angular2中没有提供服务错误的提供程序，为什么我需要将其注入到其父组件中? [英] No provider for service error in angular2, why do I need to inject it in it's parent component?

问题描述

我有一个pages.service.ts

I have a pages.service.ts

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

import { ApiService } from '../../apiService/api.service';

import { Playlists } from '../shared/playlists.model';


@Injectable()
export class PagesService {

  private currentPlaylists: Subject<Playlists> = new BehaviorSubject<Playlists>(new Playlists());

  constructor(private service: ApiService) {

  }


}

此页面服务需要另一个名为 ApiService 的服务，我按上面所示的方式进行了注入，

This pages service needs another service called ApiService, I inject the way as shown above, it works.

我在main.ts中引导ApiService

I bootstrap ApiService in main.ts

import { ApiService }  from './apiService/api.service';
import { AppComponent } from './app.component';

bootstrap(AppComponent,[
  disableDeprecatedForms(),
  provideForms(),
  HTTP_PROVIDERS,
  ROUTER_PROVIDERS,
  ApiService
]).catch((err: any) => console.error(err));;

但是，当我尝试将 PagesService 注入另一个组件时，出现了错误，即 PagesService 没有提供程序.

But When I try to inject the PagesService to another component, it gives me error, No Provider for PagesService.

我这样写该组件.

    import { Component, ViewChild, ElementRef, Input, Output, EventEmitter } from '@angular/core';
    import { CORE_DIRECTIVES } from '@angular/common';

    import { MODAL_DIRECTVES, BS_VIEW_PROVIDERS } from 'ng2-bootstrap/ng2-bootstrap';


    import { ApiService } from '../../apiService/api.service';
    import { PagesService } from '../../pages/shared/pages.service';


    @Component({
      selector: 'assign-playlist-modal',
      exportAs: 'assignModal',
      providers: [ PagesService ],
      directives: [MODAL_DIRECTVES, CORE_DIRECTIVES, FORM_DIRECTIVES, REACTIVE_FORM_DIRECTIVES ],
      viewProviders: [BS_VIEW_PROVIDERS],
      styleUrls: ['app/channel/shared/assignPlaylist.css'],
      templateUrl: 'app/channel/modals/assignPlaylistModal.html'
    })

    export class AssignPlaylistModalComponent {


      constructor(private apiService: ApiService, private pageService: PagesService, fb: FormBuilder) {
       }
}

更新:这是我的文件结构

channel/
--channel.component.ts
--shared/
----assignPlaylist.modal.ts
----addPlaylist.modal.ts
pages/
--shared/
----pages.service.ts
--pages.component.ts

Channel组件是addPlaylist的父级，addPlaylist是assignPlaylist的父级.这种结构不起作用

Channel component is the parent of addPlaylist, addPlaylist is the parent of assignPlaylist. This structure will not work

ChannelComponent       
       |
AddPlaylistComponent
       |
AssignPlaylistComponent     ----PagesService----ApiService

我找到了一个解决方案，但不知道为什么需要这样做，

我将提供程序'PagesService'添加到ChannelComponent，以及AssignPlaylistComponent，它将正常运行，没有错误.

I add the provider 'PagesService' to ChannelComponent, and also the AssignPlaylistComponent, it will work, no errors.

即使这行得通

ChannelComponent            ----PagesService-------------
       |
AddPlaylistComponent
       |
AssignPlaylistComponent     ----ApiService---------------

但是，我只想在AssignPlaylistComponent中使用PagesService，所以我认为在channelcomponent.ts中导入PagesService并在其中创建providers数组是没有意义的.

However, I just want to use PagesService in AssignPlaylistComponent, so I think it not make sense to import PagesService in channelcomponent.ts and make a providers array in it.

推荐答案

这有点奇怪，但是只有组件可以在Angular中配置依赖项注入(好了，bootstrap()).即，只有组件可以指定提供程序.

It is a bit strange, but only components can configure dependency injection in Angular (well, and bootstrap()). I.e., only components can specify providers.

如果组件树中指定了providers数组，则组件树中的每个组件都将获得一个关联的注入器".我们可以将其视为注入器树，(通常比组件树稀疏).当需要解决依赖关系时(通过组件或服务)，将查询该注入器树.可以满足依赖性的第一个喷油器就这样做了.进样器树向根组件/进样器走去.

Each component in the component tree will get an associated "injector" if the component has a providers array specified. We can think of this like an injector tree, that is (normally much) sparser than the component tree. When a dependency needs to be resolved (by a component OR a service), this injector tree is consulted. The first injector that can satisfy the dependency does so. The injector tree is walked up, toward the root component/injector.

因此，为了让您的PagesService注入ApiService依赖项，必须首先向该注入器注册该ApiService对象.即在组件的providers数组中.此注册必须在您要使用/注入ApiService的组件处或上方的某个位置进行.

So, in order for your PagesService to inject a ApiService dependency, that ApiService object first has to be registered with an injector. I.e., in a component's providers array. This registration must occur somewhere at or above the component where you want to use/inject the ApiService .

您的服务随后应该能够注入已注册的ApiService对象，因为它将在注入器树中找到它.

Your service should then be able to inject the registered ApiService object, because it will find it in the injector tree.

另请参见 Angular 2-在服务中包含提供者.

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