Angular 遇到未定义的提供程序！通常这意味着您具有循环依赖关系（可能是由于使用'；barrel'；index.ts文件引起的）

app.module.ts：模块ts文件

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.component.ts：组件代码

    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 { }

my.service.ts：

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);
   }
 }

---

以上是我的代码文件，请检查并让我知道我是否在那里做错了什么。

提供商名称应该是服务名称，并且应该是相同的大小写

服务

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());
  }

}

因此，我的应用程序组件和app.module中的

myService

需要替换为

myService

提供商

@Injectable()
export class MyService {

}

提供商

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

---

我也有同样的问题，但在我的案例中，我从提供者中删除了“存储”

providers: [ myService ]

在app.module.ts中 自@ionic/storage 2.x.x起

---

我们导入IonicStorageModule而不是storage

我看到至少两个错误，您在应用程序组件和模块中将

MyService

错误地命名为

MyService

。另外，如果您在应用程序模块中声明提供者，则不需要在组件中执行此操作。更大的错误是，您的

没有选择器>gmappComponent

…谢谢，现在工作正常

providers: [ myService ]

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