无法使用ionic 2中的一个订阅函数订阅数据

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

import { HttpClient } from '@angular/common/http';

constructor(private http: HttpClient) {}

getData(): Observable<any> {
  return this.http.get('https://example.com/api/data');
}

subscribeToData() {
  this.getData().subscribe(data => {
    // 在这里处理数据变化的操作
  });
}

import { Component, OnInit } from '@angular/core';

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

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.dataService.getData().subscribe(data => {
      // 在这里处理数据变化的操作
    });
  }

}