# Dart代码编写规则

# 文件名命名规范

文件及文件夹名称采用下划线命名法，例：

my_widget/
├── empty_list.dart
├── form_widgets.dart
├── handwritten_signature.dart
├── installed_car_card.dart
├── launch_card.dart
├── loading_more.dart
├── loading_spinner.dart
├── my_button.dart
├── my_dialog.dart
├── my_picker.dart
├── recent_car_card.dart
├── search_bar.dart
├── show_document.dart
├── upgrade_dialog.dart
└── upload_images.dart

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# 代码编写规则-引入pedantic (opens new window)

友情提示

此规则不包含格式化规则，请手动格式化代码

在pubspec.yaml中引入pedantic，放在dev_dependencies下面

dev_dependencies:
  pedantic: ^1.9.0

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在项目根目录新建文件analysis_options.yaml，内容：

# 导入pedantic规则
include: package:pedantic/analysis_options.yaml

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保存，完成

# 代码编写规则-详细规则说明

提示

以下中文大部分为机器翻译，仅供参考
最好直接看代码，比较清晰

always_declare_return_types

官方解释及翻译

declare method return types.
声明方法的返回类型

错误示例❌

main() { }

_bar() => _Foo();

class _Foo {
  _foo() => 42;
}

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正确示例✅

void main() { }

_Foo _bar() => _Foo();

class _Foo {
  int _foo() => 42;
}

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always_require_non_null_named_parameters

官方解释及翻译

specify @required on named parameters without a default value on which an assert(param != null) is done.
如果参数加了非空断言，则此参数是必传的@required或者此参数有一个非空默认值

错误示例❌
```
void m1({a}) {
  assert(a != null);
}
```
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正确示例✅
```
void m1({@required a}) {
  assert(a != null);
}

void m2({a: 1}) {
  assert(a != null);
}
```
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annotate_overrides

官方解释及翻译

annotate overridden methods and fields.
重写方法必须加@override注解

错误示例❌

class Cat {
  int get lives => 9;
}

class Lucky extends Cat {
  final int lives = 14;
}

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正确示例✅

abstract class Dog {
  String get breed;
  void bark() {}
}

class Husky extends Dog {

  @override
  final String breed = 'Husky';

  @override
  void bark() {}
}

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avoid_empty_else

官方解释及翻译

AVOID empty else statements.
避免空的else语句

错误示例❌
```
if (x > y)
  print("1");
else ;
print("2");
```
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正确示例✅
```
if (x > y)
  print("1");
else
  print("2");
```
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avoid_init_to_null

官方解释及翻译

Don't explicitly initialize variables to null.
不要将变量显式初始化为null

错误示例❌

int _nextId = null;

class LazyId {
  int _id = null;

  int get id {
    if (_nextId == null) _nextId = 0;
    if (_id == null) _id = _nextId++;

    return _id;
  }
}

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正确示例✅

int _nextId;

class LazyId {
  int _id;

  int get id {
    if (_nextId == null) _nextId = 0;
    if (_id == null) _id = _nextId++;

    return _id;
  }
}

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avoid_null_checks_in_equality_operators

官方解释及翻译

DON'T check for null in custom == operators.
不要在自定义==运算符中检查null

错误示例❌

class Person {
  final String name;

  @override
  operator == (other) =>
      other != null && other is Person && name == other.name;
}

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正确示例✅

class Person {
  final String name;

  @override
  operator == (other) => other is Person && name == other.name;
}

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avoid_relative_lib_imports

官方解释及翻译

DO avoid relative imports for files in lib/.
避免使用相对路径导入文件

错误示例❌
```
import 'package:foo/bar.dart';

import '../lib/baz.dart';
```
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正确示例✅
```
import 'package:foo/bar.dart';

import 'baz.dart';
```
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avoid_return_types_on_setters

官方解释及翻译

AVOID return types on setters.
避免在set方法上声明返回类型

错误示例❌
```
void set speed(int ms);
```
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正确示例✅
```
set speed(int ms);
```
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avoid_shadowing_type_parameters

官方解释及翻译

AVOID shadowing type parameters.
避免隐蔽类型参数

错误示例❌
```
class A<T> {
  void fn<T>() {}
}
```
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正确示例✅
```
class A<T> {
  void fn<U>() {}
}
```
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avoid_types_as_parameter_names

官方解释及翻译

AVOID using a parameter name that is the same as an existing type.
避免使用与现有类型相同的参数名

