本文更新於2024-12-22，使用Dart 2.18.2。

可以使用dart run FILENAME運行程序文件。

關鍵字

• 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聲明的是編譯時常量。

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();

變量

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

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

基本數據類型

數值

• int: 64位。範圍為[-2^63 ~ 2^{63-1]。編譯為JavaScript時使用JavaScript的範圍[-2}53 ~ 2^53-1]。
• double：64位。範圍約為[-1.7E308 ~ 1.7E308]。

字符串

使用UTF-16編碼。

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}";

布爾

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"
};

運算符

運算符優先級

從高到低依次為：

算數運算符

關係運算符

類型判定運算符

賦值運算符

邏輯運算符

位運算符

條件運算符

訪問運算符

流程控制

條件語句

if-else

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

switch-case

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

循環語句

for

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

for-in

for (var v in set) {
}

while

while (condition) {
}

do-while

do {
} while(condition);

break語句

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

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

continue語句

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

斷言

斷言只在開發（Checked）模式下有效，在生產（Production）模式下無效。

assert(flag);

異常

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

函數

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();

箭頭函數

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

可選位置參數

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

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

可選命名參數

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

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

閉包

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

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

主函數

void main(List<String> args) {
}

類

成員變量/實例變量

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

getter和setter

會為每個成員變量自動生成getter方法，對於非final修飾的成員變量也會自動生成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);

靜態變量/類變量

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

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

print(Person.total);

構造函數

構造函數的執行順序為：實例變量賦值 -> 初始化參數列表 -> 父類構造函數 -> 本類構造函數。

默認無參構造函數

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

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

默認自動生成無參構造函數：

	Person() {
	}

顯式聲明構造函數

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

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

命名構造函數

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

var p = new Person.myself(10);

構造函數簡寫

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);

重定向構造函數

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);

常量構造函數

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);

工廠方法的構造函數

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();

自動調用父類無參構造函數

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

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

var s = new Student();

顯式調用父類構造函數

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);

成員方法/實例方法

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

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

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

靜態方法/類方法

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

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

Person.readme();

繼承

不支持多繼承。

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();

函數重寫

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.";
	}
}

運算符重寫

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;

可重寫的運算符有：

• <
• <=

• =

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

抽象類與抽象方法

抽象類無法被實例化。

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();

可調用的類

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");

枚舉

無法繼承，無法使用Mixin特性，無法實例化。

enum Grade {
	grade1,
	grade2
}

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

類型定義

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

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

泛型

函數泛型

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");

類泛型

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");

異步

異步本質上是使用isolates運行模式進行併發。

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;
}

在循環中異步

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);
}

註解/元數據

@deprecated

棄用。

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

@override

重寫。

class Person {
	String name = "";
}

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

@proxy

註釋

單行註釋

// Comment.

多行註釋

/*
Comment.
Comment.
Comment.
*/

/* Comment.
Comment.
Comment. */

文檔註釋

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

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

庫

標識符除非以“_”開頭，否則都是對庫外可見的。

import內置庫

import 'dart:math';

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

import包庫

import 'package:flutter/material.dart';

import本地庫

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懶加載

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

包目錄結構如下：

• lib/：源代碼目錄。
  • src/：私有源代碼目錄。
• 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'
		);
	}
}