Can you get the component encapsulation host ID?

2020-03-27 17:11发布

问题:

Is there a way to get the encapsulation host id that is given to a component?

If you have a component that is using ViewEncapsulation.Emulated the element in the DOM will have an attribute name of something like _nghost-par-2. Which, is a unique ID given to the component to encapsulate the associated styles.

How do you get that ID as part of the component's constructor?

Something to the effect of:

@Component({
  hostId:string;
  ...
})
export class myComponent implements OnInit {
  constructor(host:Host) {
    this.hostId = host.id;
  }
  ...
}

回答1:

This ID consists of the following parts:

_nghost   -   par    -     2
   |           |           |
 static      APP_ID   _nextCompTypeId

APP_ID is a just token from @angular/core

If you need to avoid randomly generated value to be used as an application id, you can provide a custom value via a DI provider configuring the root Injector using this token

_nextCompTypeId is generated inside framework within private class ViewUtils.

Seems there is no a public method which can return it value. So probably the following will work

export class MyComponent { 
  id: string;
  constructor(@Inject(APP_ID) appId: string, vcRef: ViewContainerRef) {
    this.id = `${appId}-${vcRef.injector['_view'].viewUtils._nextCompTypeId - 1}`;
  }
}

Another way is get it from attributes via elementRef