遇到未定义的提供者！ 通常这意味着你有一个循环依赖（可能是由使用“桶” index.ts 文件引起的

Question

Browser Error :

    Error: Encountered undefined provider! Usually this means you have a circular dependencies (might be caused by using 'barrel' index.ts files.
  Evaluating http://localhost:3000/app/boot.js
  Loading app/boot
    at syntaxError (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:1513:34)
    at eval (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14410:40)
    at Array.forEach (native)
    at CompileMetadataResolver._getProvidersMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14395:19)
    at CompileMetadataResolver.getNgModuleMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14051:50)
    at JitCompiler._loadModules (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:25088:64)
    at JitCompiler._compileModuleAndComponents (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:25047:52)
    at JitCompiler.compileModuleAsync (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:25009:21)
    at PlatformRef_._bootstrapModuleWithZone (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:4793:25)
    at PlatformRef_.bootstrapModule (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:4779:21)
(anonymous) @ gmapp:18
ZoneDelegate.invoke @ zone.js:391
Zone.run @ zone.js:141
(anonymous) @ zone.js:818
ZoneDelegate.invokeTask @ zone.js:424
Zone.runTask @ zone.js:191
drainMicroTaskQueue @ zone.js:584

app.module.ts : module ts file

    import { NgModule }      from '@angular/core';
    import { BrowserModule } from '@angular/platform-browser';
    import { HttpModule }    from '@angular/http';
    import { RouterModule, Routes } from '@angular/router';
    import { myService } from 'app/httpServices/my.service';
    import { AppComponent }  from './app.component';
    import { gmappComponent } from './gmappComponent/gmapp.component';


    const appRoutes: Routes = [
      { path: 'gmapp', component: gmappComponent }

    ];

@NgModule({
  imports:      [ BrowserModule,RouterModule.forRoot(appRoutes),HttpModule ],
  providers: [ myService ],
  declarations: [ AppComponent , gmappComponent ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

app.component.ts : component code

import {  Component } from '@angular/core';
import { myService } from 'app/httpServices/my.service';

@Component({
  selector: 'my-app',
  template: `
            <h1>Angular2</h1><p>Hello {{test}} {{name}}</p>
            <ul class="nav nav-tabs nav-justified">
              <li role="presentation" class="active"><a routerLink="/mapp" routerLinkActive="active">mapp</a></li>
              <li role="presentation"><a href="#">gap</a></li>
              <li role="presentation"><a href="#">pst</a></li>
            </ul>

            <router-outlet></router-outlet>
  `,
  provider : [myService]
})

export class AppComponent {
  test: string;
  name: string;

  constructor() {
    this.test = "Prav";
    this.name = "S";
  }
}

gmapp.component.ts : another component

import { Component } from '@angular/core';
import { MyService } from 'app/httpServices/my.service';

@Component({
  templateUrl : './gmapp.html',
  provider: [MyService]
})


export class gmappComponent {
   servercount : number;
   name : string ;
   MyArrayType : any[];
    profile = {};

   constructor(private myService: MyService) {

     this.servercount = 30;

   }

   loadUser() {
     this.myService.getUser().subscribe(data => this.profile = data);
   }
 }

my.service.ts :

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import 'node_modules/rxjs/add/operator/map';

@Injectable()
export class MyService {
  constructor (
    private http: Http
  ) {}

  getUser() {
    return this.http.get(`https://abcd.com/abcd`)
    .map((res:Response) => res.json());
  }

}

above are my code files , please check and let me know if I'm doing anything wrong over there.

Answer 1

Provider name should be name of service and it should be in same case.

Service

@Injectable()
export class MyService {

}

So, myService need to replace with MyService in my-app component and app.module.

Provider

@Component({ selector: 'my-app',   
             template: ``,   
             provider : [myService] })

Providers

providers: [ myService ]

Answer 2

I had the same issue, but on my case i removed "storage" from providers

@NgModule({
providers: [ storage, ... ]
})

in app.module.ts since @ionic/storage 2.xx we import IonicStorageModule instead of storage