RxJS サブジェクトまたはオブザーバブルの現在の値にアクセスするにはどうすればよいですか?

<code class="typescript">private _isLoggedInSource = new BehaviorSubject<boolean>(false);
isLoggedIn = this._isLoggedInSource.asObservable();</code>

<code class="typescript">import { SessionStorage } from './session-storage.service';
import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'my-component',
  templateUrl: './my-component.html'
})
export class MyComponent implements OnInit {

  isLoggedIn: boolean;

  constructor(private sessionStorage: SessionStorage) { }

  ngOnInit() {
    this.isLoggedIn = this.sessionStorage.isLoggedIn.getValue();
  }

}</code>