flutter - Setstate is not working in my calculator app in flutter

Question

I am new to flutter development and recently started my first working app : "The Calculator". But, I think, my setstate is not working. Here's the code. Please help.

ignore_for_file: avoid_types_as_parameter_names, non_constant_identifier_names, prefer_const_constructors, prefer_const_literals_to_create_immutables

import 'package:flutter/material.dart';

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

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

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

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    String init = '0';
    var res = '';
    var operationToPerform = '0';
    var firstNum = 0;
    var secondNum = 0;

    _Calc(var got) {
      if (got == 'AC') {
        init = '0';
        res = '0';
        firstNum = 0;
        operationToPerform = '0';
        secondNum = 0;
      } else if (got == 'C') {
        firstNum = 0;
        secondNum = 0;
      } else if (got == '+' ||
          got == '-' ||
          got == '/' ||
          got == '*' ||
          got == '%') {
        firstNum = int.parse(init);
        res = '';
        operationToPerform = got;
      } else if (got == '=') {
        secondNum = int.parse(init);
        if (operationToPerform == '+') {
          res = (firstNum + secondNum).toString();
        }
        if (operationToPerform == '-') {
          res = (firstNum - secondNum).toString();
        }
        if (operationToPerform == '*') {
          res = (firstNum * secondNum).toString();
        }
        if (operationToPerform == '/') {
          res = (firstNum / secondNum).toString();
        }
        if (operationToPerform == '%') {
          res = ((firstNum / secondNum) * 100).toString();
        }
      } else {
        res = int.parse(init + got).toString();
      }
      setState(() {
        init = res;
      });
    }

    Widget Numbutton(var num, [var color = Colors.black, var text]) {
      return Container(
        decoration: BoxDecoration(boxShadow: [
          BoxShadow(
            color: Colors.grey.shade900,
            offset: Offset(2, 2),
            blurRadius: 15,
            spreadRadius: 1,
          ),
          BoxShadow(
            color: Colors.grey.shade700,
            offset: Offset(2, 2),
            blurRadius: 15,
            spreadRadius: 1,
          )
        ], shape: BoxShape.circle),
        child: ElevatedButton(
          onPressed: () {
            _Calc(num);
          },
          child: Text(
            num,
            style: TextStyle(
              fontSize: 25,
              fontWeight: FontWeight.w300,
              color: text,
            ),
          ),
          style: ElevatedButton.styleFrom(
              shape: CircleBorder(), primary: color, fixedSize: Size(40, 40)),
        ),
      );
    }

    Widget OpButton(var text) {
      return ElevatedButton(
        onPressed: () {
          _Calc(text);
        },
        child: Text(
          text,
          style: TextStyle(fontSize: 15, fontWeight: FontWeight.w400),
        ),
        style: ElevatedButton.styleFrom(
          primary: Colors.grey.shade900,
        ),
      );
    }

    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        backgroundColor: Colors.black,
        body: Wrap(
          direction: Axis.horizontal,
          alignment: WrapAlignment.spaceEvenly,
          children: <Widget>[
            Column(
              children: <Widget>[
                SizedBox(
                  height: 220,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.end,
                  children: [
                    Text(
                      init,
                      style: TextStyle(
                        color: Colors.grey.shade500,
                      ),
                    )
                  ],
                ),
                SizedBox(
                  height: 10,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.end,
                  children: <Widget>[
                    Text(
                      init,
                      style:
                          TextStyle(color: Colors.grey.shade400, fontSize: 50),
                    ),
                  ],
                ),
                SizedBox(
                  height: 50,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: <Widget>[
                    OpButton('AC'),
                    OpButton('C'),
                    Numbutton('<', Colors.grey.shade300, Colors.grey.shade900),
                    Numbutton('%', Colors.grey.shade300, Colors.grey.shade900),
                  ],
                ),
                SizedBox(
                  height: 20,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: <Widget>[
                    Numbutton('7'),
                    Numbutton('8'),
                    Numbutton('9'),
                    Numbutton(
                      '*',
                      Colors.grey.shade300,
                      Colors.grey.shade900,
                    ),
                  ],
                ),
                SizedBox(
                  height: 20,
                ),
                Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: <Widget>[
                      Numbutton('4'),
                      Numbutton('5'),
                      Numbutton('6'),
                      Numbutton(
                          '+', Colors.grey.shade300, Colors.grey.shade900),
                    ]),
                SizedBox(
                  height: 20,
                ),
                Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: <Widget>[
                      Numbutton('1'),
                      Numbutton('2'),
                      Numbutton('3'),
                      Numbutton(
                          '-', Colors.grey.shade300, Colors.grey.shade900),
                    ]),
                SizedBox(
                  height: 20,
                ),
                Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: <Widget>[
                      Numbutton('00'),
                      Numbutton('0'),
                      Numbutton('.'),
                      Numbutton(
                          '/', Colors.grey.shade300, Colors.grey.shade900),
                    ])
              ],
            )
          ],
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            _Calc('=');
          },
          child: Icon(Icons.arrow_forward_ios_rounded),
          backgroundColor: Colors.grey.shade900,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
      ),
    );
  }
}

I had tried doing that like init +=res;

The flutter version and dart version I am using is

Flutter 2.5.0 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 4cc385b4b8 (5 days ago) • 2021-09-07 23:01:49 -0700
Engine • revision f0826da7ef
Tools • Dart 2.14.0

I have tried restarting android studio and the android emulator, nothing seems to work.

