使用RxJS Observables来处理异步操作。在第一个方法中使用Observable在关键点发出通知，接着订阅该通知，以等待该方法完成后运行第二个方法。以下是一个示例代码：

import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';

export class ExampleComponent {
  private notification: Subject = new Subject();

  firstMethod(): void {
    // Async operation
    this.notification.next();
  }

  secondMethod(): void {
    // Code to run after firstMethod is done
  }

  ngOnInit() {
    // Subscribe to notification and run second method when it is received
    this.notification.subscribe(() => {
      this.secondMethod();
    });
  }
}