Angular: how to make NgControl react to valueChanges only of the host <input>

问题

I am using a directive on an <input>-element and get a reference to its controls like this:

@ContentChild(NgControl) private readonly _inputNgControl: NgControl;

But when I listen to model-changes like so:

  ngAfterContentInit(): void {
    this._inputNgControl.control.valueChanges
      .distinctUntilChanged()
      .subscribe(value => {
         // ...
    });
  }

it appears that this._inputNgControl.control refers not to the input that the directive is sitting on, but to ALL inputs in my parent component (which contains multiple <input>-elements with the same directive) because I get changes from all of those inputs in the parent and not only the one where I typed something.

So how can I filter the valueChange's of only the active input? Do I need to use the constructor to inject it, will that make the NgControl local instead of global? Or do I need to implement VALUE_ACCESSOR myself with forwardRef (which is what NgControl is doing as far as I understand it)?

The least clean solution would be passing an id to the directive and make

.filter(() => this._directiveId === this._inputNgControl.name)

so I want to avoid that if possible.

回答1:

What helped was to use HostListener. I have been using HostListener so far only to handle native browser events, like listening to keyboard actions or mouse scrolling, but I had no idea you can use them to get access to the outputs of the host element (thus the name host listener, duh!) as well:

@HostListener('ngModelChange', ['$event'])
onModelChange(value: string | number) { this.modelChange$.next(value); }

And then in the component with the ContentChild:

@Component({
  selector: input-wrapper',
  template: `<ng-content></ng-content>`
})
export class InputWrapperComponent implements AfterContentInit {
  @ContentChild(InputControllerDirective) private _icd: InputControllerDirective;

  ngAfterContentInit() {
    this._icd.modelChange$.subscribe((value: string | number) => {
       // do sth.
    })
  }
}

来源：https://stackoverflow.com/questions/50724559/angular-how-to-make-ngcontrol-react-to-valuechanges-only-of-the-host-input