模块中声明的InjectionToken的@Inject()在angular2中失败

问题描述

最近我遇到了在模块中声明的InjectionToken的问题

Recently I've run into problem with InjectionToken, that is declared in module

import {InjectionToken, NgModule} from '@angular/core';
import {SampleComponent} from './sample.component';

export let SOME_TOKEN = new InjectionToken<string>('someToken');

@NgModule({
  declarations: [SampleComponent],
  providers: [
    {provide: SOME_TOKEN, useValue: 'Some value'}
  ]
})
export class SampleModule {
}

和组件类:

import {Component, Inject, OnInit} from '@angular/core';
import {SOME_TOKEN} from './sample.module';

@Component({
  selector: 'sample-component',
  templateUrl: './sample.component.html',
  styleUrls: ['./sample.component.scss']
})
export class SampleComponent implements OnInit {

  constructor(@Inject(SOME_TOKEN) private someValue: string) { }

  ngOnInit() {
    console.log(this.someValue);
  }

}

所有这些给我一个错误:未捕获的错误:无法解析SampleComponent的所有参数:(?).

All this gives me an error:Uncaught Error: Can't resolve all parameters for SampleComponent: (?).

同时，如果我尝试使用string作为在模块中声明的令牌，则一切正常.

At the same time if I try to use string as a token, that declared in module, everything works.

另外，如果我直接在组件文件中声明InjectionToken，然后直接在组件装饰器中设置"providers"，那么一切都会再次起作用.

Also, if I declare InjectionToken directly at component file, and then set 'providers' directly inside component decorator, everything works again.

所以问题是:为什么在模块文件中声明的InjectionToken无法用于注入组件.

So the question is: why InjectionToken that is declared inside module file is not available for injection to component.

推荐答案

根据@yurzui，存在循环依赖关系.将令牌移动到单独的文件有帮助.

According to @yurzui, there is a circular dependency.Moving token to separate file helped.

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