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目录

依赖模块

// Importing core libraries
import 'dart:math';

// Importing libraries from external packages
import 'package:lib1/lib1.dart';
import 'package:lib2/lib2.dart' as lib2;

// Only dart compile js supports deferred loading
import 'package:greetings/hello.dart' deferred as hello;

// Import only foo.
import 'package:lib1/lib1.dart' show foo;
// Import all names EXCEPT foo.
import 'package:lib2/lib2.dart' hide foo;

// Importing files
import 'path/to/my_other_file.dart';

变量与常量

var foo = Bar();            // 默认
var foo = Bar(args);        // 构造
var foo = initializer;      // 拷贝
var foo = other as Bar;     // 转换
var [a, b] = list;          // 解构
var {'a': a, 'b': b} = map; // 解构
var (a, b: b, :c) = record; // 解构

final map = {if (i is int) i: 'int'};         // final 不可改变变量本身，但可以改变其字段内容
const set = {if (list is List<int>) ...list}; // const 两者都不可改变
enum Color { red, green, blue }               // 支持定义拥有字段的枚举

语句

  • 分支

    // if else
if (condition) {
  statement;
} else {
  statement;
}

// switch
switch (comparable) {
  case constant1:
    continue fallthrough;
  fallthrough:
  case constant2:
    statement;
    break;
  default:
    statement;
}

  • 循环

    // for
for (declaration; condition; expression) {
  statement;
}

// for in
for (final elem in iterabal) {
  statement;
}

  • 异常

    try {
  breedMoreLlamas();
} on OutOfLlamasException {
  // A specific exception
  buyMoreLlamas();
} on Exception catch (e) {
  // Anything else that is an exception
  print('Unknown exception: $e');
} catch (e) {
  // No specified type, handles all
  print('Something really unknown: $e');
} catch (e, s) {
  print('Exception details:\n $e');
  print('Stack trace:\n $s');
  rethrow;
} finally {
  // Always clean up, even if an exception is thrown.
  cleanLlamaStalls();
}

函数

String fn({required String r1, required String? r2, String o1 = "optional", String? o2}) {...}

String fn(String r1, String? r2 [String o1 = "optional", String? o2]) {...}

(arg) {return ...}

(arg) => expression;

面向对象

封装

class MyClass {
  String _name;

  // constructor likes function but no return type
  MyClass(String name) {
    this._name = name;
  }

  // named constructor beacase no funtion overload
  MyClass.named(String name) {
    this._name = name;
  }

  // using this in constructor, a syntax sugar
  MyClass.useThis(this._name);

  // initializer lists: final fields must have values before the constructor body executes
  MyClass.initList(String name) : _name = name;

  // redirect to another constructor
  MyClass.redirecting1(String name) : this(name);
  MyClass.redirecting2(String name) : this.named(name);

  @override
  bool operator ==(Object other) => other is MyClass && other._name = name;

  String get name => name;
  set name(String value) => name = value;
}

继承

class Base {
  int key;
  void baseMethod() {
    // ...
  }
}

mixin Mixin {
  void mixinMethod() {
    // ...
  }
}

class MyClass extends Base with Mixin {
  MyClass(super.key);

  @override
  void baseMethod() {
    super.baseMethod();
    // ...
  }
}

多态

abstract class Abstract {
  void abstractMethod();
}

class MyClass implements Abstract {
  @override
  void abstractMethod() {
    // ...
  }
}

内置类型

var b = true && false;

var i = 10 + 0xFF;

var d = 1.1 + 1.1e5;

var s = 'with " ' + "with ' " + "with ${name}" + r"with raw without any \e and $name";
var s1 = '''
You can create
multi-line strings like this one.
''';
var s2 = """This is also a
multi-line string.""";

vat list0 = <String>[]
var list1 = [1, 2, 3];
var list2 = [0, ...list1];
var list3 = [0, ...?list1];
var list4 = ['Home', 'Plants', if (promoActive) 'Outlet'];
var list5 = ['#0', for (var i in list1) '#$i'];

var set0 = <String>{};
var set1 = {1, 2, 3};
var set2 = {0, ...set1};
var set3 = {0, ...?set1};
var set4 = {'Home', 'Plants', if (promoActive) 'Outlet'};
var set5 = {'#0', for (var i in set1) '#$i'};

var map0 = <int, String>{};
var map1 = {1: 'one', 2: 'two', 3: 'three'};
var map2 = {0: 'zero', ...map1};
var map3 = {0: 'zero', ...?map1};
var map4 = {'Home', 'Plants', if (promoActive) 'Outlet'};
var map5 = {'#0', for (var i in map1.entries) i.key: i.value};

var record = ("ape", a: "bat", "cat", b: "dog");
print(record.$1); // Prints "ape".
print(record.a);  // Prints "bat".
print(record.$2); // Prints "cat".
print(record.b);  // Prints "dog".
var number = (123);  // The number 123.
var record = (123,); // A record containing the number 123.
var (bool, num id, {int n, String s}) quad;
var t = (int, String); // No record type literals