Getting dependency from Injector manually inside a directive

Question

I am trying to create a generic directive which will take a class type for rule validation and according to the rule in the class the directive will either show or hide an e

Answer 1

You need to pass the parent injector like

export class MyIfDirective {
  constructor(private injector:Injector, private _viewContainer: ViewContainerRef,
    private _template: TemplateRef<Object>) 
  { }

  @Input() set myIf(rule: string) {
    let resolvedProviders = ReflectiveInjector.resolve([AdminOnly]);
    let childInjector = ReflectiveInjector.fromResolvedProviders(resolvedProviders, this.injector);

    let adminOnly : IRule = childInjector.get(AdminOnly);
    let show = adminOnly.shouldShowElement();
    show ? this.showItem() : this.hideItem();
  }
  private showItem() {
    this._viewContainer.createEmbeddedView(this._template);
  }

  private hideItem() {
    this._viewContainer.clear();
  }
}

See also Inject service with ReflectiveInjector without specifying all classes in the dependency tree

Answer 2

Just update for Angular version 10+:

• From your service:

  @Injectable({
    providedIn: 'any'
  })
  export class AdminOnly { ... }

• In your directive or a pure function, ...:

 import { Injector } from '@angular/core';

 ...
 const injector: Injector = Injector.create({
   providers: [{provide: AdminOnly, deps: []}]
 });
 const adminOnly: AdminOnly = injector.get(AdminOnly);

 let show = adminOnly.shouldShowElement();
 ...

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