Angular：如何在父組件中注入具體類

Question

我有一個通用組件

@Component({
  selector: 'mc-common',
  ...
})
CommonComponent {

 constructor(@Optional() @SkipSelf() private readonly mergingStrategy: MergingStrategy) {
    if (!this.mergingStrategy) {
      this.mergingStrategy = new NoopMergingStrategy();
    }
 }
 ...
}

另一個使用mc-common組件

@Component({
  selector: 'mc-another',
  template: `
     <mc-commo>
      ...
     </mc-common>
  `,
  providers: [{
    provide: MergingStrategy, useClass: ComplicatedMergingStrategy // or useValue: new ComplicatedMergingStrategy()
  }
})
AnotherComponent {

 constructor(private readonly mergingStrategy: MergingStrategy) {

 }
 ...
}

因此，當我調用mc-another ， mc-common會將ComplicatedMergingStrategy作為MergingStrategy實例。

一切都像這樣正常工作。 但是我想要實現的是將ComplicatedMerginStrategy的相同實例注入AnotherComponent而不是抽象，而是繼續在mc-common使用抽象。

就像是：

AnotherComponent {

 constructor(private readonly mergingStrategy: ComplicatedMergingStrategy) {

 }
 ...
}

策略：

abstract class MergingStrategy {
  merge(a, b): any
}

class NoopMergingStrategy implements MergingStrategy {
   merge(a, b): any {
    return a;
   }
}

class ComplicatedMergingStrategy implements MergingStrategy {
   merge(a, b) {
    ...
   }
}

我希望我很清楚:)

Answer 1

解決方法是useExisting並在之前聲明ComplicatedMerginStrategy的實例。

@Component({
  selector: 'mc-another',
  template: `
     <mc-commo>
      ...
     </mc-common>
  `,
  providers: [
    ComplicatedMerginStrategy, {
    provide: MerginStrategy, useExisting: ComplicatedMerginStrategy
  }]
})
AnotherComponent {

 constructor(private readonly merginStrategy: ComplicatedMerginStrategy) {

 }
 ...
}