angular 2 access ng-content within component

问题:

How can I access the "content" of a component from within the component class itself?

I would like to do something like this:

<upper>my text to transform to upper case</upper>

How can I get the content or the upper tag within my component like I would use @Input for attributes?

@Component({
    selector: 'upper',
    template: `<ng-content></ng-content>`
})
export class UpperComponent {
    @Input 
    content: String;
}

PS: I know I could use pipes for the upper case transformation, this is only an example, I don't want to create an upper component, just know how to access the component's content from with the component class.

回答1:

You need to leverage the @ContentChild decorator for this.

@Component({
  selector: 'upper',
  template: `<ng-content></ng-content>`
})
export class UpperComponent {
  @Input 
  content: String;

  @ContentChild(...)
  element: any;
}

Edit

I investigated a bit more your issue and it's not possible to use @ContentChild here since you don't have a root inner DOM element.

You need to leverage the DOM directly. Here is a working solution:

@Component({
  selector: 'upper',
  template: `<ng-content></ng-content>`
})
export class UpperComponent {
  constructor(private elt:ElementRef, private renderer:Renderer) {
  }

  ngAfterViewInit() {
    var textNode = this.elt.nativeElement.childNodes[0];
    var textInput = textNode.nodeValue;
    this.renderer.setText(textNode, textInput.toUpperCase());
  }
}

See this plunkr for more details: https://plnkr.co/edit/KBxWOnyvLovboGWDGfat?p=preview

回答2:

If you want to get a reference to a component of the transcluded content, you can use:

@Component({
    selector: 'upper',
    template: `<ng-content></ng-content>`
})
export class UpperComponent {
    @ContentChild(SomeComponent) content: SomeComponent;
}

If you wrap <ng-content> then you can access access to the transcluded content like

@Component({
    selector: 'upper',
    template: `
  <div #contentWrapper>
    <ng-content></ng-content>
  </div>`
})
export class UpperComponent {
    @ViewChild('contentWrapper') content: ElementRef;

    ngAfterViewInit() {
      console.debug(this.content.nativeElement);
    }
}

回答3:

https://angular.io/api/core/ContentChildren

class SomeDir implements AfterContentInit {

  @ContentChildren(ChildDirective) contentChildren : QueryList<ChildDirective>;

  ngAfterContentInit() {
    // contentChildren is set
  }
}

Note that if you do console.log(contentChildren), it will only work on ngAfterContentInit or a later event.