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ViewChild

属性装饰器,用于配置一个视图查询。 变更检测器会在视图的 DOM 中查找能匹配上该选择器的第一个元素或指令。 如果视图的 DOM 发生了变化,出现了匹配该选择器的新的子节点,该属性就会被更新。

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.

查看"说明"...

说明

在调用 NgAfterViewInit 回调函数之前就会设置这些视图查询。

View queries are set before the ngAfterViewInit callback is called.

元数据属性

Metadata Properties:

  • selector - 用于查询的指令类型或名字。

    selector - the directive type or the name used for querying.

  • read - 从查询到的元素中读取另一个令牌。

    read - read a different token from the queried elements.

所支持的选择器包括:

Supported selectors include:

  • 任何带有 @Component@Directive 装饰器的类

    any class with the @Component or @Directive decorator

  • 字符串形式的模板引用变量(比如可以使用 @ViewChild('cmp') 来查询 <my-component #cmp></my-component>

    a template reference variable as a string (e.g. query <my-component #cmp></my-component> with @ViewChild('cmp'))

  • 组件树中任何当前组件的子组件所定义的提供商(比如 @ViewChild(SomeService) someService: SomeService

    any provider defined in the child component tree of the current component (e.g. @ViewChild(SomeService) someService: SomeService)

  • 任何通过字符串令牌定义的提供商(比如 @ViewChild('someToken') someTokenVal: any

    any provider defined through a string token (e.g. @ViewChild('someToken') someTokenVal: any)

  • TemplateRef(比如可以用 @ViewChild(TemplateRef) template; 来查询 <ng-template></ng-template>

    a TemplateRef (e.g. query <ng-template></ng-template> with @ViewChild(TemplateRef) template;)

选项

使用说明

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. }

例子

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. }

例子

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. }