【赠书第7期】从零基础到精通Flutter开发

在学习任何新技术时，理论知识是基础，实践项目是提升。以下是一个简单的Flutter项目，用于创建一个简单的计算器应用程序。

import 'package:flutter/material.dart';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CalculatorHome(),
    );
  }
}
 
class CalculatorHome extends StatefulWidget {
  @override
  _CalculatorHomeState createState() => _CalculatorHomeState();
}
 
class _CalculatorHomeState extends State<CalculatorHome> {
  String _result = "0";
  String _operation = "";
  bool _clearNeeded = false;
 
  void _clear() {
    setState(() {
      _result = "0";
      _operation = "";
      _clearNeeded = false;
    });
  }
 
  void _operationPressed(String operation) {
    setState(() {
      if (_operation != "") {
        _result = _calculate(_result, _operation);
      }
      _operation = operation;
      _clearNeeded = true;
    });
  }
 
  void _digitPressed(String digit) {
    setState(() {
      if (_clearNeeded) {
        _result = digit;
        _clearNeeded = false;
      } else if (_result == "0") {
        _result = digit;
      } else {
        _result += digit;
      }
    });
  }
 
  String _calculate(String a, String operation) {
    var calc = Calculator();
    switch (operation) {
      case '+':
        return calc.add(double.parse(a), double.parse(_result)).toString();
      case '-':
        return calc.subtract(double.parse(a), double.parse(_result)).toString();
      case '*':
        return calc.multiply(double.parse(a), double.parse(_result)).toString();
      case '/':
        if (_result != "0") {
          return calc.divide(double.parse(a), double.parse(_result)).toString();
        } else {
          return "Can't divide by 0";
        }
      default:
        return "Error";
    }
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              _result,
              style: TextStyle(
                fontSize: 32.0,
                color: Colors.black,
              ),
            ),
            Row(
              mainAxisAlignment: MainAxisAlign