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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 或 @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.     
  15.     <button (click)="toggle()">Toggle</button>
  16.        
  17.     <div>Selected: {{selectedPane}}</div> 
  18.   `,
  19. })
  20. export class ViewChildComp {
  21.   @ViewChild(Pane)
  22.   set pane(v: Pane) {
  23.     setTimeout(() => { this.selectedPane = v.id; }, 0);
  24.   }
  25.   selectedPane: string = '';
  26.   shouldShow = true;
  27.   toggle() { this.shouldShow = !this.shouldShow; }
  28. }

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.     
  15.     <button (click)="toggle()">Toggle</button>
  16.        
  17.     <div>Selected: {{selectedPane}}</div> 
  18.   `,
  19. })
  20. export class ViewChildComp {
  21.   @ViewChild(Pane)
  22.   set pane(v: Pane) {
  23.     setTimeout(() => { this.selectedPane = v.id; }, 0);
  24.   }
  25.   selectedPane: string = '';
  26.   shouldShow = true;
  27.   toggle() { this.shouldShow = !this.shouldShow; }
  28. }