Angular no provider for NameService

问题

I've got a problem loading a class into an Angular component. I've been trying to solve it for a long time; I've even tried joining it all in a single file. What I have is:

Application.ts

/// <reference path="../typings/angular2/angular2.d.ts" />

import {Component,View,bootstrap,NgFor} from "angular2/angular2";
import {NameService} from "./services/NameService";

@Component({
    selector:'my-app',
    injectables: [NameService]
})
@View({
    template:'<h1>Hi {{name}}</h1>' +
    '<p>Friends</p>' +
    '<ul>' +
    '   <li *ng-for="#name of names">{{name}}</li>' +
    '</ul>',
    directives:[NgFor]
})

class MyAppComponent
{
    name:string;
    names:Array<string>;

    constructor(nameService:NameService)
    {
        this.name = 'Michal';
        this.names = nameService.getNames();
    }
}
bootstrap(MyAppComponent);

services/NameService.ts

export class NameService {
    names: Array<string>;
    constructor() {
        this.names = ["Alice", "Aarav", "Martín", "Shannon", "Ariana", "Kai"];
    }
    getNames()
    {
        return this.names;
    }
}

I keep getting an error message saying No provider for NameService.

Can someone help me spot the issue with my code?

回答1:

You have to use providers instead of injectables

@Component({
    selector: 'my-app',
    providers: [NameService]
})

Complete code sample here.

回答2:

In Angular 2 there are three places you can "provide" services:

bootstrap
root component
other components or directives

"The bootstrap provider option is intended for configuring and overriding Angular's own preregistered services, such as its routing support." -- reference

If you only want one instance of NameService across your entire app (i.e., Singleton), then include it in the providers array of your root component:

@Component({
   providers: [NameService],
   ...
)}
export class AppComponent { ... }

Plunker

If you would rather have one instance per component, use the providers array in the component's configuration object instead:

@Component({
   providers: [NameService],
   ...
)}
export class SomeOtherComponentOrDirective { ... }

See the Hierarchical Injectors doc for more info.

回答3:

As of Angular 2 Beta:

Add @Injectable to your service as:

@Injectable()
export class NameService {
    names: Array<string>;

    constructor() {
        this.names = ["Alice", "Aarav", "Martín", "Shannon", "Ariana", "Kai"];
    }

    getNames() {
        return this.names;
    }
}

and to your component config add the providers as:

@Component({
    selector: 'my-app',
    providers: [NameService]
})

回答4:

You should be injecting NameService inside providers array of your AppModule's NgModule metadata.

@NgModule({
   imports: [BrowserModule, ...],
   declarations: [...],
   bootstrap: [AppComponent],
   //inject providers below if you want single instance to be share amongst app
   providers: [MyService]
})
export class AppModule {

}

If you want to create an Dependency for particular component level without bothering about state of your application, then you can inject that dependency on component providers metadata option like accepted @Klass answer shown.

回答5:

You should be injecting NameService inside providers array of your AppModule's NgModule metadata.

@NgModule({
   providers: [MyService]
})

and be sure import in your component by same name (case sensitive),becouse SystemJs is case sensitive (by design). If you use different path name in your project files like this:

main.module.ts

import { MyService } from './MyService';

your-component.ts

import { MyService } from './Myservice';

then System js will make double imports

回答6:

In Angular v2 and up it is now:

@Component({ selector:'my-app', providers: [NameService], template: ... })

回答7:

Shockingly, the syntax has changed yet again in the latest version of Angular :-) From the Angular 6 docs:

Beginning with Angular 6.0, the preferred way to create a singleton services is to specify on the service that it should be provided in the application root. This is done by setting providedIn to root on the service's @Injectable decorator:

src/app/user.service.0.ts

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

@Injectable({
  providedIn: 'root',
})
export class UserService {
}

回答8:

Angular 2 has changed, here is what the top of your code should look like:

import {
  ComponentAnnotation as Component,
  ViewAnnotation as View, bootstrap
} from 'angular2/angular2';
import {NameService} from "./services/NameService";

@Component({
  selector: 'app',
  appInjector: [NameService]
})

Also, you may want to use getters and setters in your service:

export class NameService {
    _names: Array<string>;
    constructor() {
        this._names = ["Alice", "Aarav", "Martín", "Shannon", "Ariana", "Kai"];
    }
    get names() {
        return this._names;
    }
}

Then in your app you can simply do:

this.names = nameService.names;

I suggest you go to plnkr.co and create a new Angular 2 (ES6) plunk and get it to work in there first. It will set everything up for you. Once it's working there, copy it over to your other environment and triage any issues with that environment.

