Angular ViewChildren不会立即从ngFor中看到所有子级

问题描述

我有一个@ViewChildren的奇怪行为，它对应于ngFor生成的子组件. @ViewChildren查询在很长一段时间内都看不到元素在数组中站立.我所有的代码都在 Plunker -在打开控制台的情况下进行查看.

I have a strange behaviour of @ViewChildren corresponding to children components generated by ngFor. @ViewChildren query does not see element standing in array for a quite long time. All my code is in the Plunker - see with console opened.

这是我的主要组成部分:

This is my main component:

@Component({
    selector: 'my-app',
    template: `
        <button (click)="addInternalComponent()">Add internal component</button>
        <app-internal #internals *ngFor="let i of indexes" [index]="i
(afterViewInit)="onAfterViewInit()"></app-internal>
    `,
})
export class App {
    @ViewChildren('internals') internals: QueryList<InternalComponent>;
    indexes = [];
    addInternalComponent() {
        console.log('adding internal component!');
        this.indexes.push(this.indexes.length);
        console.log('Not complete list', this.internals._results);

    }

    onAfterViewInit() {
        console.log('onAfterViewInit - still not complete list', this.internals._results);
    }
}

哪些子组件可以通过单击按钮添加.

Which has come children components that we can add by clicking a button.

在将元素添加到可以在ngFor循环中生成所有子代的indexs数组中之后-我们没有刚刚添加的那个子代.

After adding an element into indexes array that generates all children in ngFor loop - we don't have that one that we just have added.

我可以理解这种行为-因为子组件可能需要一些时间来创建它，并且引擎决定在创建完整子组件之前控制台日志.

I can understand that behaviour - because maybe child component needs some time to create it and engine decides to console log before creating full child component.

但是，我在子组件中创建了发射器，表示子视图和模型均已初始化.但是...在父组件中处理此事件-我们仍然不知何故没有此项.这怎么可能?

However I created emitter in child component signaling that both child's view and model are initialised. But... Handling this event in parent component - we still somehow doesn't have this item. How even is this possible?

子组件:

export class InternalComponent implements AfterViewInit {
  @Input()
  index;
  @Output()
  afterViewInit: EventEmitter<any> = new EventEmitter<any>();

  ngAfterViewInit() {
    this.afterViewInit.emit();
  }

}

推荐答案

用于通知QueryList的内容已更改为订阅ngAfterViewInit中changes事件的标准方法:

The standard way to be notified that the content of a QueryList has changed it to subscribe to its changes event in ngAfterViewInit:

@ViewChildren("internals") internals: QueryList<InternalComponent>;

ngAfterViewInit() {
  this.internals.changes.subscribe((list: QueryList<InternalComponent>) => {
    // The updated QueryList is available here (with list or with this.internals)
    this.doSomethingWithInternals(list);
    this.doSomethingWithNewInternal(list.last);
    ...
  });
}

---

上面的事件处理可能就是您所需要的.如果仍要在InternalComponent中实现afterViewInit事件，则可以将对组件的引用作为事件的参数传递:

---

The event handling above may be all you need. If you still want to implement the afterViewInit event in InternalComponent, you can pass a reference to the component as a parameter of the event:

export class InternalComponent implements AfterViewInit {
  @Output() afterViewInit = new EventEmitter<InternalComponent>();

  ngAfterViewInit() {
    this.afterViewInit.emit(this);
  }

}

并在事件处理程序中检索组件:

and retrieve the component in the event handler:

(afterViewInit)="onAfterViewInit($event)"

onAfterViewInit(component: InternalComponent) {
    this.useNewInternalComponent(component);
    ...
}

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