Configures a content query.

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Description

You can use ContentChild to get the first element or the directive matching the selector from the content DOM. If the content DOM changes, and a new child matches the selector, the property will be updated.

Content queries are set before the ngAfterContentInit callback is called.

Metadata Properties:

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

Options

Usage notes

Example

import {AfterContentInit, ContentChild, Directive} from '@angular/core';

@Directive({selector: 'child-directive'})
class ChildDirective {
}

@Directive({selector: 'someDir'})
class SomeDir implements AfterContentInit {
  @ContentChild(ChildDirective) contentChild !: ChildDirective;

  ngAfterContentInit() {
    // contentChild is set
  }
}

Example

import {Component, ContentChild, Directive, Input} from '@angular/core';

@Directive({selector: 'pane'})
export class Pane {
  // TODO(issue/24571): remove '!'.
  @Input() id !: string;
}

@Component({
  selector: 'tab',
  template: `
    <div>pane: {{pane?.id}}</div> 
  `
})
export class Tab {
  // TODO(issue/24571): remove '!'.
  @ContentChild(Pane) pane !: Pane;
}

@Component({
  selector: 'example-app',
  template: `
    <tab>
      <pane id="1" *ngIf="shouldShow"></pane>
      <pane id="2" *ngIf="!shouldShow"></pane>
    </tab>
    
    <button (click)="toggle()">Toggle</button>
  `,
})
export class ContentChildComp {
  shouldShow = true;

  toggle() { this.shouldShow = !this.shouldShow; }
}