ViewContainerRef 在 ngAfterViewInit 中调用时未定义

本文介绍了ViewContainerRef 在 ngAfterViewInit 中调用时未定义的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

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我想在初始化父组件时动态创建子组件，但是当我尝试在 ngAgterViewInit() 中创建它时，它抛出 ViewContainerRef 未定义的错误.

component.ts

 @ViewChild('container', {read: ViewContainerRef}) 容器:ViewContainerRef;构造函数(私有解析器:ComponentFactoryResolver){}ngAfterViewInit(){const factory = this.resolver.resolveComponentFactory(ChildComponent);this.container.createComponent(工厂);//此处未定义容器}

component.html

<预><代码>...<div class="row" #container ></div>...

解决方案

由于 div 在 ngIf 条件块内，它可能在 中不可用ngAfterViewInit.您可以通过使用 ViewChildren 和 QueryList.changes 事件监视元素的存在来保护代码免受这种可能性的影响:

@ViewChildren('container', { read: ViewContainerRef }) 容器:QueryList;ngAfterViewInit() {如果(this.containers.length > 0){//容器已经存在this.addComponent();};this.containers.changes.subscribe(() => {//容器已经添加到 DOMthis.addComponent();});}私人添加组件(){const 容器 = this.containers.first;const factory = this.resolver.resolveComponentFactory(ChildComponent);container.createComponent(工厂);}

有关演示，请参阅此 stackblitz.

I want to dynamically create a child component when the parent component is initialised, but when I tried to create it in ngAgterViewInit(), it throws the error that the ViewContainerRef is undefined.

component.ts

  @ViewChild('container', {read: ViewContainerRef}) container: ViewContainerRef;

  constructor(private resolver: ComponentFactoryResolver) {
  }

  ngAfterViewInit(){
    const factory = this.resolver.resolveComponentFactory(ChildComponent);
    this.container.createComponent(factory); //container is undefined here

  }

component.html

...
<div class="row" #container ></div>
...

解决方案

Since the div is inside an ngIf conditional block, it may not be available in ngAfterViewInit. You can protect the code against that possibility by monitoring the presence of the element with ViewChildren and the QueryList.changes event:

@ViewChildren('container', { read: ViewContainerRef }) containers: QueryList<ViewContainerRef>;

ngAfterViewInit() {
  if (this.containers.length > 0) {
    // The container already exists
    this.addComponent();
  };

  this.containers.changes.subscribe(() => {
    // The container has been added to the DOM
    this.addComponent();
  });
}

private addComponent() {
  const container = this.containers.first;
  const factory = this.resolver.resolveComponentFactory(ChildComponent);
  container.createComponent(factory);
}

See this stackblitz for a demo.

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