Flutter 开发Tips （第一期）

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延展操作符(...)可以对数组或者字典进行操作

// 合并数组
test1() {
  var list = [1, 2, 3];
  var list2 = [0, ...list, 4];
  print(list2);
  // [0, 1, 2, 3, 4]
}

// 合并字典
test2() {
  var map1 = {
    "key1": "value1",
    "key2": "value2",
  };
  var map2 = {
    "key3": "value3",
    "key4": "value4",
  };
  var map3 = {...map1, ...map2};
  print(map3);
  // {key1: value1, key2: value2, key3: value3, key4: value4}
}

for ()…[]

合并widgets到集合中，使用for ()...[]范式，使用延展操作符(...)来合并一个数组的widgets到一个存在的集合中。例如在构造Row或者Column的children时，非常方便。下面是示例：

List<Food> foods = [
  Food(name: 'apple', isVegetarian: true),
  Food(name: 'nuts', isVegetarian: true),
  Food(name: 'eggs', isVegetarian: true),
  Food(name: 'chicken', isVegetarian: false),
];

class Food {
  Food({
    this.name,
    this.isVegetarian,
  });

  String name;
  bool isVegetarian;
}

class HomePage extends StatelessWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [
          Container(),
          for (final food in foods) ...[
            if (food.isVegetarian) ListTile(title: Text(food.name)),
            SizedBox(height: 50.0),
          ],
        ],
      ),
    );
  }

() {} ()

立即执行一个匿名函数：() {} (),相当于声明一个匿名函数并且里面执行，这种范式在处理一个widget可能有多种输出时特别有用。而不是使用镶嵌的三目运算符或者通过一个函数调用，这个代码跟内联。下面是示例：

T getRandomElement<T>(List<T> list) => list[Random().nextInt(list.length)];

Column(
          children: [
            Container(
              color: () {
                switch (getRandomElement(foods).name) {
                  case 'apple':
                    return Colors.green;
                  case 'nuts':
                    return Colors.brown;
                  case 'eggs':
                    return Colors.yellow;
                  default:
                    return Colors.transparent;
                }
              }(),
              child: Text('Food of the Day'),
            ),
          ],
        )

代码静态分析

在提交代码时为了提高代码质量，保持团队的代码风格一致，需要进行代码静态分析，一般通过下面2种方法来进行

flutter analyze

使用flutter analyze进行代码静态分析,此命令会根据analysis_options.yaml定义的规则进行静态分析

dartfmt

使用dartfmt ./ -w对当前目录以及子目录的dart代码进行代码,-w选项会自动重写文件使其符合规范。

使用dartfmt ./ -n显示当前目录以及子目录的dart代码格式可以修改的文件但是不做修改，可以配合ci分析代码格式问题。

更多选项请使用dartfmt --help查看

Push & present & Pop

// Push by route
Navigator.pushNamed(context, '/b')
  
// push 
Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) => MyPage()));

// present
Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) => MyPage(),fullscreenDialog: true));

// pop
Navigator.pop(context)
  
// pop + push
Navigator.of(context)
	..pop()
	..pop()
	..pushNamed('/settings');

API

// push
Future push(BuildContext context, Route route)

// pop
bool pop(BuildContext context, [ result ])
  
// 下面两种是等效的
Navigator.push(BuildContext context, Route route)
Navigator.of(context).push(Route route)

1
2
3

final RenderBox box = keyContext.findRenderObject();
final size = box.size;
final topLeftPosition = box.localToGlobal(Offset.zero);

Model To JSON

json_serializable

引入

dependencies:
  # Your other regular dependencies here
  json_annotation: ^2.0.0

dev_dependencies:
  # Your other dev_dependencies here
  build_runner: ^1.0.0
  json_serializable: ^2.0.0

使用

import 'package:json_annotation/json_annotation.dart';

// user.g.dart 将在我们运行生成命令后自动生成
part 'user.g.dart';

///这个标注是告诉生成器，这个类是需要生成Model类的
@JsonSerializable()

class User{
  User(this.name, this.email);

  String name;
  String email;
  //不同的类使用不同的mixin即可
  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
  Map<String, dynamic> toJson() => _$UserToJson(this);
}

单次解析：flutter packages pub run build_runner build
持续集成：flutter packages pub run build_runner watch
json_serializable 在线json转dart model工具

Built value

在线json转build value 模板工具 https://charafau.github.io/json2builtvalue/
VSCode built value 插件

Sample code

// interface model
import 'package:built_value/built_value.dart';

part 'user.g.dart';

abstract class User implements Built<User, UserBuilder> {
  String get name;
  @nullable
  String get nickname;
  User._();
  factory User([updates(UserBuilder b)]) = _$User;
}

// init
var user1 = new User((b) => b
    ..name = 'John Smith'
    ..nickname = 'Joe');

// update
var user2 = user.rebuild((b) => b
    ..nickname = 'Jojo');

// update
var updatedStructuredData = structuredData.rebuild((b) => b
    ..user.update((b) => b
        ..name = 'Johnathan Smith')
    ..credentials.phone.update((b) => b
        ..country = Country.switzerland
        ..number = '555 01234 555'));


// nested builders
abstract class Node implements Built<Node, NodeBuilder> {
  @nullable
  String get label;
  @nullable
  Node get left; 
  @nullable
  Node get right;
  Node._();
  factory Node([updates(NodeBuilder b)]) = _$Node;
}

// new or update
var node = new Node((b) => b
  ..left.left.left.right.left.right.label = 'I’m a leaf!'
  ..left.left.right.right.label = 'I’m also a leaf!');
var updatedNode = node.rebuild((b) => b
  ..left.left.right.right.label = 'I’m not a leaf any more!'
  ..left.left.right.right.right.label = 'I’m the leaf now!');

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