本文更新于2024-12-22，使用Dart 2.18.2。

可以使用dart run FILENAME运行程序文件。

关键字

• abstract
• as
• assert
• async
• await
• break
• case
• catch
• class
• const
• continue
• covariant
• default
• deferred
• do
• dynamic
• else
• enum
• export
• extends
• external
• factory
• false
• final
• finally
• for
• get
• hide
• if
• implements
• import
• in
• interface
• is
• library
• mixin
• new
• null
• on
• operator
• part
• rethrow
• return
• set
• show
• static
• super
• switch
• sync
• this
• throw
• true
• try
• typedef
• var
• void
• while
• with
• yield

常量

const声明的是编译时常量。

cosnt s1 = "";
const String s2 = "";

final s3 = "";
final String s4 = "";

var list = const[1, 2, 3];
const list = [1, 2, 3];

var dog = const Dog();
const dog = Dog();

变量

var a1;
var a2 = null;
dynamic a3;
dynamic a4 = "";

var s1 = "";
String s2 = "";

基本数据类型

数值

• int: 64位。范围为[-2^63 ~ 2^{63-1]。编译为JavaScript时使用JavaScript的范围[-2}53 ~ 2^53-1]。
• double：64位。范围约为[-1.7E308 ~ 1.7E308]。

字符串

使用UTF-16编码。

var s1 = '\'';
var s2 = "\"";

var s3 = '''1
2''';
var s4 = """1
2""";

var s5 = "\u2665\u{1f47b}";

var a1 = '$s1 ${s2}';
var a2 = "$s1 ${s2}";
var a3 = s1 + " " + s2;
var a4 = s1 * 3;
var a5 = "${s1+s2}";

布尔

var b1 = true;
bool b2 = false;

列表

var l = [1, "2", 1];

集合

var s = {1, "2"};

映射

var m1 = {};
var m2 = {
	"a": 1,
	"b": "2"
};

运算符

运算符优先级

从高到低依次为：

算数运算符

关系运算符

类型判定运算符

赋值运算符

逻辑运算符

位运算符

条件运算符

访问运算符

流程控制

条件语句

if-else

if (condition1) {
} else if (condition2) {
} else {
}

switch-case

switch (v) {
	case 1:
	case 2:
		print("");
		break;
	default:
}

循环语句

for

for (var i = 0; i < n; i++) {
}

for-in

for (var v in set) {
}

while

while (condition) {
}

do-while

do {
} while(condition);

break语句

switch (v) {
	case 1:
	case 2:
		print("");
		break;
	default:
}

for (var i = 0; i < n; i++) {
	break;
	print(i);
}

continue语句

for (var i = 0; i < n; i++) {
	if (i == 0) {
		continue;
	}
	print(i);
}

断言

断言只在开发（Checked）模式下有效，在生产（Production）模式下无效。

assert(flag);

异常

try {
	throw new Exception();
} on RangeError {
	rethrow;
} catch (e) {
} finally {
}

函数

String join(String a, String b) {
	return a + b;
}

add(a, b) {
	return a + b;
}

run() {
}

var s = join("a", "b");
var n = add(1, 2);
var a = run();

箭头函数

String join(String a, String b) => a + b;

可选位置参数

String join(String a, String b, [String c = "", String d = ""]) {
	return a + b + c + d;
}

var s = join("a", "b", "c");

可选命名参数

String join(String a, String b, {String c: "", d: ""}) {
	return a + b + c + d;
}

var s = join("a", "b", c: "c");

闭包

Function hello(String name) {
	var say = () {
		print("Hello $name");
	};
	return say;
}

var say = hello("Tom");
say();

主函数

void main(List<String> args) {
}

类

成员变量/实例变量

class Person {
	String name = "";
	int age = 0;
}

getter和setter

会为每个成员变量自动生成getter方法，对于非final修饰的成员变量也会自动生成setter方法。

class Person {
	String name = "";
	
	String get Name {
		return name;
	}

	set Name(String n) {
		name = n;
	}
}

var p = new Person();
p.Name = "Tom";
print(p.Name);

静态变量/类变量

class Person {
	String name = "";
	int age = 0;

	static int total = 1000;
	static Person me = new Person();
}

print(Person.total);

构造函数

构造函数的执行顺序为：实例变量赋值 -> 初始化参数列表 -> 父类构造函数 -> 本类构造函数。

默认无参构造函数

class Person {
	String name = "";
	int age = 0;
}

var p1 = new Person();
var p2 = Person();

