Angular Material md-icon error No provider for Http

Question

When using <md-icon> I get this error:

ORIGINAL EXCEPTION: No provider for Http!

So I added HTTP_PROVIDERS to my component and it solved it. So my question... Why do I need to add HTTP_PROVIDERS to my component to get <md-icon> to work even though I'm not using HTTP_PROVIDERS in my app otherwise?!

Here's my working component. Removing HTTP_PROVIDERS from the providers array throws the above error.

import { Component } from '@angular/core';
import { HTTP_PROVIDERS } from '@angular/http';
import { MdIcon, MdIconRegistry } from '@angular2-material/icon';

@Component({
  moduleId: module.id,
  selector: 'foo-app',
  template: `<md-icon>face</md-icon>`,
  directives: [ MdIcon ],
  providers: [MdIconRegistry, HTTP_PROVIDERS]
})
export class FooAppComponent {
  title = 'Material 2 Foo App';
}

One other note, this line will display the icon with no Http error and no need for HTTP_PROVIDERS:

<i class="material-icons">face</i>

Answer 1

Angular 7

For me the solution to this error was to add MatIconRegistry to providers on my APP module:

@NgModule({
  declarations: [..],
  imports: [
   ..,MatIconModule,
    HttpClientModule,
   ..
  ],
  providers:[  MatIconRegistry ],
  exports: [..]
})
export class SomeModule { }

Answer 2

Looking into the source code a bit for angular2-material, md-icon depends on angular2's Http which is why you're seeing the need for HTTP_PROVIDERS.

heres a link to the source: https://github.com/angular/material2/blob/master/src/components/icon/icon.ts

in /src/components/icon/icon.ts, the class requires MdIconRegistry with MdIcon having the constructor:

constructor(
  private _element: ElementRef,
  private _renderer: Renderer,
  private _mdIconRegistry: MdIconRegistry) { }

and MdIconRegistry requires Http with MdIconRegistry having the constructor:

  constructor(private _http: Http) {}

I guess Http is used to perhaps get icons from a url? So if you dig a few levels down into the source code, you can find Http in there.