Angular 2 HTTP “Cannot resolve all parameters for 'AppService'”

问题

I tried to import the http provider into a service, but I'm getting the following error:

Cannot resolve all parameters for 'AppService'(?). Make sure that all the parameters are decorated with Inject or have valid type annotations and that 'AppService' is decorated with Injectable.

Here are some code snippets:

<script src="~/es6-shim/es6-shim.min.js"></script>
<script src="~/systemjs/dist/system-polyfills.js"></script>

<script src="~/angular2/bundles/angular2-polyfills.js"></script>
<script src="~/systemjs/dist/system.src.js"></script>
<script src="~/rxjs/bundles/Rx.js"></script>
<script src="~/angular2/bundles/angular2.dev.js"></script>
<script src="~/angular2/bundles/http.dev.js"></script>

<!-- 2. Configure SystemJS -->
<script>
    System.config({
        map: { 'rxjs': 'RCO/rxjs' },
        packages: {
            RCO: {
                format: 'register',
                defaultExtension: 'js'
            },
            'rxjs': {defaultExtension: 'js'}
        }
    });
  System.import('RCO/Areas/ViewOrganization/AngularTemplates/boot')
      .then(null, console.error.bind(console));

boot.ts

import {bootstrap} from 'angular2/platform/browser'
import {HTTP_PROVIDERS} from 'angular2/http'
import 'rxjs/add/operator/map'
import {AppComponent} from  'RCO/Areas/ViewOrganization/AngularTemplates/app.component'
import {AppService} from 'RCO/Areas/ViewOrganization/AngularTemplates/app.service'

bootstrap(AppComponent, [HTTP_PROVIDERS, AppService]);

app.service.ts

import {Injectable} from 'angular2/core';
import {Http, Response} from 'angular2/http';
import {Observable} from 'rxjs/Rx';

@Injectable()
export class AppService {

    constructor(private http: Http) { }

    // Uses http.get() to load a single JSON file
    getTableData() {
        return this.http.get('...').map((res: Response) => res.json());
    }

}

I'm trying to call a controller on the server to eventually load a JSON file into a data table. Pretty straightforward stuff, but the way I'm loading the Http modules seems to be wrong. Any help will be much appreciated.

回答1:

Seems like you are not using typescript compiler for transpiling files to js, In that case you need to have use @Inject while injecting any dependency inside a component constructor.

import {Injectable, Inject} from 'angular2/core';
import {Http, Response} from 'angular2/http';
import {Observable} from 'rxjs/Rx';

@Injectable()
export class AppService {
    constructor(@Inject(Http) private http: Http) { }
    // Uses http.get() to load a single JSON file
    getTableData() {
        return this.http.get('...').map((res: Response) => res.json());
    }
}

回答2:

Another way to do it, which saves some typing in the future would be:

in your tsconfig.json add compilerOptions.emitDecoratorMetadata=true

example of simple tsconfig.json would be:

{
  "compilerOptions": {
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true
  }
}

回答3:

I had the same issue, and for me the problem was that i was missing import { HttpModule } from '@angular/http' in app.module.ts

回答4:

Another possible solution is that you are missing some polyfills. Anyone who had no luck with another answers should try to add this polyfill:

import 'core-js/es7/reflect';

来源：https://stackoverflow.com/questions/35370405/angular-2-http-cannot-resolve-all-parameters-for-appservice

标签

typescript

angular

systemjs

angular2-services

angular2-injection