Angular 4 依赖注入学习教程之FactoryProvider的使用（四）

function serviceFactory() { 
 return new Service();
}

const provider: FactoryProvider = {
 provide: 'someToken', useFactory: serviceFactory, deps: []
};

export interface FactoryProvider {
 // 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;
 // 设置用于创建对象的工厂函数
 useFactory: Function;
 // 依赖对象列表
 deps?: 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;
}

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

 constructor(private heroService: HeroService) { }

 heros: Array<{ id: number; name: string }>;

 ngOnInit() {
 this.heros = this.heroService.getHeros();
 }
}

console.log('Fetching heros...');
this.heros = this.heroService.getHeros();

export class LoggerService {
 constructor(private enable: boolean) { }

 log(message: string) {
 if(this.enable) {
  console.log(`LoggerService: ${message}`);
 }
 }
}

@NgModule({
 ...
 providers: [
 HeroService,
 LoggerService
 ],
 bootstrap: [AppComponent]
})
export class AppModule { }

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.heros = this.heroService.getHeros();
 }
}

Uncaught Error: Can't resolve all parameters for LoggerService: (?).

ERROR Error: No provider for Boolean!

export class LoggerService {
 constructor(private enable: boolean) { }
 // ...
}

export function isType(v: any): v is Type<any> {
 return typeof v === 'function';
}

Uncaught Error: Can't resolve all parameters for LoggerService: (?).

@NgModule({
 ...,
 providers: [
 HeroService,
 {
 provide: LoggerService, 
 useFactory: () => {
 return new LoggerService(true);
 }
 }
 ],
 bootstrap: [AppComponent]
})
export class AppModule { }

LoggerService: Fetching heros...