关于oop:聊聊IOC中依赖注入那些事-dependency-inject

91次阅读

共计 6358 个字符，预计需要花费 16 分钟才能阅读完成。

What is Dependency injection

依赖注入定义为 组件之间依赖关系由容器在运行期决定，形象的说即由容器动静的将某个依赖关系注入到组件之中 在面向对象编程中，咱们常常解决的问题就是解耦，管制反转 (IoC) 就是罕用的面向对象编程的设计准则，其中依赖注入是管制反转最罕用的实现。指标解决以后类不负责被依赖类实例的创立和初始化。

what is Dependency

依赖是程序中常见的景象，假如有 A和 B 都被 C 耦合依赖着，在 OOP 编程中依赖无处不在。依赖模式有多种表现形式，比方一个类向另一个类发消息，一个类是另一个类的成员，一个类是另一个类的参数。

class A {}

class B {
  classA: A;
  constructor() {this.classA = new A();
  }
}

class C {
  classA: A;
  classB: B;
  constructor() {this.classA = new A();
    this.classB = new B();}
}

when is use Dependency injection

eg: 以用户调用 API 层打印日志来阐明

  • LoggerService被 ApiService 和UserService所依赖
  • ApiService被 UserService 所依赖
class LoggerService {constructor() { }
    log(args) {console.log(args)
    }
}

class ApiService {
    constructor (private readonly logger: LoggerService) {this.logger.log('api constructor')
    }

    public async getMydata () {return { name: 'mumiao', hobby: 'focusing in web'}
    }
}

class UserService {
    constructor (
        private readonly api: ApiService,
        private readonly logger: LoggerService
    ) {this.logger.log('user constructor')
    }

    async getMyhobby () {const { hobby} = await this.api.getMydata()
        return hobby
    }
}

async function Main {const loggerService = new LoggerService()
    const apiService = new ApiService(loggerService)
    const userService = new UserService(loggerService, userService)
    console.log('my hobby is', await userService.getMyhobby())
}

Main()
存在的问题
  • Unit tests 很难写
  • 组件不易复用和保护，可扩展性比拟低
  • UserService 不应该承载 ApiService 和LoggerService实例的创立。
如何解决

采纳依赖注入，UserService不负责被依赖类的创立和销毁，而是通过内部传入 api 和logger对象的形式注入。常见依赖注入形式有三种，本文次要以结构器注入为例解释。

const apiService = Injector.resolve < ApiService > ApiService;
const userService = Injector.resolve < UserService > UserService;
// returns an instance of , with all injected dependencies

implement simply Dependency injection

准备常识

  • ES6 的平时业务中绝对应用较少的个性：Reflect、Proxy、Decorator、Map、Symbol
  • 理解 Dependency injection，ES/TS 装璜器
  • 深刻了解 TypeScript – Reflect Metadata
Reflect
简介

Proxy 与 Reflect 是 ES6 为了操作对象引入的 API，Reflect 的 API 和 Proxy 的 API 一一对应，并且能够函数式的实现一些对象操作。另外，应用 reflect-metadata 能够让 Reflect 反对元编程

类型获取
  • 类型元数据：design:type
  • 参数类型元数据：design:paramtypes
  • 函数返回值类型元数据：design:returntype
Reflect.defineMetaData(metadataKey, metadataValue, target) // 在类上定义元数据
Reflect.getMetaData("design:type", target, propertyKey); // 返回类被装璜属性类型
Reflect.getMetaData("design:paramtypes", target, propertyKey); // 返回类被装璜参数类型
Reflect.getMetaData("design:returntype", target, propertyKey); // 返回类被装璜函数返回值类型
Decorators
function funcDecorator(target, name, descriptor) {
  // target 指 类的 prototype name 是函数名 descriptor 是属性描述符
  let originalMethod = descriptor.value;
  descriptor.value = function () {console.log("我是 Func 的装璜器逻辑");
    return originalMethod.apply(this, arguments);
  };
  return descriptor;
}

class Button {
  @funcDecorator
  onClick() {console.log("我是 Func 的原有逻辑");
  }
}
Reflect and Decorators
const Injector = (): ClassDecorator => {
  // es7 decorator
  return (target, key, descriptor) => {console.log(Reflect.getMetadata("design:paramtypes", target));
    // [apiService, loggerService]
  };
};

@Injector()
class userService {constructor(api: ApiService, logger: LoggerService) {}}
implement simply Dependency injection
// interface.ts

type Type<T = any> = new (...args: any[]) => T;
export type GenericClassDecorator<T> = (target: T) => void;

// ServiceDecorator.ts

const Service = (): GenericClassDecorator<Type<object>> => {return (target: Type<object>) => {};};