默认自动生成无参构造函数：

	Person() {
	}

显式声明构造函数

class Person {
	String name = "";
	int age = 0;
	
	Person(String name, int age) {
		this.name = name;
		this.age = age;
	}
}

var p = new Person("Tom", 10);

命名构造函数

class Person {
	String name = "";
	int age = 0;
	
	Person.myself(age) {
		name = "Tom";
		this.age = age;
	}
}

var p = new Person.myself(10);

构造函数简写

class Person {
	String name = "";
	int age = 0;
	
	Person(this.name, this.age);
	
	Person.create(this.name, {this.age: 0});
}

class Student extends Person {
	String number = "";

	Student(super.name, super.age);
}

var p1 = new Person("Tom", 10);
var p2 = new Person.create("Tom", age: 10);

var s = new Student("Tom", 10);

初始化列表

class Person {
	String name = "";
	int age = 0;
	
	Person.myself(int age): name = "Tom", this.age = age {
	}
}

var p = new Person.myself(10);

重定向构造函数

class Person {
	String name = "";
	int age = 0;
	
	Person(this.name, this.age);
	
	Person.myself(int age): this("Tom", age);
}

var p = new Person.myself(10);

常量构造函数

class Person {
	final String name;
	final int age;
	
	const Person(this.name, this.age);
}

var p1 = new Person("Tom", 10);
var p2 = const Person("Tom", 10);

工厂方法的构造函数

class Person {
	String name = "";
	int age = 0;
	
	static Map<String, Person> _people = {};
	
	Person(this.name, this.age);
	
	factory Person.Tom() {
		var name = "Tom";
		var p = _people[name];
		if (p == null) {
			p = Person(name, 0);
			_people[name] = p;
		}
		return p;
	}
}

var p = new Person.Tom();

自动调用父类无参构造函数

class Person {
	String name = "";
	int age = 0;
}

class Student extends Person {
	String number = "";
}

var s = new Student();

显式调用父类构造函数

class Person {
	String name = "";
	int age = 0;
	
	Person(this.name, age);
	
	Person.myself(int age) {
		name = "Tom";
		this.age = age;
	}
}

class Student extends Person {
	String number = "";

	Student(String name, int age, String number): super(name, age) {
		this.number = number;
	}

	Student.myself(int age, String number): this.number = number, super.myself(age) {
	}
}

var s1 = new Student("Tom", 10, "no.1");
var s2 = new Student.myself(10);

成员方法/实例方法

class Person {
	String name = "";
	int age = 0;

	String info() {
		return "Person name is $name and age is $age.";
	}
}

var s = new Student();
s.info();

静态方法/类方法

class Person {
	String name = "";
	int age = 0;

	static readme() {
		print("Person!");
	}
}

Person.readme();

继承

不支持多继承。

class Person {
	String name = "";
	int age = 0;
	
	String info() {
		return "Person name is $name and age is $age.";
	}
}

class Student extends Person {
	String number = "";
}

var s = new Student();
s.info();

函数重写

class Person {
	String name = "";
	int age = 0;
	
	String info() {
		return "Person name is $name and age is $age.";
	}
}

class Student extends Person {
	String number = "";
	
	@override
	String info() {
		return super.info() + " Student number is $number.";
	}
}

运算符重写

class Person {
	String name = "";
	int age = 0;
	
	Person(this.name, this.age);
		
	Person operator +(Person p) {
		var name = this.name + " and " + p.name;
		var age = this.age + p.age;
		return new Person(name, age);
	}
}

var p1 = new Person("Tom", 10);
var p2 = new Person("Jerry", 9);
var p = p1 + p2;

可重写的运算符有：

• <
• <=

• =

• ==
• /
• ~/
• %
• &
• |
• ^
• ~
• <<
• []
• []=

抽象类与抽象方法

抽象类无法被实例化。

abstract class Person {
	String name = "";
	int age = 0;
	
	String info();
}

class Student extends Person {
	String number = "";
	
	@override
	String info() {
		return "Person name is $name and age is $age. Student number is $number.";
	}
}

接口

class Person {
	String name = "";
	int age = 0;
}

abstract class Say {
	int voice = 0;

	void say();
}

class Hello {
	void hello() {
		print("hello!");
	}
}

class Student extends Person implements Say, Hello {
	String number = "";

	@override
	int voice = 0;

	@override
	void say() {
		print("Person name is $name and age is $age. Student number is $number.");
	}

