main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    home: Home(),
  ));
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  TextEditingController weightController = TextEditingController();
  TextEditingController heightController = TextEditingController();

  GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  String _infoText = 'Informe seus dados';

  void _resetFields(){
    weightController.text = '';
    heightController.text = '';
    setState(() {
      _infoText = 'Informe seus dados';
      _formKey = GlobalKey<FormState>();
    });
  }

  void _calculate(){
    setState(() {
      double weight = double.parse(weightController.text);
      double height = double.parse(heightController.text) / 100;

      double imc = weight / (height * height);
      String imcString = imc.toStringAsPrecision(4);

      if(imc < 18.6) {
        _infoText = 'Abaixo do Peso($imcString)';
      } else if (imc >= 18.6 && imc < 24.9) {
        _infoText = 'Peso Ideal ($imcString)';
      } else if (imc >= 24.9 && imc < 29.9) {
        _infoText = 'Levemente acima do peso ($imcString)';
      } else if (imc >= 29.9 && imc < 34.9) {
        _infoText = 'Obesidade grau I ($imcString)';
      } else if (imc > 34.9 && imc <= 39.9) {
        _infoText = 'Obesidade grau II ($imcString)';
      } else if (imc >= 40) {
        _infoText = 'Obesidade grau III ($imcString)';
      }
    });
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Calculadora de IMC'),
        centerTitle: true,
        backgroundColor: Colors.green,
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.refresh),
            onPressed: _resetFields ,
          )
        ],
      ),
      backgroundColor: Colors.white,
      body: SingleChildScrollView(
        padding: EdgeInsets.fromLTRB(10.0, 0.0, 10.0, 0.0),
        child: Form(
          key: _formKey,
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              Icon(Icons.person_outline, size: 120.0, color: Colors.green),
              TextFormField(
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                    labelText: 'Peso (kg)',
                    labelStyle: TextStyle(color: Colors.green)),
                textAlign: TextAlign.center,
                style: TextStyle(color: Colors.green, fontSize: 25.0),
                controller: weightController,
                validator: (value) {
                  if(value.isEmpty){
                    return 'Insira seu peso';
                  }
                  return null;
                },
              ),
              TextFormField(
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                    labelText: 'Altura (cm)',
                    labelStyle: TextStyle(color: Colors.green)),
                textAlign: TextAlign.center,
                style: TextStyle(color: Colors.green, fontSize: 25.0),
                controller: heightController,
                validator: (value) {
                  if(value.isEmpty){
                    return 'Insira sua altura';
                  }
                  return null;
                },
              ),
              Padding(
                padding: EdgeInsets.only(top: 10.0, bottom: 10.0),
                child: Container(
                    height: 50.0,
                    child: RaisedButton(
                      onPressed: () {
                        if(_formKey.currentState.validate()){
                          _calculate();
                        }
                      },
                      child: Text('Calcular', style: TextStyle(color: Colors.white, fontSize: 25.0),),
                      color: Colors.green,
                    )
                ),
              ),
              Text(_infoText,
                textAlign: TextAlign.center,
                style: TextStyle(color: Colors.green, fontSize: 25.0),
              )
            ],
          ),
        )
      )
    );
  }
}