NG0200: Circular dependency in DI detected，为什么并且我该怎么做？

Question

我想往子组件中注入父组件，但是有一个错误：

Error: NG0200: Circular dependency in DI detected for ParentComponent

子组件：

@Component({
  selector: 'cy-parent',
  templateUrl: './parent.component.html',
  styleUrls: ['./parent.component.scss'],
  providers: [
    {provide: ParentComponent, useExisting: forwardRef(() => ParentComponent)}
  ]
})

export class ParentComponent {
  constructor() { }
}

父组件：

@Component({
  selector: 'cy-child',
  templateUrl: './child.component.html',
  styleUrls: ['./child.component.scss'],

})
export class ChildComponent implements OnInit {
  constructor(
    @SkipSelf() @Optional() public _parentComp?: ParentComponent
  ) {
   
   }
}