ContentChildren

Property decorator that configures a content query.

Use 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.

Does not retrieve elements or directives that are in other components' templates, since a component's template is always a black box to its ancestors.

Metadata Properties:

• selector - The directive type or the name used for querying.
• descendants - If true include all descendants of the element. If false then only query direct children of the element.
• emitDistinctChangesOnly - The QueryList#changes observable will emit new values only if the QueryList result has changed. When false the changes observable might emit even if the QueryList has not changed. ** Note: *** This config option is deprecated, it will be permanently set to true and removed in future versions of Angular.
• read - Used to read a different token from the queried elements.

The following selectors are supported.

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

In addition, multiple string selectors can be separated with a comma (e.g. @ContentChildren('cmp1,cmp2'))

The following values are supported by read:

• Any class with the @Component or @Directive decorator
• Any provider defined on the injector of the component that is matched by the selector of this query
• Any provider defined through a string token (e.g. {provide: 'token', useValue: 'val'})
• TemplateRef, ElementRef, and ViewContainerRef

Here is a simple demonstration of how the ContentChildren decorator can be used.

import {AfterContentInit, ContentChildren, Directive, QueryList} from '@angular/core';@Directive({ selector: 'child-directive', standalone: false,})class ChildDirective {}@Directive({ selector: 'someDir', standalone: false,})class SomeDir implements AfterContentInit { @ContentChildren(ChildDirective) contentChildren!: QueryList<ChildDirective>; ngAfterContentInit() { // contentChildren is set }}

Tab-pane example

Here is a slightly more realistic example that shows how ContentChildren decorators can be used to implement a tab pane component.

import {Component, ContentChildren, Directive, input, QueryList, signal} from '@angular/core';@Directive({ selector: 'pane', standalone: false,})export class Pane { id = input.required<string>();}@Component({ selector: 'tab', template: ` <div class="top-level">Top level panes: {{ serializedPanes }}</div> <div class="nested">Arbitrary nested panes: {{ serializedNestedPanes }}</div> `, standalone: false,})export class Tab { @ContentChildren(Pane) topLevelPanes!: QueryList<Pane>; @ContentChildren(Pane, {descendants: true}) arbitraryNestedPanes!: QueryList<Pane>; get serializedPanes(): string { return this.topLevelPanes ? this.topLevelPanes.map((p) => p.id()).join(', ') : ''; } get serializedNestedPanes(): string { return this.arbitraryNestedPanes ? this.arbitraryNestedPanes.map((p) => p.id()).join(', ') : ''; }}@Component({ selector: 'example-app', template: ` <tab> <pane id="1"></pane> <pane id="2"></pane> @if(shouldShow()) { <pane id="3"> <tab> <pane id="3_1"></pane> <pane id="3_2"></pane> </tab> </pane> } </tab> <button (click)="show()">Show 3</button> `, standalone: false,})export class ContentChildrenComp { shouldShow = signal(false); show() { this.shouldShow.set(true); }}