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ViewChild

Property decorator that configures a view query. The change detector looks for the first element or the directive matching the selector in the view DOM. If the view DOM changes, and a new child matches the selector, the property is updated.

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Description

View queries are set before the ngAfterViewInit callback is called.

Metadata Properties:

  • selector - the directive type or the name used for querying.
  • read - read a different token from the queried elements.

Supported selectors include:

  • any class with the @Component or @Directive decorator
  • a template reference variable as a string (e.g. query <my-component #cmp></my-component> with @ViewChild('cmp'))
  • any provider defined in the child component tree of the current component (e.g. @ViewChild(SomeService) someService: SomeService)
  • any provider defined through a string token (e.g. @ViewChild('someToken') someTokenVal: any)
  • a TemplateRef (e.g. query <ng-template></ng-template> with @ViewChild(TemplateRef) template;)

Options

Usage notes

import {Component, Directive, Input, ViewChild} from '@angular/core'; @Directive({selector: 'pane'}) export class Pane { // TODO(issue/24571): remove '!'. @Input() id !: string; } @Component({ selector: 'example-app', template: ` <pane id="1" *ngIf="shouldShow"></pane> <pane id="2" *ngIf="!shouldShow"></pane> <button (click)="toggle()">Toggle</button> <div>Selected: {{selectedPane}}</div> `, }) export class ViewChildComp { @ViewChild(Pane) set pane(v: Pane) { setTimeout(() => { this.selectedPane = v.id; }, 0); } selectedPane: string = ''; shouldShow = true; toggle() { this.shouldShow = !this.shouldShow; } }
      
      
  1. import {Component, Directive, Input, ViewChild} from '@angular/core';
  2.  
  3. @Directive({selector: 'pane'})
  4. export class Pane {
  5. // TODO(issue/24571): remove '!'.
  6. @Input() id !: string;
  7. }
  8.  
  9. @Component({
  10. selector: 'example-app',
  11. template: `
  12. <pane id="1" *ngIf="shouldShow"></pane>
  13. <pane id="2" *ngIf="!shouldShow"></pane>
  14. <button (click)="toggle()">Toggle</button>
  15. <div>Selected: {{selectedPane}}</div>
  16. `,
  17. })
  18. export class ViewChildComp {
  19. @ViewChild(Pane)
  20. set pane(v: Pane) {
  21. setTimeout(() => { this.selectedPane = v.id; }, 0);
  22. }
  23. selectedPane: string = '';
  24. shouldShow = true;
  25. toggle() { this.shouldShow = !this.shouldShow; }
  26. }

Example

import {AfterViewInit, Component, Directive, ViewChild} from '@angular/core'; @Directive({selector: 'child-directive'}) class ChildDirective { } @Component({selector: 'someCmp', templateUrl: 'someCmp.html'}) class SomeCmp implements AfterViewInit { // TODO(issue/24571): remove '!'. @ViewChild(ChildDirective) child !: ChildDirective; ngAfterViewInit() { // child is set } }
      
      
  1. import {AfterViewInit, Component, Directive, ViewChild} from '@angular/core';
  2.  
  3. @Directive({selector: 'child-directive'})
  4. class ChildDirective {
  5. }
  6.  
  7. @Component({selector: 'someCmp', templateUrl: 'someCmp.html'})
  8. class SomeCmp implements AfterViewInit {
  9. // TODO(issue/24571): remove '!'.
  10. @ViewChild(ChildDirective) child !: ChildDirective;
  11.  
  12. ngAfterViewInit() {
  13. // child is set
  14. }
  15. }

Example

import {Component, Directive, Input, ViewChild} from '@angular/core'; @Directive({selector: 'pane'}) export class Pane { // TODO(issue/24571): remove '!'. @Input() id !: string; } @Component({ selector: 'example-app', template: ` <pane id="1" *ngIf="shouldShow"></pane> <pane id="2" *ngIf="!shouldShow"></pane> <button (click)="toggle()">Toggle</button> <div>Selected: {{selectedPane}}</div> `, }) export class ViewChildComp { @ViewChild(Pane) set pane(v: Pane) { setTimeout(() => { this.selectedPane = v.id; }, 0); } selectedPane: string = ''; shouldShow = true; toggle() { this.shouldShow = !this.shouldShow; } }
      
      
  1. import {Component, Directive, Input, ViewChild} from '@angular/core';
  2.  
  3. @Directive({selector: 'pane'})
  4. export class Pane {
  5. // TODO(issue/24571): remove '!'.
  6. @Input() id !: string;
  7. }
  8.  
  9. @Component({
  10. selector: 'example-app',
  11. template: `
  12. <pane id="1" *ngIf="shouldShow"></pane>
  13. <pane id="2" *ngIf="!shouldShow"></pane>
  14. <button (click)="toggle()">Toggle</button>
  15. <div>Selected: {{selectedPane}}</div>
  16. `,
  17. })
  18. export class ViewChildComp {
  19. @ViewChild(Pane)
  20. set pane(v: Pane) {
  21. setTimeout(() => { this.selectedPane = v.id; }, 0);
  22. }
  23. selectedPane: string = '';
  24. shouldShow = true;
  25. toggle() { this.shouldShow = !this.shouldShow; }
  26. }