更新:

感谢j2L4e的提示！

Thanks to j2L4e, for his hint!

BehaviorSubject是关键！

看到这个矮人:

https://plnkr.co/edit/whkrQk3tHCJCvvi6rlaE?p=info

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

import { Subject, BehaviorSubject } 'rxjs/Rx';
//import { Observable, Subject } from 'rxjs';

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2 (click)="showMe = !showMe">Hello {{name}}</h2>
      <br />

      <div *ngIf="showMe">
        sbj1: {{  _subj1 | async  }}
      </div>

      <div *ngIf="showMe">
        obs1: {{  _obs1 | async  }}
      </div>

      <div *ngIf="showMe">
        obs2: {{  _obs2 | async  }}
      </div>
    </div>
  `,
})
export class App {

  private showMe = false;

  private _subj1 = new BehaviorSubject<string>();
  private _subj2 = new Subject<string>();
  private _obs1 = this._subj1.asObservable();
  private _obs2 = this._subj2.asObservable();

  constructor() {
    this.name = 'Angular2'

    this._subj1.next('in constructor');
  }

  ngAfterViewInit() {
    this._subj2.next('after view init..');
  }
}

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