回答9:

The error No provider for NameService is a common issue that many Angular2 beginners face.

Reason: Before using any custom service you first have to register it with NgModule by adding it to the providers list:

Solution:

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

回答10:

You could also have the dependencies declared in the bootstrap-command like:

bootstrap(MyAppComponent,[NameService]);

At least that's what worked for me in alpha40.

this is the link: http://www.syntaxsuccess.com/viewarticle/dependency-injection-in-angular-2.0

回答11:

Hi , You can use this in your .ts file :

first import your service in this .ts file:

import { Your_Service_Name } from './path_To_Your_Service_Name';

Then in the same file you can add providers: [Your_Service_Name] :

 @Component({
      selector: 'my-app',
      providers: [Your_Service_Name],
      template: `
        <h1>Hello World</h1> `   
    })

回答12:

Add it to providers not injectables

@Component({
    selector:'my-app',
    providers: [NameService]
})

回答13:

You need to add it to providers array, which includes all depency on your component.

Look at this section in angular documentation:

Registering providers in a component

Here's a revised HeroesComponent that registers the HeroService in its providers array.

import { Component } from '@angular/core';

import { HeroService } from './hero.service';

@Component({
  selector: 'my-heroes',
  providers: [HeroService],
  template: `
  <h2>Heroes</h2>
  <hero-list></hero-list>
  `
})
export class HeroesComponent { }

When to use NgModule versus an application component

On the one hand, a provider in an NgModule is registered in the root injector. That means that every provider registered within an NgModule will be accessible in the entire application.

On the other hand, a provider registered in an application component is available only on that component and all its children.

Here, the APP_CONFIG service needs to be available all across the application, so it's registered in the AppModule @NgModule providers array. But since the HeroService is only used within the Heroes feature area and nowhere else, it makes sense to register it in the HeroesComponent.

Also see "Should I add app-wide providers to the root AppModule or the root AppComponent?" in the NgModule FAQ.

So in your case, simply change injectables to providers like below:

@Component({
  selector: 'my-app',
  providers: [NameService]
})

Also in the new versions of Angular, @View and some other stuffs gone.

For more info ,visit here.

回答14:

add your service to providers[] array in app.module.ts file. Like below

// here my service is CarService

app.module.ts

import {CarsService} from './cars.service';

providers: [CarsService] // you can include as many services you have

回答15:

In Angular you are able to register a service in two ways:

1. Register a service in module or root component

Effects:

Available into all components
Available on lifetime application

You should take care if you register a service into a lazy loaded module:

The service is available only into components declared into that module
The service will be available on lifetime application only when the module is loaded

2. Register a service into any other application component

Effects:

Will be injected a separate instance of the Service into the component

You should take care if you register a service into any other application component

The instance of the injected service will be available only into the component and all of its children.
The instance will be available on the component lifetime.

回答16:

Angular2 requires you to declare all the injectables in bootstrap function call. Without this your service is not an injectable object.

bootstrap(MyAppComponent,[NameService]);

回答17:

Add @Injectable to your service as:

export class NameService {
    names: Array<string>;

    constructor() {
        this.names = ["Alice", "Aarav", "Martín", "Shannon", "Ariana", "Kai"];
    }

    getNames() {
        return this.names;
    }
}

and in your component add the providers as:

@Component({
    selector: 'my-app',
    providers: [NameService]
})

or if you want to access your service all over the application you can pass in app provider

回答18:

Blockquote

Registering providers in a component

Here's a revised HeroesComponent that registers the HeroService in its providers array.

import { Component } from '@angular/core';

import { HeroService } from './hero.service';

@Component({
  selector: 'my-heroes',
  providers: [HeroService],
  template: `
  `
})
export class HeroesComponent { }

来源：https://stackoverflow.com/questions/30580083/angular-no-provider-for-nameservice

标签

typescript

angular

systemjs