Is it possible to use HostListener in a Service?

问题:

I want to create a service which detects all keyboard input, translates the key strokes into actions based on a configurable mapping, and exposes observables which various elements can bind to to react to specific key presses.

The following is a simplification of my code so far, it worked when HostListener was in a component, but now I've moved it into a service it never fires even though it is definitely initialised. Is it not possible to detect input like this in a service?

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

import { Subject } from 'rxjs/Subject';

@Injectable()
export class InputService {

    @HostListener('window:keydown', ['$event'])
    keyboardInput(event: any) {
        console.log(event);
    }
}

回答1:

Seems like its not possible to use it in a service.

You have to use the old way window.addEventListener like @yurzui pointed already.

https://plnkr.co/edit/tc53cvQDfLHhaR68ilKr?p=preview

import {Component, NgModule, HostListener, Injectable} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'

@Injectable()
export class MyService {

  constructor() {
    window.addEventListener('keydown', (event) => {
      console.dir(event);
    });
  }

}

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>Hello {{name}}</h2>
    </div>
  `,
})
export class App {

  constructor(private _srvc: MyService) {
    this.name = 'Angular2'
  }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App ],
  providers: [MyService],
  bootstrap: [ App ]
})
export class AppModule {}