错误示例❌
```
m(f(int));
```
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正确示例✅
```
m(f(int v));
```
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camel_case_extensions

官方解释及翻译

DO name extensions using UpperCamelCase.
extensions命名规范采用帕斯卡命名法

正确示例✅
```
extension MyFancyList<T> on List<T> { 
  // ... 
}

extension SmartIterable<T> on Iterable<T> {
  // ...
}
```
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curly_braces_in_flow_control_structures

官方解释及翻译

DO use curly braces for all flow control structures.
所有逻辑控制语句都要使用花括号

错误示例❌

if (overflowChars != other.overflowChars)
  return overflowChars < other.overflowChars;

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正确示例✅

if (overflowChars != other.overflowChars) {
  return overflowChars < other.overflowChars;
}

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empty_catches

官方解释及翻译

AVOID empty catch blocks.
避免空的catch块

错误示例❌
```
try {
  dio.get();
} catch(exception) { }
```
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正确示例✅
```
try {
  dio.get();
} catch(e) {
  doSomething(e);
}
```
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empty_constructor_bodies

官方解释及翻译

DO use ; instead of {} for empty constructor bodies.
使用分号代替空构造方法块的花括号

错误示例❌
```
class Point {
  int x, y;
  Point(this.x, this.y) {}
}
```
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正确示例✅
```
class Point {
  int x, y;
  Point(this.x, this.y);
}
```
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library_names

官方解释及翻译

DO name libraries using lowercase_with_underscores.
library命名规范采用下划线命名法

错误示例❌
```
library peg-parser;
```
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正确示例✅
```
library peg_parser;
```
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library_prefixes

官方解释及翻译

DO use lowercase_with_underscores when specifying a library prefix.
指定库前缀时，请使用下划线命名法

错误示例❌

import 'dart:math' as Math;
import 'dart:json' as JSON;
import 'package:js/js.dart' as JS;
import 'package:javascript_utils/javascript_utils.dart' as jsUtils;

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正确示例✅

import 'dart:math' as math;
import 'dart:json' as json;
import 'package:js/js.dart' as js;
import 'package:javascript_utils/javascript_utils.dart' as js_utils;

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no_duplicate_case_values

官方解释及翻译

DON'T use more than one case with same value.
switch case中请勿添加多个相同的值

错误示例❌
```
const int A = 1;
switch (v) {
  case 1:
  case 2:
  case A:
  case 2:
}
```
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正确示例✅
```
const int A = 1;
switch (v) {
  case A:
  case 2:
}
```
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null_closures

官方解释及翻译

DO NOT pass null as an argument where a closure is expected.
不要在期望关闭的地方传递null作为参数

错误示例❌
```
[1, 3, 5].firstWhere((e) => e.isOdd, orElse: null);
```
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正确示例✅
```
[1, 3, 5].firstWhere((e) => e.isOdd, orElse: () => null);
```
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omit_local_variable_types

官方解释及翻译

CONSIDER omitting type annotations for local variables.
考虑忽略局部变量的类型注释

错误示例❌

Map<int, List<Person>> groupByZip(Iterable<Person> people) {
  Map<int, List<Person>> peopleByZip = <int, List<Person>>{};
  for (Person person in people) {
    peopleByZip.putIfAbsent(person.zip, () => <Person>[]);
    peopleByZip[person.zip].add(person);
  }
  return peopleByZip;
}

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正确示例✅

Map<int, List<Person>> groupByZip(Iterable<Person> people) {
  var peopleByZip = <int, List<Person>>{};
  for (var person in people) {
    peopleByZip.putIfAbsent(person.zip, () => <Person>[]);
    peopleByZip[person.zip].add(person);
  }
  return peopleByZip;
}

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prefer_adjacent_string_concatenation

官方解释及翻译

DO use adjacent strings to concatenate string literals.
使用相邻的字符串来连接字符串文字

错误示例❌

raiseAlarm(
'ERROR: Parts of the spaceship are on fire. Other ' +
'parts are overrun by martians. Unclear which are which.');

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正确示例✅

raiseAlarm(
'ERROR: Parts of the spaceship are on fire. Other '
'parts are overrun by martians. Unclear which are which.');

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prefer_collection_literals

官方解释及翻译

DO use collection literals when possible.
尽可能使用集合文字

错误示例❌

var points = new List();
var addresses = new Map();
var uniqueNames = new Set();
var ids = new LinkedHashSet();
var coordinates = new LinkedHashMap();

