001.5 flutter之dart最佳实践

Effective Dart: Usage

• DO use strings in part of directives.
  尽管part语法会导致一个库的源码被分散到多个文件中（一个库就一个文档多好哇），但dart官网还是推荐使用part的（这样主文件更能突显该库的核心功能，非核心功能放到别的文件嘛）,因此对于下述两种写法，优选good：

library my_library;
part "some/other/file.dart";

// good
part of "../../my_library.dart";

// bad
part of my_library;

• DON’T import libraries that are inside the src directory of another package.
  尽管可以，但尽量不要引用别人库的src中的代码

• 在自己的库中引用自己的文件，dart官网推荐使用相对路径

my_package
└─ lib
   ├─ src
   │  └─ utils.dart
   └─ api.dart
// good
import 'src/utils.dart';

// bad
import 'package:my_package/src/utils.dart';

Booleans 布尔

• DO use ?? to convert null to a boolean value.
  当一个表达式的结果有true, false, or null三种值，但只能使用true, false的时候（比如if语句的条件表达式不接受null，会抛异常的），强烈推荐使用??将null转为true或者false

// good
// If you want null to be false:
optionalThing?.isEnabled ?? false;

// If you want null to be true:
optionalThing?.isEnabled ?? true;

// easy like this
if (optionalThing?.isEnabled??true) {
  print("Have enabled thing.");
}

// ----------------------------------------
// bad
// If you want null to be false:
optionalThing?.isEnabled == true;//对于这种写法，别人很可能以为==true是冗余的，可以删除，但实际上是不可以的

// If you want null to be true:
optionalThing?.isEnabled != false;

Strings 字符串

• DO use adjacent strings to concatenate string literals.

// good（不推荐用在第一行字符串后写一个冗余的+加号）
raiseAlarm(
    'ERROR: Parts of the spaceship are on fire. Other '
    'parts are overrun by martians. Unclear which are which.');

• PREFER using interpolation to compose strings and values.（不要老想着用+加号去连接字符串）

// good
'Hello, $name! You are ${year - birth} years old.';

• AVOID using curly braces in interpolation when not needed.

// 类似$name，name两边不要加冗余的小括号
'Hi, $name!'
    "Wear your wildest $decade's outfit."
    'Wear your wildest ${decade}s outfit.'

Collections

• DO use collection literals when possible.

var points = [];// 不推荐 var points = List();
var addresses = {};// 不推荐 var addresses = Map();
var points = [];// 不推荐 var points = List();
var addresses = {};// 不推荐 var addresses = Map();

• DON’T use .length to see if a collection is empty.

// 判断空不空，建议这样写，尽量避免.length，效率painfully slow
if (lunchBox.isEmpty) return 'so hungry...';
if (words.isNotEmpty) return words.join(' ');

• CONSIDER using higher-order methods to transform a sequence.

// 推荐这种写法，避免for循环
var aquaticNames = animals
    .where((animal) => animal.isAquatic)
    .map((animal) => animal.name);

• AVOID using Iterable.forEach() with a function literal.

// js中经常用Iterable.forEach() ，但dart官网推荐用for
for (var person in people) {
  ...
}

• DON’T use List.from() unless you intend to change the type of the result.

// good
var iterable = [1, 2, 3];// Creates a List:
print(iterable.toList().runtimeType);// Prints "List":
var numbers = [1, 2.3, 4]; // List.
numbers.removeAt(1); // Now it only contains integers.
var ints = List.from(numbers);// change the type of the result

// ----------------------------------------
// bad
var iterable = [1, 2, 3];// Creates a List:
print(List.from(iterable).runtimeType);// Prints "List":

• DO use whereType() to filter a collection by type.

// good
var objects = [1, "a", 2, "b", 3];
var ints = objects.whereType();

// ----------------------------------------
// bad
var objects = [1, "a", 2, "b", 3];
var ints = objects.where((e) => e is int);//it returns an Iterable