I know I can just pass the template reference variable mytemplate to *ngTemplateOutlet and it works.

For learning purposes I want to use different approach via @ViewChild decorator. However I got some errors that I don't understand.

Minimal Code:

import { Component, TemplateRef, ViewChild } from '@angular/core';

@Component({
  selector: 'app-root',
  template:
    `
<ng-template #mytemplate>
<p>Hello World</p>
</ng-template>
<ng-container *ngTemplateOutlet="template"></ng-container>
`
})
export class AppComponent {
  @ViewChild("mytemplate")
  template!: TemplateRef<any>;
}

Error Messages:

core.mjs:7640 ERROR Error: NG0100: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'undefined'. Current value: '[object Object]'. Find more at https://angular.io/errors/NG0100
    at throwErrorIfNoChangesMode (core.mjs:8207:11)
    at bindingUpdated (core.mjs:14552:17)
    at Module.ɵɵproperty (core.mjs:15284:9)
    at AppComponent_Template (app.component.ts:10:16)
    at executeTemplate (core.mjs:12121:9)
    at refreshView (core.mjs:11984:13)
    at refreshComponent (core.mjs:13080:13)
    at refreshChildComponents (core.mjs:11774:9)
    at refreshView (core.mjs:12034:13)
    at renderComponentOrTemplate (core.mjs:12101:9)

CodePudding user response：

1. This is the error which comes only in dev mode

2. But still this should not be there in console.

3. You can manually trigger change detection to avoid this issue

    constructor(private cd: ChangeDetectorRef) {}
   
    ngAfterViewChecked(){
        this.cd.detectChanges()
    }
   

Link to documnetation : https://angular.io/errors/NG0100