标签： flutterdart

Answer 1

请将此初始化代码移出构建方法

String init = '0';
    var res = '';
    var operationToPerform = '0';
    var firstNum = 0;
    var secondNum = 0;

我已修改您的代码。请尝试一次

import 'package:flutter/material.dart';
    
    void main() {
      runApp(const MyApp());
    }
    
    class MyApp extends StatefulWidget {
      const MyApp({Key? key}) : super(key: key);
    
      @override
      _MyAppState createState() => _MyAppState();
    }
    
    class _MyAppState extends State<MyApp> {
 String init = '0';
        var res = '';
        var operationToPerform = '0';
        var firstNum = 0;
        var secondNum = 0;
      @override
      Widget build(BuildContext context) {
       
    
        _Calc(var got) {
          if (got == 'AC') {
            init = '0';
            res = '0';
            firstNum = 0;
            operationToPerform = '0';
            secondNum = 0;
          } else if (got == 'C') {
            firstNum = 0;
            secondNum = 0;
          } else if (got == '+' ||
              got == '-' ||
              got == '/' ||
              got == '*' ||
              got == '%') {
            firstNum = int.parse(init);
            res = '';
            operationToPerform = got;
          } else if (got == '=') {
            secondNum = int.parse(init);
            if (operationToPerform == '+') {
              res = (firstNum + secondNum).toString();
            }
            if (operationToPerform == '-') {
              res = (firstNum - secondNum).toString();
            }
            if (operationToPerform == '*') {
              res = (firstNum * secondNum).toString();
            }
            if (operationToPerform == '/') {
              res = (firstNum / secondNum).toString();
            }
            if (operationToPerform == '%') {
              res = ((firstNum / secondNum) * 100).toString();
            }
          } else {
            res = int.parse(init + got).toString();
          }
          setState(() {
            init = res;
          });
        }
    
        Widget Numbutton(var num, [var color = Colors.black, var text]) {
          return Container(
            decoration: BoxDecoration(boxShadow: [
              BoxShadow(
                color: Colors.grey.shade900,
                offset: Offset(2, 2),
                blurRadius: 15,
                spreadRadius: 1,
              ),
              BoxShadow(
                color: Colors.grey.shade700,
                offset: Offset(2, 2),
                blurRadius: 15,
                spreadRadius: 1,
              )
            ], shape: BoxShape.circle),
            child: ElevatedButton(
              onPressed: () {
                _Calc(num);
              },
              child: Text(
                num,
                style: TextStyle(
                  fontSize: 25,
                  fontWeight: FontWeight.w300,
                  color: text,
                ),
              ),
              style: ElevatedButton.styleFrom(
                  shape: CircleBorder(), primary: color, fixedSize: Size(40, 40)),
            ),
          );
        }
    
        Widget OpButton(var text) {
          return ElevatedButton(
            onPressed: () {
              _Calc(text);
            },
            child: Text(
              text,
              style: TextStyle(fontSize: 15, fontWeight: FontWeight.w400),
            ),
            style: ElevatedButton.styleFrom(
              primary: Colors.grey.shade900,
            ),
          );
        }
    
        return MaterialApp(
          debugShowCheckedModeBanner: false,
          home: Scaffold(
            backgroundColor: Colors.black,
            body: Wrap(
              direction: Axis.horizontal,
              alignment: WrapAlignment.spaceEvenly,
              children: <Widget>[
                Column(
                  children: <Widget>[
                    SizedBox(
                      height: 220,
                    ),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.end,
                      children: [
                        Text(
                          init,
                          style: TextStyle(
                            color: Colors.grey.shade500,
                          ),
                        )
                      ],
                    ),
                    SizedBox(
                      height: 10,
                    ),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.end,
                      children: <Widget>[
                        Text(
                          init,
                          style:
                              TextStyle(color: Colors.grey.shade400, fontSize: 50),
                        ),
                      ],
                    ),
                    SizedBox(
                      height: 50,
                    ),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                      children: <Widget>[
                        OpButton('AC'),
                        OpButton('C'),
                        Numbutton('<', Colors.grey.shade300, Colors.grey.shade900),
                        Numbutton('%', Colors.grey.shade300, Colors.grey.shade900),
                      ],
                    ),
                    SizedBox(
                      height: 20,
                    ),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                      children: <Widget>[
                        Numbutton('7'),
                        Numbutton('8'),
                        Numbutton('9'),
                        Numbutton(
                          '*',
                          Colors.grey.shade300,
                          Colors.grey.shade900,
                        ),
                      ],
                    ),
                    SizedBox(
                      height: 20,
                    ),
                    Row(
                        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                        children: <Widget>[
                          Numbutton('4'),
                          Numbutton('5'),
                          Numbutton('6'),
                          Numbutton(
                              '+', Colors.grey.shade300, Colors.grey.shade900),
                        ]),
                    SizedBox(
                      height: 20,
                    ),
                    Row(
                        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                        children: <Widget>[
                          Numbutton('1'),
                          Numbutton('2'),
                          Numbutton('3'),
                          Numbutton(
                              '-', Colors.grey.shade300, Colors.grey.shade900),
                        ]),
                    SizedBox(
                      height: 20,
                    ),
                    Row(
                        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                        children: <Widget>[
                          Numbutton('00'),
                          Numbutton('0'),
                          Numbutton('.'),
                          Numbutton(
                              '/', Colors.grey.shade300, Colors.grey.shade900),
                        ])
                  ],
                )
              ],
            ),
            floatingActionButton: FloatingActionButton(
              onPressed: () {
                _Calc('=');
              },
              child: Icon(Icons.arrow_forward_ios_rounded),
              backgroundColor: Colors.grey.shade900,
            ),
            floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
          ),
        );
      }
    }