// Injector.ts
export const Injector = {
  // resolving instances
  resolve<T>(target: Type<any>): T {
    // resolved injections from the Injector
    let injections = Reflect.getMetadata("design:paramtypes", target) || [],
      injections = injections.map((inject) => Injector.resolve<any>(inject));

    return new target(...injections);
  },
};

只实现了依赖提取的外围局部，依赖注入还有一个局部是 Container 容器存储相干。

Resolve Dependency
@Service()
class LoggerService {//...}

@Service()
class ApiService {
    constructor (private readonly logger: LoggerService) {}}

@Service
class UserService {
    constructor (
        private readonly api: ApiService,
        private readonly logger: LoggerService
    ) {}}

async function Main {
    // jnject dependencies
   const apiService = Injector.resolve<ApiService>(ApiService);
   const userService = Injector.resolve<UserService>(UserService);
   console.log('my hobby is', await userService.getMyhobby())
}

Main()
implement simply Dependency injection with container

APIs of InversifyJS with TypeScript

应用步骤

  • Step 1: 申明接口及类型
  • Step 2: 申明依赖应用 @injectable & @inject decorators
  • Step 3: 创立并配置一个 Container
  • Step 4: 解析并提取依赖

示例

申明接口及类型：

export interface ILoggerService {}
export interface IApiService {}
export interface IUserService {}

export default TYPES = {
  // 惟一依赖标识，倡议应用 Symbol.for 替换类作为标识符
  ILoggerService: Symbol.for("ILoggerService"),
  IApiService: Symbol.for("IApiService"),
  IUserService: Symbol.for("IUserService"),
};

申明依赖：

import 'reflect-metadata'
import {injectable, inject} from 'inversify'

@injectable()
export class LoggerService implements ILoggerService{//...}

@injectable()
export class ApiService implements IApiService{
    protected _logger: LoggerService
    constructor (private @inject(TYPES.ILoggerService) logger: LoggerService
    ) {this._logger = logger}
}

也能够应用 property injection 代替 constructor injection，这样就不必申明构造函数。

@injectable()
export class ApiService implements IApiService {@inject(TYPES.ILoggerService) private _logger: LoggerService;
}
@injectable()
export class UserService implements IUserService {
    protected _api: ApiService;
    protected _logger: LoggerService;

    constructor (private readonly @inject(TYPES.IApiService) api: ApiService,
        private readonly @inject(TYPES.ILoggerService) logger: LoggerService
    ) {
        this._api = api
        this._logger = logger
    }
}

创立并配置一个 Container

...
const DIContainer = new container()
DIContainer.bind<ApiService>(TYPES.IApiService).toSelf()
DIContainer.bind<LoggerService>(TYPES.ILoggerService).toSelf()

解析依赖

import "reflect-matadata";
import {UserService} from "./services";
import DIContainer from "./container";

async function Main() {
  const userService: UserService = DIContainer.resolve<UserService>(UserService);
  console.log("my hobby is", await userService.getMyhobby());
}

Main();
Classes as identifiers and circular dependencies

An exception:

Error: Missing required @Inject or @multiinject annotation in: argument 0 in class Dom.

import "reflect-metadata";
import {injectable} from "inversify";

@injectable()
class Dom {
  public _domUi: DomUi;
  constructor(@inject(DomUi) domUi: DomUi) {this._domUi = domUi;}
}

@injectable()
class DomUi {
  public _dom;
  constructor(@inject(Dom) dom: Dom) {this._dom = dom;}
}

@injectable()
class Test {
  public _dom;
  constructor(@inject(Dom) dom: Dom) {this._dom = dom;}
}

container.bind<Dom>(Dom).toSelf();
container.bind<DomUi>(DomUi).toSelf();
const dom = container.resolve(Test); // Error!

次要起因：decorator 被调用时，类还没有申明，导致inject(undefined)，InversifyJS 举荐应用 Symboy.for 生成依赖惟一标识符

inject practice frameWorks

依赖注入个别都借助第三方框架来实现，实现须要思考循环依赖，错误处理，容器存储等。

  • tsyringe：https://github.com/microsoft/tsyringe
    实际：https://github.com/DTStack/molecule
  • InversifyJS: https://github.com/inversify/InversifyJS
    实际：https://codesandbox.io/s/github/inversify/inversify-express-example/tree/master/?file=/BindingDecorators/controller/user.ts

作者信息

正文完
oop
发表至： oop
2021-05-14
 0
关于oop:对面向对象的进一步认识
关于抽象工厂模式:抽象工厂模式
关于oop:聊聊IOC中依赖注入那些事-dependency-inject
关于设计模式:简单工厂模式