Angular InjectionToken的一個具體使用例子

導入InjectionToken：

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

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調用從@Angular/core導入的構造器，建立一個新的執行個體：

export const TOKEN_HOST_CLASS_PROVIDER = new InjectionToken<HostTokenComponentService>('TOKEN_HOST_CLASS_PROVIDER');           

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Injection構造器的實作：

export declare class InjectionToken<T> {
    protected _desc: string;
    readonly ɵprov: never | undefined;
    constructor(_desc: string, options?: {
        providedIn?: Type<any> | 'root' | 'platform' | 'any' | null;
        factory: () => T;
    });
    toString(): string;
}           

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Component構造器裡的定義：

providers: [
    HostComponentService,
    {provide: TOKEN_HOST_CLASS_PROVIDER, useClass: HostTokenComponentService}
  ]           

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在Component 構造函數裡進行注入：

export class HostDecoratorComponent {

  
  constructor(private hostComponentService: HostComponentService, @Inject(TOKEN_HOST_CLASS_PROVIDER) h){
    console.log('in HostDecoratorComponent, Host component service got from own Injector: ', hostComponentService, ' HostTokenComponentService: ', h);
    h.print();
  }           

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最後運作結果：

調用InjectionToken構造器，options的值為undefined：