dart.md · mrbeardad/SeeCheatSheets

# 目录

- [目录](#目录)
  - [依赖模块](#依赖模块)
  - [变量与常量](#变量与常量)
  - [语句](#语句)
  - [函数](#函数)
  - [面向对象](#面向对象)
    - [封装](#封装)
    - [继承](#继承)
    - [多态](#多态)
  - [内置类型](#内置类型)

## 依赖模块

```dart
// 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

```dart
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

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

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

- 循环

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

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

- 异常

```dart
  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

```dart

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

```dart
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

```dart
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

```dart
abstract class Abstract {
  void abstractMethod();
}

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

## 内置类型

```dart
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 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
```

mrbeardad/SeeCheatSheets

简介

发行版

贡献者

近期动态

mrbeardad/SeeCheatSheets .gitee-modal { width: 500px !important; }

简介

发行版

贡献者

近期动态

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mrbeardad/SeeCheatSheets