Dart语言基础

Dart是Google开发的面向对象的编程语言，专为客户端优化，是Flutter框架的开发语言。本章将介绍Dart语言的核心特性和基础语法。

Dart语言概述

Dart特性

Dart是一种现代、面向对象的语言，具有以下特性：

强类型系统（可选类型）
面向对象编程
函数是一等公民
支持异步编程
垃圾回收机制
单线程事件循环

dart

// 简单的Dart程序示例
void main() {
  print('Hello, Dart!');
  
  // 变量声明
  String name = 'Flutter Developer';
  int age = 25;
  double score = 95.5;
  bool isActive = true;
  
  print('Name: $name, Age: $age, Score: $score, Active: $isActive');
}

变量和数据类型

变量声明

dart

void variableExample() {
  // var - 类型由编译器推断
  var userName = 'John Doe';
  var userAge = 30;
  
  // final - 运行时初始化的常量
  final String email = 'john@example.com';
  final List<String> hobbies = ['reading', 'swimming'];
  
  // const - 编译时常量
  const String appName = 'MyApp';
  const List<String> platforms = ['Android', 'iOS', 'Web', 'Desktop'];
  
  // dynamic - 动态类型
  dynamic value = 'This is a string';
  value = 42; // 可以更改为其他类型
  
  print('User: $userName, Email: $email');
}

数据类型

dart

void dataTypeExample() {
  // 数值类型
  int integerNum = 42;
  double doubleNum = 3.14159;
  num mixedNum = 10; // 可以是int或double
  
  // 字符串类型
  String singleLine = 'This is a single line string.';
  String multiLine = '''
  This is a 
  multi-line string.
  ''';
  
  String interpolation = 'The answer is ${integerNum + doubleNum}';
  
  // 布尔类型
  bool isTrue = true;
  bool isFalse = false;
  
  // 列表（数组）
  List<String> fruits = ['apple', 'banana', 'orange'];
  List<int> numbers = [1, 2, 3, 4, 5];
  var dynamicList = [1, 'hello', true]; // 混合类型列表
  
  // 集合（Set）
  Set<String> uniqueItems = {'red', 'green', 'blue'};
  
  // 映射（Map）
  Map<String, dynamic> person = {
    'name': 'John',
    'age': 30,
    'isMarried': false,
  };
  
  print('Interpolated: $interpolation');
  print('Fruits: $fruits');
  print('Person: $person');
}

函数

函数声明

dart

// 基本函数
String greet(String name) {
  return 'Hello, $name!';
}

// 箭头函数（单表达式）
int square(int x) => x * x;

// 可选参数
String buildFullName(String firstName, String lastName, [String? middleName]) {
  if (middleName != null) {
    return '$firstName $middleName $lastName';
  }
  return '$firstName $lastName';
}

// 命名参数
void configureApp({String? theme, bool? darkMode, int? fontSize}) {
  print('Theme: $theme, Dark Mode: $darkMode, Font Size: $fontSize');
}

// 默认参数值
String formatCurrency(double amount, {String currency = 'USD'}) {
  return '${currency}\$${amount.toStringAsFixed(2)}';
}

// 函数作为参数
void executeWithCallback(Function callback) {
  print('Before callback');
  callback();
  print('After callback');
}

void functionExample() {
  print(greet('Alice'));
  print(square(5));
  print(buildFullName('John', 'Doe', 'Middle'));
  print(formatCurrency(123.45));
  
  configureApp(theme: 'Material', darkMode: true);
  
  executeWithCallback(() {
    print('This is the callback function');
  });
}

匿名函数和闭包

dart

void anonymousFunctionExample() {
  // 匿名函数
  var multiply = (int a, int b) {
    return a * b;
  };
  
  print('Multiply: ${multiply(5, 3)}');
  
  // 闭包
  int multiplier = 10;
  
  Function createMultiplier(int factor) {
    return () {
      return multiplier * factor;
    };
  }
  
  var doubleMultiplier = createMultiplier(2);
  print('Double multiplier result: ${doubleMultiplier()}');
  
  // Lambda表达式
  List<int> numbers = [1, 2, 3, 4, 5];
  List<int> doubled = numbers.map((n) => n * 2).toList();
  print('Original: $numbers, Doubled: $doubled');
}

控制流

条件语句

dart

void controlFlowExample() {
  int score = 85;
  