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正确示例✅

var points = [];
var addresses = <String,String>{};
var uniqueNames = <String>{};
var ids = <int>{};
var coordinates = <int,int>{};

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prefer_conditional_assignment

官方解释及翻译

PREFER using ??= over testing for null.
使用??=判空并赋值

错误示例❌

String get fullName {
  if (_fullName == null) {
    _fullName = getFullUserName(this);
  }
  return _fullName;
}

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正确示例✅

String get fullName {
  return _fullName ??= getFullUserName(this);
}

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prefer_contains

官方解释及翻译

DON'T use indexOf to see if a collection contains an element.
不要使用indexOf来判断集合是否包含某个元素

错误示例❌
```
if (lunchBox.indexOf('sandwich') == -1 return 'so hungry...';
```
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正确示例✅
```
if (!lunchBox.contains('sandwich') return 'so hungry...';
```
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prefer_equal_for_default_values

官方解释及翻译

DO Use = to separate a named parameter from its default value.
使用=给参数设置默认值

错误示例❌
```
m({a: 1})
```
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正确示例✅
```
m({a = 1})
```
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prefer_final_fields

官方解释及翻译

DO prefer declaring private fields as final if they are not reassigned later in the class.
如果不稍后在类中重新分配私有字段，请不要将私有字段声明为final

错误示例❌

class BadImmutable {
  var _label = 'hola mundo! BadImmutable'; // LINT
  var label = 'hola mundo! BadImmutable'; // OK
}

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正确示例✅

class GoodImmutable {
  final label = 'hola mundo! BadImmutable', bla = 5; // OK
  final _label = 'hola mundo! BadImmutable', _bla = 5; // OK
}

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prefer_for_elements_to_map_fromIterable

官方解释及翻译

When building maps from iterables, it is preferable to use for elements.
从可迭代对象构建map时，最好用于元素

错误示例❌

Map<String, WidgetBuilder>.fromIterable(
  kAllGalleryDemos,
  key: (demo) => '${demo.routeName}',
  value: (demo) => demo.buildRoute,
);

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正确示例✅

return {
  for (var demo in kAllGalleryDemos) {
    '${demo.routeName}': demo.buildRoute,
  }
};

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prefer_generic_function_type_aliases

官方解释及翻译

PREFER generic function type aliases.
优选通用函数类型别名

错误示例❌
```
typedef void F();
```
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正确示例✅
```
typedef F = void Function();
```
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prefer_if_null_operators

官方解释及翻译

Prefer using if null operators instead of null checks in conditional expressions.
最好在条件表达式中使用??运算符而不是空检查

错误示例❌
```
v = a == null ? b : a;
```
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正确示例✅
```
v = a ?? b;
```
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prefer_is_empty

官方解释及翻译

DON'T use length to see if a collection is empty.
不要使用length属性来查看集合是否为空

错误示例❌

if (lunchBox.length == 0) return 'so hungry...';
if (words.length != 0) return words.join(' ');

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正确示例✅

if (lunchBox.isEmpty) return 'so hungry...';
if (words.isNotEmpty) return words.join(' ');

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prefer_is_not_empty

官方解释及翻译

PREFER x.isNotEmpty to !x.isEmpty for Iterable and Map instances.
对于Iterable和Map实例，直接只用isNotEmpty判断其长度不是0

错误示例❌
```
if (!sources.isEmpty) {
  process(sources);
}
```
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正确示例✅
```
if (todo.isNotEmpty) {
  sendResults(request, todo.isEmpty);
}
```
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prefer_iterable_whereType

官方解释

PREFER iterable.whereType<T>() over iterable.where((e) => e is T).

错误示例❌
```
iterable.where((e) => e is MyClass)
```
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正确示例✅
```
iterable.whereType<MyClass>()
```
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prefer_single_quotes

官方解释及翻译

DO use single quotes where they wouldn't require additional escapes.
除非字符串内部还有引号，否则字符串最外部的引号都使用单引号

错误示例❌

useStrings(
  "should be single quote",
  r"should be single quote",
  r"""should be single quotes""")

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正确示例✅

useStrings(
  'should be single quote',
  r'should be single quote',
  r'''should be single quotes''',
  "here's ok",
  "nested ${a ? 'strings' : 'can'} be wrapped by a double quote",
  'and nested ${a ? "strings" : "can be double quoted themselves"}');

