Angular 4依赖注入学习教程之ValueProvider的使用（七）

const provider: ValueProvider = {provide: 'someToken', useValue: 'someValue'};

export interface ValueProvider {
 // 用于设置与依赖对象关联的Token值，Token值可能是Type、InjectionToken、
 // OpaqueToken的实例或字符串
 provide: any;
 // 设置注入的对象
 useValue: any;
 // 用于标识是否multiple providers，若是multiple类型，则返回与Token关联的依赖
 // 对象列表
 multi?: boolean;
}

npm install -g json-server

json-server --watch db.json

{
 "/heros": {
 "target": "http://localhost:3000",
 "secure": false
 }
}

{
 "scripts": {
 "start": "ng serve --proxy-config proxy.conf.json",
 }
}

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

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

import { LoggerService } from './logger.service';

@Injectable()
export class HeroService {
 constructor(private loggerService: LoggerService,
 private http: Http) { }

 apiUrl = 'http://localhost:4200/heros';

 getHeros(): Observable<Array<{ id: number; name: string }>> {
 this.loggerService.log('Fetching heros...');
 return this.http.get(this.apiUrl)
  .map(res => res.json())
 }
}

import { Component, OnInit } from '@angular/core';
import { HeroService } from '../hero.service';
import { LoggerService } from '../logger.service';

@Component({
 selector: 'app-hero',
 template: `
 <ul>
 <li *ngFor="let hero of heros">
 ID: {{hero.id}} - Name: {{hero.name}}
 </li>
 </ul>
 `
})
export class HeroComponent implements OnInit {
 heros: Array<{ id: number; name: string }>;

 constructor(private heroService: HeroService,
 private loggerService: LoggerService) { }

 ngOnInit() {
 this.loggerService.log('Fetching heros...');
 this.heroService.getHeros()
 .subscribe(res => {
 this.heros = res;
 });
 }
}

{
 "heros": [
 {"id":11,"name":"Mr. Nice"},
 {"id":12,"name":"Narco"},
 {"id":13,"name":"Bombasto"},
 {"id":14,"name":"Celeritas"},
 {"id":15,"name":"Magneta"}
 ]
}

json-server --watch heros.json

\{^_^}/ hi!

Loading heros.json
Done

ID: 11 - Name: Mr. Nice
ID: 12 - Name: Narco
ID: 13 - Name: Bombasto
ID: 14 - Name: Celeritas
ID: 15 - Name: Magneta

@Injectable()
export class HeroService {
 ...
 apiUrl = 'http://localhost:4200/heros';
}

@NgModule({
 ...,
 providers: [
 {
 provide: 'apiUrl',
 useValue: 'http://localhost:4200/heros'
 }
 ],
 bootstrap: [AppComponent]
})
export class AppModule { }

@Injectable()
export class HeroService {
 constructor(private loggerService: LoggerService,
 private http: Http,
 @Inject('apiUrl') private apiUrl) { }

 getHeros(): Observable<Array<{ id: number; name: string }>> {
 this.loggerService.log('Fetching heros...');
 return this.http.get(this.apiUrl)
  .map(res => res.json())
 }
}

ID: 11 - Name: Mr. Nice
ID: 12 - Name: Narco
ID: 13 - Name: Bombasto
ID: 14 - Name: Celeritas
ID: 15 - Name: Magneta

constructor(@Inject(Http) private http) { }

constructor(@Inject(Http) private http: Http) { }

[ts] Parameter 'http' implicitly has an 'any' type.

constructor(private http: Http) { }