ViewChildren 与 templateRef

Question

I want to use ViewChildren make QueryList from TemplateRef , but can't pass to input component.

For example

Component.ts:

@ViewChildren(TemplateRef) cellTemplates: QueryList<TemplateRef<any>>;

View:

<my-component [templatesRef]="cellTemplates"></my-component>

Input:

_templatesRef;
@Input()
set templatesRef(refs: any) {
   this._templatesRef = refs;
}

ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'ngIf: false'. Current value: 'ngIf: true'.

See in Stackbilitz

Answer 1

You should force parent to detect changes after getting the cellTemplates from template, so try to use ChangeDetectorRef in parent:

export class AppComponent  {
  name = 'Angular';
  @ViewChildren(TemplateRef, {read: TemplateRef}) cellTemplates: QueryList<TemplateRef<any>>;
  constructor(private cd: ChangeDetectorRef) { }
  ngOnInit(){ }
  ngAfterViewInit(){
    this.cd.detectChanges();
  }
}

You can find detailed explanations about that exception in this article .

DEMO

Answer 2

An ugly work around is, in your app-component

<my-component *ngIf="yet" [templatesRef]="cellTemplates"></my-component>

Implements afterViewInit and use a setTimeout

export class AppComponent implements AfterViewInit  {
  yet=false;

  ngAfterViewInit()
  {
    setTimeout(()=>{
      this.yet=true
    })
  }
}

The problem is that at first cellTemplates is a empty query and afterViewInit get elements,

Answer 3

Why not use the view variable you created instead?

<my-component [templatesRef]="title"></my-component>

<ng-template #title>
    ok
</ng-template>

Answer 4

Another solution without using ChangeDetectorRef & setTimeout .

@ViewChildren(TemplateRef, {read: TemplateRef})
set cellTemplates(refs: QueryList<TemplateRef<any>>) {
    this._cellTemplates = refs;
}