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prefer_spread_collections

官方解释及翻译

Use spread collections when possible.
尽可能使用spread方式合并集合

错误示例❌

Widget build(BuildContext context) {
  return CupertinoPageScaffold(
    child: ListView(
      children: [
        Tab2Header(),
      ]..addAll(buildTab2Conversation()),
    ),
  );
}

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正确示例✅

Widget build(BuildContext context) {
  return CupertinoPageScaffold(
    child: ListView(
      children: [
        Tab2Header(),
        ...buildTab2Conversation(),
      ],
    ),
  );
}

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recursive_getters

官方解释及翻译

DON'T create recursive getters.
不要创建递归的get方法

错误示例❌
```
int get field => field;
```
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正确示例✅
```
int get field => _field;
```
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slash_for_doc_comments

官方解释及翻译

PREFER using /// for doc comments.
使用///作为文档注释的首选项

正确示例✅

/// Parses a set of option strings. For each option:
///
/// * If it is `null`, then it is ignored.
/// * If it is a string, then [validate] is called on it.
/// * If it is any other type, it is *not* validated.
void parse(List options) {
  // ...
}

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type_init_formals

官方解释及翻译

DON'T type annotate initializing formals.
不要键入注释形式化形式

错误示例❌
```
class Point {
  int x, y;
  Point(int this.x, int this.y);
}
```
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正确示例✅
```
class Point {
  int x, y;
  Point(this.x, this.y);
}
```
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unawaited_futures

官方解释

DO await functions that return a Future inside of an async function body.

错误示例❌

void main() async {
  doSomething(); // Likely a bug.
}

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正确示例✅

Future doSomething() => ...;

void main() async {
  await doSomething();

  unawaited(doSomething()); // Explicitly-ignored fire-and-forget.
}

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unnecessary_const

官方解释及翻译

AVOID repeating const keyword in a const context.
在const上下文中避免重复使用const关键字

错误示例❌

class A { const A(); }
void m() {
  const a = const A();
  final b = const [const A()];
}

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正确示例✅

class A { const A(); }
void m() {
  const a = A();
  final b = const [A()];
}

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unnecessary_new

官方解释及翻译

AVOID new keyword to create instances.
新建实例省略new关键字

错误示例❌
```
class A { A(); }
void m() {
  final a = new A();
}
```
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正确示例✅
```
class A { A(); }
void m() {
  final a = A();
}
```
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unnecessary_null_in_if_null_operators

官方解释及翻译

AVOID using null as an operand in if null operators.
如果为null运算符，则避免使用null作为操作数

错误示例❌
```
var x = a ?? null;
var y = null ?? 1;
```
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正确示例✅
```
var x = a ?? 1;
```
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unnecessary_this

官方解释及翻译

DON'T use this when not needed to avoid shadowing.
不需要时请省略this

错误示例❌

class Box {
  var value;
  void update(new_value) {
    this.value = new_value;
  }
}

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正确示例✅

class Box {
  var value;
  void update(new_value) {
    value = new_value;
  }
}

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unrelated_type_equality_checks

官方解释及翻译

DON'T Compare references of unrelated types for equality.
请勿比较无关类型的引用是否相等

错误示例❌

void someFunction() {
  var x = '1';
  if (x == 1) print('someFunction'); // LINT
}

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正确示例✅

void someFunction() {
  var x = '1';
  if (x == '1') print('someFunction'); // LINT
}

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use_function_type_syntax_for_parameters

官方解释及翻译

Use generic function type syntax for parameters.
对参数使用通用函数类型语法

错误示例❌
```
Iterable<T> where(bool predicate(T element)) {}
```
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正确示例✅
```
Iterable<T> where(bool Function(T) predicate) {}
```
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use_rethrow_when_possible

官方解释及翻译

DO use rethrow to rethrow a caught exception.
请使用rethrow重新抛出捕获的异常

错误示例❌

try {
  somethingRisky();
} catch(e) {
  if (!canHandle(e)) throw e;
  handle(e);
}

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正确示例✅

try {
  somethingRisky();
} catch(e) {
  if (!canHandle(e)) rethrow;
  handle(e);
}

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valid_regexps

官方解释及翻译

DO use valid regular expression syntax when creating regular expression instances.
创建正则表达式实例时，请使用有效的正则表达式语法

错误示例❌
```
print(RegExp('(').hasMatch('foo()'));
```
1
正确示例✅
```
print(RegExp('[(]').hasMatch('foo()'));
```
1

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