Can a structural directive refer to a child component using @ContentChild?

问题

If I have a custom directive ParentDirective and custom component ChildComponent arranged like so:

<div appParent>
  <app-child></app-child>
</div>

...then I can use @ContentChild in the directive to refer to the component:

@ContentChild(ChildComponent) child: ChildComponent;

See this StackBlitz where this is working. (It logs to the console to show that the child member is set).

However, if I change appParent into a structural directive, then the child member is never set.

<div *appParent>
  <app-child></app-child>
</div>

See this StackBlitz.

Is it not possible to use @ContentChild with structural directives?

回答1:

I think you cannot, and that is due to the design used by angular for both type of directives. Creating a directive via TemplateRef and injecting it via createEmbeddedView of ViewContainerRef generates the template as a sibling in the dom, not as a child. Therefore, Angular's injection also respects this so the child and the place of creation cannot see each other. You can draw it in your mind as an extra added layer there.

Here is the source code of the createEmbeddedView

  createEmbeddedView(context: any): EmbeddedViewRef<any> {
    return new ViewRef_(Services.createEmbeddedView(
        this._parentView, this._def, this._def.element !.template !, context));
  }

As you can see, it returns a new ViewRef where it injects your context.

More details here.

来源：https://stackoverflow.com/questions/53560347/can-a-structural-directive-refer-to-a-child-component-using-contentchild