文件

real.service.ts

import { Injectable } from '@angular/core';@Injectable()
export class RealService {data = {name: 'real service'}constructor() { }changeData(value: string= 'changed') {this.data.name = value;}
}

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';import { AppComponent } from './app.component';
import { FirstModule } from './first/first.module';
import { NormalService } from './service/normal.service';
import { RealService } from './service/real.service';
@NgModule({declarations: [AppComponent],imports: [BrowserModule,FirstModule],providers: [{provide: NormalService,useClass: RealService}],bootstrap: [AppComponent]
})
export class AppModule { }

别的代码和之前一致

运行效果

实际注入的service RealService

这个有什么用呢

有时项目分模块时可以先写一个假的service，方便独立开发

ps

如果service中还注入了其他service，可以加上注入项

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';import { AppComponent } from './app.component';
import { FirstModule } from './first/first.module';
import { NormalService } from './service/normal.service';
import { RealService } from './service/real.service';
@NgModule({declarations: [AppComponent],imports: [BrowserModule,FirstModule],providers: [{provide: NormalService,useClass: RealService，dep: [] //其他service}],bootstrap: [AppComponent]
})
export class AppModule { }