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javascript - 无法将依赖注入派生类

问题描述

我有一个相对简单的设置，包含三个类。我正在使用inversify依赖注入。但是当将类MessageBroker注入派生类时Repository，它MessageBroker是未定义的：

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

const container = new Container();

const registerProviders = (...providers: any[]) =>
  providers.forEach(provider => container.bind(provider.name).to(provider));

const getProvider = (provider): any => container.get(provider.name);

@injectable()
export class MessageBroker {
  start = () => console.log('init message broker');
}

@injectable()
export abstract class Repository {
  @inject(MessageBroker.name) private mb: MessageBroker;

  constructor(@unmanaged() protected readonly user: any) {}

  // this.mb is undefined
  initialize = () => this.mb.start();
}

@injectable()
export class UserRepository extends Repository {
  constructor() {
    super({ user: 'some object' });
    this.initialize();
  }
}

registerProviders(UserRepository, Repository, MessageBroker);

const repo: UserRepository = getProvider(UserRepository);

你可以自己试试。我创建了一个小型 GitHub 存储库：https ://github.com/flulude/stackoverflow-inversify-injected-service-undefined

运行脚本时，我收到此错误：

/project/index.ts:22
  initialize = () => this.mb.start();
                             ^
TypeError: Cannot read property 'start' of undefined
    at UserRepository.Repository.initialize (/project/index.ts:22:30)
    at new UserRepository (/project/index.ts:29:10)
    at _createInstance (/project/node_modules/inversify/lib/resolution/instantiation.js:21:12)
    at Object.resolveInstance (/project/node_modules/inversify/lib/resolution/instantiation.js:41:18)
    at /project/node_modules/inversify/lib/resolution/resolver.js:72:42
    at Object.resolve (/project/node_modules/inversify/lib/resolution/resolver.js:96:12)
    at /project/node_modules/inversify/lib/container/container.js:319:37
    at Container._get (/project/node_modules/inversify/lib/container/container.js:310:44)
    at Container.get (/project/node_modules/inversify/lib/container/container.js:230:21)
    at getProvider (/project/index.ts:9:50)

PS 在将代码编译为 Javascript 时，我得到了几乎相同的错误

标签： javascripttypescriptdependency-injectioninversifyjsreflect-metadata

解决方案

您的 MessageBroker 仅设置在内存中，但从未被实例化，这就是它如何获得未定义的错误。在您的构造函数中，您需要设置

this.mb = new MessageBroker();

无需上述行即可执行此操作的另一种方法是将空参数签名构造函数添加到 MessageBroker 类中。

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