Dynamically adding components in ngFor

问题:

I have a "dashboard" that loads configured elements. Dashboard template has this:

  <div class="dash-container" [ngGrid]="gridConfig">
    <div *ngFor="let box of boxes; let i = index"
       [(ngGridItem)]="box.config"
       (onItemChange)="updateItem(i, $event)"
       (onResize)="onResize(i, $event)"
       (onDrag)="onDrag(i, $event)"
       (onDragStop)="onDragStop(i,$event)"
       [ngClass]="box.class"
     >
      <div class="handle"><h4>{{box.title}}</h4></div>
      <div [innerHTML]= "box.content"></div>
    </div>
  </div>

Now <div [innerHTML]= "box.content"></div> will not work because non standard elements get sanitised. Running latest Angular 2.4.6 (RC 6).

I look at the examples i could find for dynamic components - but all i see is that they just add components to the current component - but i need them in a very specific divs like in the example above.

ComponentFactoryResolver is often used together with @ViewChild. But i can't just do this inside a loop:

ngAfterViewInit() {
    const dashWidgetsConf = this.widgetConfigs();
    for (var i = 0; i < dashWidgetsConf.length; i++) {
      const conf = dashWidgetsConf[i];

      @ViewChild(conf.id, {read: ViewContainerRef}) var widgetTarget: ViewContainerRef;

      var widgetComponent = this.componentFactoryResolver.resolveComponentFactory(UnitsComponent);
      widgetTarget.createComponent(widgetComponent);
    }
  }

The @viewchild gives 'Decorators are not valid here'. How can i load components from a conf list (in a loop) and add them inside a specific div (divs got #{{conf.id}}) in my component?

回答1:

After some research, this is the solution i came up with (works in angular 4.0.0).

Load all the ViewContainerRef targets by id:

@ViewChildren('dynamic', {read: ViewContainerRef}) public widgetTargets: QueryList<ViewContainerRef>;

Then loop over them to get the target, create a factory for the component and call createComponent.
Also can use the component reference to subscribe or set other component properties.

ngAfterViewInit() {
    const dashWidgetsConf = this.widgetConfigs();
    const widgetComponents = this.widgetComponents();
    for (let i = 0; i < this.widgetTargets.toArray().length; i++) {
        let conf = dashWidgetsConf[i];
        let component = widgetComponents[conf.id];
        if(component) {
            let target = this.widgetTargets.toArray()[i];
            let widgetComponent = this.componentFactoryResolver.resolveComponentFactory(component);
            let cmpRef: any = target.createComponent(widgetComponent);

            if (cmpRef.instance.hasOwnProperty('title')) {
                cmpRef.instance.title = conf.title;
            }
        }
    }
}

The widgetComponents is a object {key: component} and widgetConfigs is where i store specific component info - like title, component id etc.

Then in template:

<div *ngFor="let box of boxes; let i = index" >
    <ng-template #dynamic></ng-template>
</div>

And the order of targets is the same as in my conf ( boxes is generated from it) - which is why i can loop through them in order and use i as index to get the correct conf and component.

回答2:

After

if (cmpRef.instance.hasOwnProperty('title')) {
   cmpRef.instance.title = conf.title;
}

You can add this.cd.detectChanges(); or you will have the error "ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked" in your children component with Angular 6x.

回答3:

If you have this pattern:

<div *ngFor="for item in items">
  <!-- needs to be one per item -->
  <ng-template details-directive></ng-template>
</div>

I suggest wrapping the directive in a component:

@Component({
  selector: 'details-wrapper',
  template: '<ng-template details-directive></ng-template>'
})
export class DetailsWrapper {
  @Input item?: Item;
  // Dynamically load details using the regular solution.
}

And making this your for loop:

<div *ngFor="for item in items">
  <details-wrapper [item]="item"></details-wrapper>
</div>