  // if-else语句
  if (score >= 90) {
    print('Grade: A');
  } else if (score >= 80) {
    print('Grade: B');
  } else if (score >= 70) {
    print('Grade: C');
  } else {
    print('Grade: F');
  }
  
  // switch语句
  String day = 'Monday';
  switch (day) {
    case 'Saturday':
    case 'Sunday':
      print('Weekend');
      break;
    case 'Monday':
    case 'Tuesday':
    case 'Wednesday':
    case 'Thursday':
    case 'Friday':
      print('Weekday');
      break;
    default:
      print('Unknown day');
  }
  
  // 三元运算符
  String status = score >= 60 ? 'Passed' : 'Failed';
  print('Status: $status');
  
  // 逻辑运算符
  bool isAdult = true;
  bool hasLicense = true;
  bool canDrive = isAdult && hasLicense;
  print('Can drive: $canDrive');
}

循环语句

dart

void loopExample() {
  // for循环
  for (int i = 0; i < 5; i++) {
    print('For loop: $i');
  }
  
  // for-in循环
  List<String> items = ['apple', 'banana', 'orange'];
  for (String item in items) {
    print('Item: $item');
  }
  
  // while循环
  int counter = 0;
  while (counter < 3) {
    print('While loop: $counter');
    counter++;
  }
  
  // do-while循环
  int doCounter = 0;
  do {
    print('Do-while loop: $doCounter');
    doCounter++;
  } while (doCounter < 2);
  
  // break和continue
  for (int i = 0; i < 10; i++) {
    if (i == 3) continue; // 跳过3
    if (i == 7) break;    // 在7处停止
    print('Loop with control: $i');
  }
}

面向对象编程

类和对象

dart

// 基本类定义
class Person {
  String name;
  int age;
  String email;
  
  // 构造函数
  Person(this.name, this.age, this.email);
  
  // 命名构造函数
  Person.adult(String name, String email) : this(name, 18, email);
  
  // 工厂构造函数
  factory Person.fromMap(Map<String, dynamic> map) {
    return Person(
      map['name'] ?? '',
      map['age'] ?? 0,
      map['email'] ?? '',
    );
  }
  
  // 方法
  void introduce() {
    print('Hi, I am $name, $age years old.');
  }
  
  // getter和setter
  String get displayName => 'Mr./Ms. $name';
  
  set setName(String newName) {
    if (newName.length > 2) {
      name = newName;
    }
  }
}

// 继承
class Student extends Person {
  String school;
  double gpa;
  
  Student(String name, int age, String email, this.school, this.gpa)
      : super(name, age, email);
  
  @override
  void introduce() {
    super.introduce();
    print('I study at $school with GPA: $gpa');
  }
  
  void study() {
    print('$name is studying hard.');
  }
}

// 抽象类
abstract class Animal {
  String name;
  
  Animal(this.name);
  
  // 抽象方法
  void makeSound();
  
  // 具体方法
  void eat() {
    print('$name is eating.');
  }
}

// 实现接口
class Dog extends Animal {
  Dog(String name) : super(name);
  
  @override
  void makeSound() {
    print('$name says Woof!');
  }
}

void oopExample() {
  // 创建对象
  Person person = Person('John Doe', 25, 'john@example.com');
  person.introduce();
  print('Display name: ${person.displayName}');
  
  Student student = Student('Jane Smith', 20, 'jane@example.com', 'MIT', 3.8);
  student.introduce();
  student.study();
  
  Dog dog = Dog('Buddy');
  dog.eat();
  dog.makeSound();
}

Mixin

dart

// Mixin定义
mixin Flyable {
  void fly() {
    print('Flying...');
  }
  
  void land() {
    print('Landing...');
  }
}

mixin Swimmable {
  void swim() {
    print('Swimming...');
  }
}

// 使用Mixin
class Duck extends Animal with Flyable, Swimmable {
  Duck(String name) : super(name);
  
  @override
  void makeSound() {
    print('$name says Quack!');
  }
}

void mixinExample() {
  Duck duck = Duck('Donald');
  duck.makeSound();
  duck.fly();
  duck.swim();
  duck.land();
}

异步编程

Future和异步函数

dart

// 异步函数
Future<String> fetchData() async {
  await Future.delayed(Duration(seconds: 2));
  return 'Data fetched successfully!';
}