	@override
	void hello() {
		print("hello!");
		say();
	}
}

Mixin特性

class Person {
	String name = "";
	int age = 0;
}

class Run {
	void run() {
		print("run!");
	}
}

abstract class Say {
	void say();
}

class Student extends Person with Run implements Say {
	String number = "";

	@override
	void say() {
		print("Person name is $name and age is $age. Student number is $number.");
	}
}

var s = new Student();
s.run();

可调用的类

class Run {
	call() {
		print("run");
	}
}

class Say {
	call(String a, String b) {
		print("say $a $b");
	}
}

var run = new Run();
run();

var say = new Say();
say("a", "b");

枚举

无法继承，无法使用Mixin特性，无法实例化。

enum Grade {
	grade1,
	grade2
}

var grade = Grade.grade1;
var index = Grade.grade1.index;

类型定义

typedef Repeat = String Function(String str);
typedef Name = String;

Name name = "Tom";
Repeat f = (str) {
  return str + ", " + str;
};
var s = f(name);

泛型

函数泛型

String add<T>(T a, T b) {
	return a.toString() + b.toString();
}

String addString<T extends String>(T a, T b) {
	return a + b;
}

add(1, 2);
addString("a", "b");

类泛型

class Add<T> {
	String add(T a, T b) {
		return a.toString() + b.toString();
	}
}

class AddString<T extends String> {
	String add(T a, T b) {
		return a + b;
	}
}

new Add().add(1, 2);
new AddString().add("a", "b");

异步

异步本质上是使用isolates运行模式进行并发。

void main(List<String> args) {
	work();
	print(2);
}

work() async {
	print(1);
	var str = await takeTime();
	print(4);
	print(str);
}

Future<String> takeTime() async {
	var str = await new Future.delayed(new Duration(seconds: 2), () {
		print("...");
		print(3);
		return "hello";
	});
	return str;
}

在循环中异步

void main(List<String> args) async {
	Stream<String> stream = Stream.fromFuture(new Future.delayed(new Duration(seconds: 2), () {
		print("...");
		print(2);
		return "hello";
	}));
	print(1);
	await for (var str in stream) {
			print(str);
	}
	print(3);
}

注解/元数据

@deprecated

弃用。

@deprecated
// Should use Hello();
void hello() {
}

@override

重写。

class Person {
	String name = "";
}

class Student extends Person {
	@override
	String name = "";
}

@proxy

注释

单行注释

// Comment.

多行注释

/*
Comment.
Comment.
Comment.
*/

/* Comment.
Comment.
Comment. */

文档注释

/**
 * This is a demo.
 * 
 * Refer [say] for detail.
 */
void hello() {
}

/// This is a demo.
/// Used by [hello].
void say() {
}

库

标识符除非以“_”开头，否则都是对库外可见的。

import内置库

import 'dart:math';

void main(List<String> args) {
  print(pi);
}

import包库

import 'package:flutter/material.dart';

import本地库

lib.dart：

var _name = "lib.dart";

class Hello {
	void hello() {
		print("hello " + _name);
	}
}

main.dart：

import 'lib.dart';

void main(List<String> args) {
	new Hello().hello();
}

import-as

src/liba.dart：

class Hello {
	void helloA() {
		print("hello a");
	}
}

src/libb.dart：

class Hello {
	void helloB() {
		print("hello b");
	}
}

main.dart：

import 'src/liba.dart' as liba;
import 'src/libb.dart' as libb;

void main(List<String> args) {
	new liba.Hello().helloA();
	new libb.Hello().helloB();
}

import-show

lib.dart：

class Hello {
}

class Say {
}

class Run {
}

main.dart：

import 'lib.dart' show Hello, Say;

void main(List<String> args) {
	new Hello();
	new Say();
}

import-hide

lib.dart：

class Hello {
}

class Say {
}

class Run {
}

main.dart：

import 'lib.dart' hide Run;

void main(List<String> args) {
	new Hello();
	new Say();
}

import-deferred as懒加载

lib.dart：

class Hello {
	hello() {
		print("hello");
	}
}

main.dart：

import 'lib.dart' deferred as lib;

void main(List<String> args) {
	print("main");
	hello();
}

void hello() async {
	await lib.loadLibrary();
	new lib.Hello().hello();
}

包

包目录结构如下：

• lib/：源代码目录。
  • src/：私有源代码目录。
• pubspec.yaml：配置文件。

flutter包的material.dart：

export 'src/material/app.dart';

main.dart：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
	const MyApp({super.key});
	
	@override
	Widget build(BuildContext context) {
		return const MaterialApp(
			title: 'Flutter Demo'
		);
	}
}