ViewChild 在角度 13 中未定义

Question

我试图从父组件调用子组件的视图子组件，但在控制台中未定义。

查看图像还可以看到相同的堆栈火焰

https://stackblitz.com/edit/angular-ivy-k4m2hp?file=src%2Fapp%2Fhello.component.ts

import { Component, Input, OnInit, ViewChild } from '@angular/core';
import { TestChildComponent } from './test-child/test-child.component';

@Component({
  selector: 'hello',
  template: `<h1>this is Hello component {{name}}!</h1>`,
  styles: [`h1 { font-family: Lato; }`],
})
export class HelloComponent {
  @Input() name: string;
@ViewChild('TestChildComponent') testChildComponent: TestChildComponent
  ngOnInit() {
    console.log('calling ngOninit in hello component');
    console.log('going to call test child instance this.TestChildComponent.ngOninit')
   console.log(this.testChildComponent);
  }
}

请帮忙获取子组件

this.testChildComponent

这样我就可以从父级调用子级的 ngOnInit 。

this.testChildComponent.ngOnInit()

Answer 1

如果你设置 viewChild { static: true } 你将能够在 ngOnInit 中访问它

但在您的示例中，问题是由于 testChildComponent 是 app.component 而不是 hello.component 的子级

<app-test-child childname="{{ name }}" #test></app-test-child>

应用程序组件.ts

import { Component, VERSION, ViewChild } from '@angular/core';
import { TestChildComponent } from './test-child/test-child.component';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
})
export class AppComponent {
  name = 'this is from app compoenent';
  @ViewChild('test', { static: true }) testChildComponent: TestChildComponent;

  ngOnInit() {
    console.log('calling ngOninit in app component');
    console.log(this.testChildComponent);
  }
}

如果您想从 hello.component 访问 testChildComponent，您必须将组件作为示例的输入发送给它

以下是访问 testChildComponent 的工作示例

https://stackblitz.com/edit/angular-ivy-tvwukg?file=src%2Fapp%2Fapp.component.html