Future<void> asyncExample() async {
  print('Start fetching data...');
  
  try {
    String result = await fetchData();
    print(result);
  } catch (e) {
    print('Error: $e');
  }
}

// Future的链式调用
void futureChainExample() {
  Future<String> getData() {
    return Future.delayed(Duration(seconds: 1), () => 'Hello');
  }
  
  getData()
    .then((value) => '$value World!')
    .then((value) => print(value))
    .catchError((error) => print('Error: $error'));
}

// 并发执行多个Future
Future<void> concurrentExample() async {
  Future<String> fetchUserOrder() {
    return Future.delayed(Duration(seconds: 2), () => 'Large Latte');
  }
  
  Future<String> fetchUserInfo() {
    return Future.delayed(Duration(seconds: 1), () => 'John Doe');
  }
  
  // 同时执行
  var results = await Future.wait([
    fetchUserOrder(),
    fetchUserInfo(),
  ]);
  
  print('Order: ${results[0]}, User: ${results[1]}');
}

Stream

dart

Stream<int> countStream() async* {
  for (int i = 1; i <= 5; i++) {
    await Future.delayed(Duration(milliseconds: 500));
    yield i;
  }
}

void streamExample() {
  countStream().listen(
    (value) => print('Stream value: $value'),
    onDone: () => print('Stream completed'),
    onError: (error) => print('Stream error: $error'),
  );
}

泛型

dart

// 泛型类
class Container<T> {
  T? value;
  
  Container(this.value);
  
  T? getValue() => value;
  
  void setValue(T newValue) {
    value = newValue;
  }
}

// 泛型方法
T getFirstElement<T>(List<T> list) {
  if (list.isEmpty) throw ArgumentError('List is empty');
  return list.first;
}

// 泛型约束
class NumberProcessor<T extends num> {
  T value;
  
  NumberProcessor(this.value);
  
  T multiplyByTwo() {
    return (value * 2) as T;
  }
}

void genericExample() {
  // 使用泛型类
  Container<String> stringContainer = Container('Hello');
  Container<int> intContainer = Container(42);
  
  print('String: ${stringContainer.getValue()}');
  print('Int: ${intContainer.getValue()}');
  
  // 使用泛型方法
  List<String> names = ['Alice', 'Bob', 'Charlie'];
  String first = getFirstElement(names);
  print('First name: $first');
  
  // 使用泛型约束
  NumberProcessor<int> processor = NumberProcessor(10);
  print('Multiplied: ${processor.multiplyByTwo()}');
}

异常处理

dart

void exceptionExample() {
  try {
    int result = 10 ~/ 0; // 会产生异常
  } on IntegerDivisionByZeroException {
    print('Cannot divide by zero!');
  } catch (e) {
    print('An error occurred: $e');
  } finally {
    print('This will always execute');
  }
  
  // 抛出异常
  try {
    validateAge(-5);
  } catch (e) {
    print('Caught exception: $e');
  }
}

void validateAge(int age) {
  if (age < 0) {
    throw ArgumentError('Age cannot be negative');
  }
}

扩展方法

dart

// 扩展方法
extension StringExtension on String {
  bool get isValidEmail {
    return RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$').hasMatch(this);
  }
  
  String get capitalize {
    if (isEmpty) return this;
    return this[0].toUpperCase() + substring(1).toLowerCase();
  }
  
  int get wordCount {
    return split(RegExp(r'\s+')).length;
  }
}

void extensionExample() {
  String email = 'test@example.com';
  print('Is valid email: ${email.isValidEmail}');
  
  String name = 'john doe';
  print('Capitalized: ${name.capitalize}');
  
  String sentence = 'This is a sample sentence';
  print('Word count: ${sentence.wordCount}');
}

注解

dart

// 常用注解
class ApiResponse {
  @deprecated
  String oldField = '';
  
  @override
  String toString() => 'ApiResponse';
  
  @required // 需要导入foundation
  String requiredField = '';
}

// 自定义注解
class Configurable {
  final String name;
  final String description;
  
  const Configurable(this.name, this.description);
}

class AppConfig {
  @Configurable('theme', 'Application theme setting')
  String theme = 'light';
  
