Angular 2`无法读取未定义的属性'dataService‘`

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-example',
  template: '...',
})
export class ExampleComponent {
  constructor(private dataService: DataService) {}
}

import { Injectable } from '@angular/core';

@Injectable()
export class DataService {
  data: any; // 定义data属性

  constructor() {
    this.data = {}; // 初始化data属性
  }

  // 其他方法...
}

import { Component, OnInit } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-example',
  template: '...',
})
export class ExampleComponent implements OnInit {
  data: any;

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.loadData();
  }

  async loadData() {
    this.data = await this.dataService.getData();
  }
}