服务：typeof 不可分配给类型“Provider[]”

Question

我收到错误： 尝试在提供程序中使用“useClass：ApidataService”或“ApidataService”，并从服务构造函数中删除公共。

编译失败。

C:/wamp64/www/angular/project/src/app/app.module.ts (33,69): Argument of type '{ declarations: (typeof AppComponent | typeof ViewComponent | typeof AboutComponent | typeof News...' is not assignable to parameter of type 'NgModule'.
  Types of property 'providers' are incompatible.
    Type '{ provide: InjectionToken<string>; useValue: string; ApidataService: typeof ApidataService; }[]' is not assignable to type 'Provider[]'.
      Type '{ provide: InjectionToken<string>; useValue: string; ApidataService: typeof ApidataService; }' is not assignable to type 'Provider'.
        Object literal may only specify known properties, and 'ApidataService' does not exist in type 'Provider'.

我的服务是：

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

@Injectable()
export class ApidataService {

  public  constructor() { }
    cars = ['cars','bycycle','van'];
    mydata(){
        return "this is from apidata";
    }
}

还有app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';

import { AppComponent } from './app.component';
import { ViewComponent } from './view/view.component';
import { AboutComponent } from './about/about.component';
import { RouterModule, Routes} from '@angular/router';
import { NewsComponent } from './news/news.component';
import {APP_BASE_HREF} from '@angular/common';
import { FormsModule } from '@angular/forms';   //for 2way binding

//SERVICES SAMPLE
import {ApidataService} from './apidata.service';

@NgModule({
  declarations: [
    AppComponent,
    ViewComponent,
    AboutComponent,
    NewsComponent    
  ],
  imports: [
    HttpModule,
    BrowserModule,
    FormsModule,
    RouterModule.forRoot([
        {path:'About',component:AboutComponent},
        {path:'News',component:NewsComponent}
    ])
  ],
    providers: [
        {provide: APP_BASE_HREF, useValue: 'http://localhost:4200/',ApidataService}
     ],
  bootstrap: [AppComponent]
})

export class AppModule { }

Answer 1

使用

useClass

将类添加到提供者

providers: [
        {provide: APP_BASE_HREF, useValue: 'http://localhost:4200/', useClass: ApidataService}
 ],

Answer 2

必须将 ApidataService 添加为提供商列表中的第二项，如下所示：

providers: [
        { provide: APP_BASE_HREF, useValue: 'http://localhost:4200/' },
        { provide: ApidataService, useClass: ApidataService }
     ],

或更短：

providers: [
        { provide: APP_BASE_HREF, useValue: 'http://localhost:4200/' },
        ApidataService
     ],