[Angular] ViewChild 'read' option

It is not clear in the Docs about {read: xx} option for @ViewChild.

Based on the Source code, @ViewChild as view as Component, ElementRef, TemplateRef.

For example, we have:

<one></one>

  @ViewChild(OneComponent)
  one: OneComponent;

  ngAfterViewInit() {
    console.log('after', this.one);
  }

Now we read 'OneComponent' as a component, if we want to read it as ElementRef, we can do:

  @ViewChild(OneComponent, {read: ElementRef})
  one: ElementRef;

[NOTICE]:

One thing to notice is that @ViewChild is only for viewing the its own component tamplate, you cannot view its child component template or parent component template