ERROR TypeError: Cannot read property 'loaded' of undefined

export class UsersComponent implements OnInit {
    loaded:boolean = false;

    ngOnInit() {
        ...
        ...
        this.loaded = true;
    }
}

import { Component, AfterViewInit, ViewChild } from '@angular/core';
import { UsersComponent } from '../events/users.component';

export class RolesComponent implements AfterViewInit {

  @ViewChild(UsersComponent) event;

  constructor() { }

  ngAfterViewInit() {
    console.log(this.event.loaded);
  }

}