angular - 如何有条件地将服务注入(inject)组件？

Question

我有 2 个服务 one.service.ts 和 two.service.ts，以及一个组件 dashboard.component.ts。

如何有条件地将那些服务注入(inject)到组件中？

import { Component, ViewEncapsulation, Inject } from '@angular/core';
import { OneService } from '../services/one.service';
import { TwoService } from '../services/two.service';

@Component({
  selector: 'dashboard',
  encapsulation: ViewEncapsulation.Emulated,
  styleUrls: ['./dashboard.less'],
  templateUrl: './dashboard.html'
})
export class DashboardComponent {
    constructor() {
       // Here how do I get service instance based on some this condition.
         if(true) {
             /* Service **one.service.ts** to be injected */
         } else {
             /* Service **two.service.ts** to be injected */    
         }

    }
}

Answer 1

您可以使用Injector

import { Injector } from '@angular/core'  
...
constructor(private injector: Injector){ 

  if(true) {
    this.oneService = <OneService>this.injector.get(OneService);
  } else {
    this.twoService = <TwoService>this.injector.get(TwoService);
  }
}

正如@MeirionHughes 提到的，这称为服务定位器模式:

The technique is an example of the service locator pattern.

Avoid this technique unless you genuinely need it. It encourages a careless grab-bag approach such as you see here. It's difficult to explain, understand, and test. You can't know by inspecting the constructor what this class requires or what it will do. It could acquire services from any ancestor component, not just its own. You're forced to spelunk the implementation to discover what it does.

Framework developers may take this approach when they must acquire services generically and dynamically.

来源:https://angular.io/docs/ts/latest/guide/dependency-injection.html#!#explicit-injector

再次如前所述，您可以在另一个服务中获取这些注入(inject)器，然后将此服务注入(inject)到您的组件中。