Observable and subscriber not working

I can’t understand what I’m doing wrong here? this is my contructor

constructor(public navCtrl: NavController, 
          private dateService: DateService,
          private _emit:EmitterService) {
_emit.navItem$.subscribe(item => {
        this.formattedDate = this.formatDateView(this.dateService.getDate());

this.changeDate = function(type: String): void {

and this is the service which emits

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

export class EmitterService {
  // Observable navItem source
  private _navItemSource = new Subject<Object>();
  // Observable navItem stream
  navItem$ = this._navItemSource.asObservable();
  // service command
  changeNav(item: Object): void {

I console and checked that changeNav is being called but it does not get subscribed

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