Angular

What it does

Configures a content query.

How to use

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

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

@Directive({selector: 'someDir'})
class SomeDir implements AfterContentInit {
  @ContentChildren(ChildDirective) contentChildren: QueryList<ChildDirective>;

  ngAfterContentInit() {
    // contentChildren is set
  }
}

Description

You can use ContentChildren to get the QueryList of elements or directives from the content DOM. Any time a child element is added, removed, or moved, the query list will be updated, and the changes observable of the query list will emit a new value.

Content queries are set before the ngAfterContentInit callback is called.

Metadata Properties:

selector - the directive type or the name used for querying.
descendants - include only direct children or all descendants.
read - read a different token from the queried elements.

Let's look at an example:

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

@Directive({selector: 'pane'})
export class Pane {
  @Input() id: string;
}

@Component({
  selector: 'tab',
  template: `
    <div>panes: {{serializedPanes}}</div> 
  `
})
export class Tab {
  @ContentChildren(Pane) panes: QueryList<Pane>;

  get serializedPanes(): string { return this.panes ? this.panes.map(p => p.id).join(', ') : ''; }
}

@Component({
  selector: 'example-app',
  template: `
    <tab>
      <pane id="1"></pane>
      <pane id="2"></pane>
      <pane id="3" *ngIf="shouldShow"></pane>
    </tab>

    <button (click)="show()">Show 3</button>
  `,
})
export class ContentChildrenComp {
  shouldShow = false;

  show() { this.shouldShow = true; }
}

npm package: @angular/core

exported from @angular/core/index defined in @angular/core/src/metadata/di.ts