Angular 4 - Seeking clarification on the usage of *ngComponentOutlet

Question

Angular 4 - Seeking clarification on the usage of *ngComponentOutlet

When using *ngComponentOutlet, the following code snippets are employed to handle the displaying:

Below is a snippet of functional code:

this.displayComponent({
        'objects':[
                {component: ToDisplayAComponent, expanded: false},
                {component: ToDisplayBComponent, expanded: false}
                ]
    })

The array of objects will be iterated using *ngFor to display the components.

The desired functionality - passing different instances of the same abstract component initialized with unique properties - is not working as shown below:

let compA = new ToDisplayAComponent(aProperty);
let compB = new ToDisplayAComponent(anotherPropert);
this.displayComponent({
            'objects':[
                    {component: compA, expanded: false},
                    {component: compB, expanded: false}
                    ]
        });

In addition to a solution to the issue at hand, I am curious about why the above code does not function correctly.

PS. It compiles but throws the following error message:

ERROR Error: No component factory found for [object Object]. Did you add it to @NgModule.entryComponents?

angular typescript angular-directive

Answer 1

Answer №1

The Angular compiler scans the components specified in the entryComponents array of the @NgModule and generates factories for them. The ngComponentOutlet directive then utilizes the componentFactoryResolver to retrieve these factories and instantiate component objects. Below is an excerpt from the source code highlighting this process:

@Directive({selector: '[ngComponentOutlet]'})
export class NgComponentOutlet implements OnChanges, OnDestroy {
  @Input() ngComponentOutlet: Type<any>;

  ngOnChanges(changes: SimpleChanges) {
    ...
const componentFactory=componentFactoryResolver.resolveComponentFactory(this.ngComponentOutlet);
this._componentRef=this._viewContainerRef.createComponent(componentFactory,...)

If your first example is functioning correctly, it suggests that you have added both ToDisplayAComponent and ToDisplayBComponent to the entry components list as shown below:

@NgModule({
   entryComponents: [ ToDisplayAComponent, ToDisplayBComponent ]

In this scenario, when the componentOutlet requests a component like so:

resolveComponentFactory(this.ngComponentOutlet)

The variable this.ngComponentOutlet holds a reference to the class ToDisplayAComponent, aligning with the entries defined in entryComponents:

entryComponents[0] === this.ngComponentOutlet (ToDisplayAComponent)

However, in your second example, instead of passing class references, you are passing instances which do not correspond:

entryComponents[0] !== this.ngComponentOutlet (new ToDisplayAComponent())
                                              ^^^^^

This mismatch causes Angular to report an error stating no component factory was found in the entry components.

Your intention to pass custom parameters directly to the component class constructor cannot be achieved in this manner. This is because components are instantiated within the dependency injection context. If you need to pass specific data to a component, consider defining a provider instead.

For further insights on working with dynamic components, you can refer to this article: Here is what you need to know about dynamic components in Angular

Answer 2

The Angular compiler scans the components specified in the entryComponents array of the @NgModule and generates factories for them. The ngComponentOutlet directive then utilizes the componentFactoryResolver to retrieve these factories and instantiate component objects. Below is an excerpt from the source code highlighting this process:

@Directive({selector: '[ngComponentOutlet]'})
export class NgComponentOutlet implements OnChanges, OnDestroy {
  @Input() ngComponentOutlet: Type<any>;

  ngOnChanges(changes: SimpleChanges) {
    ...
const componentFactory=componentFactoryResolver.resolveComponentFactory(this.ngComponentOutlet);
this._componentRef=this._viewContainerRef.createComponent(componentFactory,...)

If your first example is functioning correctly, it suggests that you have added both ToDisplayAComponent and ToDisplayBComponent to the entry components list as shown below:

@NgModule({
   entryComponents: [ ToDisplayAComponent, ToDisplayBComponent ]

In this scenario, when the componentOutlet requests a component like so:

resolveComponentFactory(this.ngComponentOutlet)

The variable this.ngComponentOutlet holds a reference to the class ToDisplayAComponent, aligning with the entries defined in entryComponents:

entryComponents[0] === this.ngComponentOutlet (ToDisplayAComponent)

However, in your second example, instead of passing class references, you are passing instances which do not correspond:

entryComponents[0] !== this.ngComponentOutlet (new ToDisplayAComponent())
                                              ^^^^^

This mismatch causes Angular to report an error stating no component factory was found in the entry components.

Your intention to pass custom parameters directly to the component class constructor cannot be achieved in this manner. This is because components are instantiated within the dependency injection context. If you need to pass specific data to a component, consider defining a provider instead.

For further insights on working with dynamic components, you can refer to this article: Here is what you need to know about dynamic components in Angular

Angular 4 - Seeking clarification on the usage of *ngComponentOutlet

Answer №1

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