The ComponentFactory<any> 'DynamicComponent' cannot be associated with undefined

After researching how to render an MVC View into Angular 2, I came across this helpful directive

export function createComponentFactory(compiler: Compiler, metadata: Component): Promise<ComponentFactory<any>> {
  const cmpClass = class DynamicComponent {};
  const decoratedCmp = Component(metadata)(cmpClass);

  @NgModule({ imports: [CommonModule, RouterModule], declarations: [decoratedCmp] })
  class DynamicHtmlModule { }

  return compiler.compileModuleAndAllComponentsAsync(DynamicHtmlModule)
    .then((moduleWithComponentFactory: ModuleWithComponentFactories<any>) => {
      return moduleWithComponentFactory.componentFactories.find(x => x.componentType === decoratedCmp);
    });
}

Everything was working fine and my View was rendering as expected. However, after a few seconds, an error appeared.

https://i.sstatic.net/ZMPJs.jpg

This is the code for my component:

 import {
    Component,
    Directive,
    NgModule,
    Input,
    ViewContainerRef,
    Compiler,
    ComponentFactory,
    ModuleWithComponentFactories,
    ComponentRef,
    ReflectiveInjector, OnInit, OnDestroy, Type
} from '@angular/core';

import { RouterModule } from '@angular/router';
import { CommonModule } from '@angular/common';
import { Http } from "@angular/http";
import 'rxjs/add/operator/map';

export function createComponentFactory(compiler: Compiler, metadata: Component): Promise<ComponentFactory<any>> {   
    const cmpClass = class DynamicComponent { };
    const decoratedCmp = Component(metadata)(cmpClass);

    @NgModule({ imports: [CommonModule, RouterModule], declarations: [decoratedCmp] })
    class DynamicHtmlModule { }

    return compiler.compileModuleAndAllComponentsAsync(DynamicHtmlModule)
        .then((moduleWithComponentFactory: ModuleWithComponentFactories<any>) => {
            return moduleWithComponentFactory.componentFactories.find(x => x.componentType === decoratedCmp);
        });
}

@Directive({ selector: 'mvc-partial' })
export class RenderingViewDynamic implements OnInit, OnDestroy {
    html: string = '<p></p>';
    @Input() url: string;
    cmpRef: ComponentRef<any>;

    constructor(private vcRef: ViewContainerRef, private compiler: Compiler, private http: Http) { }

    ngOnInit() {
        this.http.get(this.url)
            .map(res => res.text())
            .subscribe(
            (html) => {
                this.html = html;
                if (!html) return;

                if (this.cmpRef) {
                    this.cmpRef.destroy();
                }

                const compMetadata = new Component({
                    selector: 'dynamic-html',
                    template: this.html,
                });

                createComponentFactory(this.compiler, compMetadata)
                    .then(factory => {
                        const injector = ReflectiveInjector.fromResolvedProviders([], this.vcRef.parentInjector);
                        this.cmpRef = this.vcRef.createComponent(factory, 0, injector, []);
                    });
            },
            err => console.log(err),
            () => console.log('MvcPartial complete')
            );

    }

    ngOnDestroy() {
        if (this.cmpRef) {
            this.cmpRef.destroy();
        }
    }
}

Can anyone suggest a solution for overcoming this issue?

Answer №1

It seems the issue lies in the method you have defined to return

Promise<ComponentFactory<any>>
. However, within this method, you are using the find function which has the potential to return undefined:

The find() function returns the value of the first element in an array that meets a specified condition. If no such element is found, undefined is returned.

This is likely why TypeScript is generating an error. You can resolve this by updating your method signature as follows:

createComponentFactory(...): `Promise<ComponentFactory<any>> | Promise<undefined>` { ... }

A similar situation exists here:

this.cmpRef = this.vcRef.createComponent(factory, 0, injector, []);
                    });

The createComponent function expects only a ComponentFactory<C>, yet your implementation allows for the possibility of passing undefined. Consider adding a check to ensure the factory exists, or if you are certain it will never be undefined, utilize the non-null assertion operator.

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