, size: 80)),
              ),
              Positioned(
                right: 20,
                bottom: 20,
                child: Opacity(
                  opacity: selected ? 1 : 0.3,
                  child: Text(
                    text,
                    style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

3. bool isMaleBox가 추가되었으므로 생성자에도 그 자리를 마련.

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        gender(context, Icons.male, "MALE", isMale, /*true*/),
        SizedBox(width: 8),
        gender(context, Icons.female, "FEMALE", !isMale, /*false*/),
      ],
    );
  }

2. HomePage의 GenderBox 내에 변수 할당하기

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("BMI CALCULATOR"), centerTitle: true),
      body: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 50),
        child: Column(
          children: [
            GenderBox(/*isMale, onGenderChanged*/),
            Spacer(),
            SliderBox(label: 'HEIGHT', value: 170, unit: 'cm'),
            Spacer(),
            SliderBox(label: 'WEIGHT', value: 70, unit: 'kg'),
            Spacer(),
            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(onPressed: () {}, child: Text("CALCULATE")),
            ),
          ],
        ),
      ),
    );
  }
}

3. HomePage의 SliderBox 내에 변수 할당하기

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("BMI CALCULATOR"), centerTitle: true),
      body: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 50),
        child: Column(
          children: [
            GenderBox(isMale, onGenderChanged),
            Spacer(),
            SliderBox(label: 'HEIGHT', value: /*height*/, unit: 'cm'),
            Spacer(),
            SliderBox(label: 'WEIGHT', value: /*weight*/, unit: 'kg'),
            Spacer(),
            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(onPressed: () {}, child: Text("CALCULATE")),
            ),
          ],
        ),
      ),
    );
  }
}

4. SliderBox에서 onHeightChanged와 onWeightChanged의 함수를 받을 수 있도록 void Function 타입의 변수 추가

import 'package:flutter/material.dart';

class SliderBox extends StatelessWidget {
  SliderBox({
    required this.label,
    required this.value,
    required this.unit,
    /*required this.onChanged,*/
  });

  String label;
  double value;
  String unit;
  /*void Function(double newValue) onChanged;*/

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Row(
          crossAxisAlignment: CrossAxisAlignment.end,
          children: [
            Text(label, style: TextStyle(fontSize: 20)),
            Spacer(),
            Text(
              value.toStringAsFixed(0),
              style: TextStyle(fontSize: 30, fontWeight: FontWeight.bold),
            ),
            Text(unit, style: TextStyle(fontSize: 20)),
          ],
        ),
        Slider(value: value, onChanged: /*onChanged*/, min: 1, max: 300),
      ],
    );
  }
}

5. HomePage의 SliderBox 내에 변수 추가
• 변수명: onChanged ← void Function 타입이므로 함수를 호출해야 함.
• 변수를 통해 호출할 함수명: onHeightChanged , onWeightChanged

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("BMI CALCULATOR"), centerTitle: true),
      body: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 50),
        child: Column(
          children: [
            GenderBox(isMale, onGenderChanged),
            Spacer(),
            SliderBox(
              label: 'HEIGHT',
              value: height,
              unit: 'cm',
              /*onChanged: onHeightChanged,*/
            ),
            Spacer(),
            SliderBox(
              label: 'WEIGHT',
              value: weight,
              unit: 'kg',
              /*onChanged: onWeightChanged,*/
            ),
            Spacer(),
            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(onPressed: () {}, child: Text("CALCULATE")),
            ),
          ],
        ),
      ),
    );
  }
}