【Flutter】電卓・計算機アプリの作成 3

double.parse()を使用して、文字列をdoubleに解析できます

it-swarm.dev

contains(Object element) → bool
Returns true if the collection contains an element equal to element. [...]

List class(公式)

add(E value) → void
Adds value to the end of this list, extending the length by one. [...]

List class(公式)

clear() → void
Removes all objects from this list; the length of the list becomes zero. [...]

List class(公式)

import 'dart:async';
import 'package:flutter/material.dart';
import 'calculation.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
        return MaterialApp(
            home: Scaffold(
                body: Column(
                    mainAxisAlignment: MainAxisAlignment.start,
                    children: [
                        TextField(),
                        Keyboard(),
                    ],
                )
            )
        );
    }
}
//==============================================================================
// 表示
class TextField extends StatefulWidget {
    _TextFiledState createState() => _TextFiledState();
}
class _TextFiledState extends State<TextField> {
    String _expression = '';

    void _UpdateText(String letter){
        setState(() {
            if(letter == 'C')
                _expression = '';
            else if (letter == '='){
                _expression='';
                var ans = Calculator.Execute();
                controller.sink.add(ans);
            }else if (letter == 'e'){
                _expression = 'Error';
            }
            else
                _expression += letter;
        });
    }

    @override
    Widget build(BuildContext context) {
        return Expanded(
            flex: 1,
            child: Container(
                child: Align(
                    alignment: Alignment.centerRight,
                    child: Text(
                        _expression,
                        style: TextStyle(
                            fontSize: 64.0,
                        ),
                    ),
                ),
            )
        );
    }

    static final controller = StreamController<String>.broadcast();
    @override
    void initState() {
        controller.stream.listen((event) => _UpdateText(event));
        controller.stream.listen((event) => Calculator.GetKey(event));
    }
}
//==============================================================================
// キーボード
class Keyboard extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
        return Expanded(
            flex: 2,
            child: Center(
                child: Container(
                    color: const Color(0xff87cefa),
                    child: GridView.count(
                        crossAxisCount: 4,
                        mainAxisSpacing: 3.0,
                        crossAxisSpacing: 3.0,
                        children: [
                            '7', '8', '9', '÷',
                            '4', '5', '6', '×',
                            '1', '2', '3', '-',
                            'C', '0', '=', '+',
                        ].map((key) {
                            return GridTile(
                                child: Button(key),
                            );
                        }).toList(),
                    ),
                )
            )
        );
    }
}
// キーボタン
class Button extends StatelessWidget {
    final _key;
    Button(this._key);
    @override
    Widget build(BuildContext context) {
        return Container(
            child: FlatButton(
                child: Center(
                    child: Text(
                        _key,
                        style: TextStyle(
                            fontSize: 46.0,
                            color: Colors.black54,
                        ),
                    ),
                ),
                onPressed: (){
                    _TextFiledState.controller.sink.add(_key);
                },
            )
        );
    }
}

const c_op = ['+', '-', '×', '÷'];

class Calculator{
    static var _number = new List();
    static var _op = new List();

    static String _buffer;
    static void GetKey(String letter){
        // 四則演算子
        if(c_op.contains(letter)){
            _op.add(letter);
            _number.add(double.parse(_buffer));
            _buffer = '';
        } // C
        else if(letter == 'C'){
            _number.clear();
            _op.clear();
            _buffer = '';
        } // =
        else if(letter == '='){
            return null;
        }// 数字
        else{
            _buffer += letter;
        }
    }

    static double _result;
    static String Execute() {
        _number.add(double.parse(_buffer));

        if (_number.length == 0)
            return '0';

        _result = _number[0];
        for (int i = 0; i < _op.length; i++) {
            if (_op[i] == '+')
                _result += _number[i + 1];
            else if (_op[i] == '-')
                _result -= _number[i + 1];
            else if (_op[i] == '×')
                _result *= _number[i + 1];
            else if (_op[i] == '÷' && _number[i + 1] != 0)
                _result /= _number[i + 1];
            else
                return 'e';
        }

        _number.clear();
        _op.clear();
        _buffer = '';

        var resultStr = _result.toString().split('.');
        return resultStr[1] == '0' ? resultStr[0] : _result.toString();
    }
}