将服务从主项目注入到创建的库中

Question

我使用Angular 8。

此问题仅适用于Angular DI专家。

起初，我制作了一个Angular库，该库将在许多项目中重复使用。

在这个库中，我提供了一个抽象服务，必须在项目中使用它来定义。

我在我的库中定义了一个名为BridgeService的抽象类

并且在我的主项目中，我创建实现它的BridgeService ：（在下一行中，我将向您展示抽象的BridgeService）

MainProject> BridgeService：

import { BridgeService as AbstractBridgeService } from 'myLibrary';

@Injectable()
export class BridgeService implements AbstractBridgeService {

    hello(){
        alert('hello Word');
    }
}

MainProject> UsersModule：

import { UsersModule as LibraryUsersModule } from 'myLibrary';

@NgModule({
    imports: [
        CommonModule,
        LibraryUsersModule,
    ],
    //...
    providers: [
        BridgeService
        // some try:
        //{ provide: BridgeService, useClass: BridgeService }
    ],
})
export class UsersModule {

    constructor(private bridgeService: BridgeService){
        this.bridgeService.hello();
    }

}

现在我们必须查看与库有关的文件：

Library> bridge.service.ts：

export abstract class BridgeService {
    abstract hello(): void;
}

此BridgeService必须在UsersModule中定义

Library> UsersModule：

@NgModule({
    //...
    providers: [
        // My Try:
        { provide: BridgeService, useValue: BridgeService} 
    ],
})
export class UsersModule {

    # my goal is that I can uncomment this piece of code:

    //constructor(private bridgeService: BridgeService){
    //  this.bridgeService.hello();
    //}

}

我希望您仅触摸此代码中的两行：

1）在库的UsersModule提供程序数组中：我要声明为通用的BridgeService行。

2）在项目的UsersModule提供程序数组中：我想定义的BridgeService行代替Library UserModule中的摘要。

Answer 1

仅需在库中定义一个令牌即可。在您的库中，定义令牌和接口：

/** Token to inject the bridge service */
export const BRIDGE_SERVICE_ADAPTER:
    InjectionToken<BridgeServiceAdapter> =
        new InjectionToken<BridgeServiceAdapter>('Bridge service token');

export interface BridgeServiceAdapter {
  hello(): void;
}

在您的库中，您可以像这样注入它：

export class UsersModule {
  constructor(
    @Inject(BRIDGE_SERVICE_ADAPTER) private bridgeService: BridgeServiceAdapter
  ){
    this.bridgeService.hello();
  }
}

而且，在您要使用库的应用程序中：

import { BridgeServiceAdapter } from 'myLibrary';

@Injectable({providedIn: 'root'})
export class BridgeService implements BridgeServiceAdapter {
    hello() { alert('hello Word') }
}

...
import { UsersModule as LibraryUsersModule, BRIDGE_SERVICE_ADAPTER } from 'myLibrary';

@NgModule({
    imports: [CommonModule,LibraryUsersModule,...],
    providers: [{ provide: BRIDGE_SERVICE_ADAPTER, useExisting: BridgeService }],
})
export class UsersModule {
  // Obs 1: ok, this seems something you should be encapsulating inside
  //   your library to doesn't have to inject in the dependent projects
  // Obs 2: and, here, in the app, as I created BridgeService decorated
  //   with {providedIn: 'root'}, I can inject the service itself. But
  //   if this wasn't the case, I'd have to inject it using the same notation
  //   used in the library: 
  //   @Inject(BRIDGE_SERVICE_ADAPTER) private bridgeService: BridgeServiceAdapter
  //   This would be necessary if, I had provided my service like:
  //   { provide: BRIDGE_SERVICE_ADAPTER, useClass: BridgeService }
  //   on the above line, notice "useClass" instead of "useExisting"
  constructor(private bridgeService: BridgeService) {
    this.bridgeService.hello();
  }
}