  @Configurable('language', 'Application language')
  String language = 'en';
}

Dart与Flutter集成

在Flutter中使用Dart特性

dart

import 'package:flutter/material.dart';

class DartFeaturesDemo extends StatefulWidget {
  @override
  _DartFeaturesDemoState createState() => _DartFeaturesDemoState();
}

class _DartFeaturesDemoState extends State<DartFeaturesDemo> {
  List<Map<String, dynamic>> _users = [];
  bool _isLoading = false;

  @override
  void initState() {
    super.initState();
    _loadUsers();
  }

  // 异步加载数据
  Future<void> _loadUsers() async {
    setState(() {
      _isLoading = true;
    });

    try {
      // 模拟网络请求
      await Future.delayed(Duration(seconds: 2));
      
      // 使用Dart的列表和映射特性
      _users = [
        {'id': 1, 'name': 'Alice Johnson', 'email': 'alice@example.com'},
        {'id': 2, 'name': 'Bob Smith', 'email': 'bob@example.com'},
        {'id': 3, 'name': 'Carol Davis', 'email': 'carol@example.com'},
      ];
    } catch (e) {
      print('Error loading users: $e');
    } finally {
      setState(() {
        _isLoading = false;
      });
    }
  }

  // 使用扩展方法格式化数据
  String _formatUserName(String name) {
    return name.split(' ').map((word) => 
      word[0].toUpperCase() + word.substring(1).toLowerCase()
    ).join(' ');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Dart Features in Flutter'),
      ),
      body: _isLoading
          ? Center(child: CircularProgressIndicator())
          : ListView.builder(
              itemCount: _users.length,
              itemBuilder: (context, index) {
                final user = _users[index];
                return Card(
                  margin: EdgeInsets.symmetric(horizontal: 16, vertical: 8),
                  child: ListTile(
                    leading: CircleAvatar(
                      child: Text(user['name'][0]),
                    ),
                    title: Text(_formatUserName(user['name'])),
                    subtitle: Text(user['email']),
                    trailing: Icon(Icons.arrow_forward_ios),
                  ),
                );
              },
            ),
      floatingActionButton: FloatingActionButton(
        onPressed: _loadUsers,
        child: Icon(Icons.refresh),
      ),
    );
  }
}

最佳实践

代码风格和规范

dart

// 1. 使用final声明不可变变量
class UserProfile {
  final String id;
  final String name;
  final String email;
  final DateTime createdAt;

  // 2. 使用命名构造函数提高可读性
  UserProfile({
    required this.id,
    required this.name,
    required this.email,
    DateTime? createdAt,
  }) : createdAt = createdAt ?? DateTime.now();

  // 3. 使用工厂构造函数处理复杂初始化
  factory UserProfile.fromJson(Map<String, dynamic> json) {
    return UserProfile(
      id: json['id'] as String,
      name: json['name'] as String,
      email: json['email'] as String,
      createdAt: DateTime.parse(json['created_at'] as String),
    );
  }

  // 4. 使用getter进行计算属性
  String get displayName => name.split(' ')[0];

  bool get isEmailValid {
    return RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$').hasMatch(email);
  }

  // 5. 实现toString方法便于调试
  @override
  String toString() {
    return 'UserProfile(id: $id, name: $name, email: $email)';
  }
}

Dart语言是Flutter开发的基础，掌握其核心概念和特性对于成为优秀的Flutter开发者至关重要。通过理解变量、函数、面向对象编程、异步编程等概念，可以更好地构建高质量的Flutter应用。

Dart语言基础 #

Dart语言概述 #

Dart特性 #

变量和数据类型 #

变量声明 #

数据类型 #

函数 #

函数声明 #

匿名函数和闭包 #

控制流 #

条件语句 #

循环语句 #

面向对象编程 #

类和对象 #

Mixin #

异步编程 #

Future和异步函数 #

Stream #

泛型 #

异常处理 #

扩展方法 #

注解 #

Dart与Flutter集成 #

在Flutter中使用Dart特性 #

最佳实践 #

代码风格和规范 #

Dart语言基础

Dart语言概述

Dart特性

变量和数据类型

变量声明

数据类型

函数

函数声明

匿名函数和闭包

控制流

条件语句

循环语句

面向对象编程

类和对象

Mixin

异步编程

Future和异步函数

Stream

泛型

异常处理

扩展方法

注解

Dart与Flutter集成

在Flutter中使用Dart特性

最佳实践

代码风格和规范