How to create an Http instance WITHOUT using const

问题:

This question already has an answer here:

• angular2 resolveAndCreate HTTP - missing HTTP_PROVIDERS in RC7 1 answer

I need to get an instance of Http without using Angular2's DI ( constructor(private http: Http) )

The following code was taken from another stackoverflow question, and it works in Angular2 RC.4 and earlier versions, but not in RC.5+(HTTP_PROVIDERS is no longer available) :

const injector = ReflectiveInjector.resolveAndCreate([
  HTTP_PROVIDERS
]);

this.http = injector.get(Http);

There are several questions here on Stackoverflow with different variants of that same code, but none of them works in RC.5+.

Does anybody know of how to perform that same thing in RC.5+?

回答1:

Just look at the source for HttpModule. You'll see all the providers required to create the Http. Most of those providers were what were in the now removed HTTP_PROVIDERS

export function _createDefaultCookieXSRFStrategy() {
  return new CookieXSRFStrategy();
}

export function httpFactory(xhrBackend: XHRBackend, requestOptions: RequestOptions): Http {
  return new Http(xhrBackend, requestOptions);
}

@NgModule({
  providers: [
    {provide: Http, useFactory: httpFactory, deps: [XHRBackend, RequestOptions]},
    BrowserXhr,
    {provide: RequestOptions, useClass: BaseRequestOptions},
    {provide: ResponseOptions, useClass: BaseResponseOptions},
    XHRBackend,
    {provide: XSRFStrategy, useFactory: _createDefaultCookieXSRFStrategy},
  ],
})
export class HttpModule {
}

Just add everything in the above providers to the array you pass to ReflectiveInjector.resolveAndCreate.

If your goal is to get the Http before bootstrap, there's another little thing you need to take care of, which is the CookieXSRFStrategy. It will not work prior to bootstrapping, as it is dependendent on some platform browser stuff. You can just replace it with a noop, as mentioned in this post

回答2:

Finally found an answer.

You can use Injector to get dependency as shown below.

service.ts

import { Injectable,Injector } from '@angular/core';
import {Http} from '@angular/http';

@Injectable()
export class Service{
    constructor(private injector:Injector){}

    display(){

        this.http=this.injector.get(Http);   //<<<<------here the magic happens

        console.log(this.http);
        return this.http.get('user.json').map(res => {return res.json()}).toPromise();
    } 
}

If you still have any doubt, you can check this working plunker made in Angular2.0.0 :
https://plnkr.co/edit/eWLB2BaL66pnJ7SC6qAL?p=preview