如何在父组件中自动更新服务文件中的变量更改？

import { DataService } from './data.service';

@Component({
  selector: 'app-parent',
  templateUrl: './parent.component.html',
  styleUrls: ['./parent.component.css']
})
export class ParentComponent implements OnInit {
  constructor(private dataService: DataService) { }

  ngOnInit() {
    // 在这里订阅服务中的变量
    this.dataService.variable.subscribe((value) => {
      // 当变量发生变化时，执行相应的操作
      console.log('变量已更新:', value);
    });
  }
}

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

@Injectable({
  providedIn: 'root'
})
export class DataService {
  private variableSource = new BehaviorSubject<string>('初始值');
  variable = this.variableSource.asObservable();

  constructor() { }

  updateVariable(newValue: string) {
    this.variableSource.next(newValue);
  }
}

export class ParentComponent implements OnInit {
  constructor(private dataService: DataService) { }

  updateValue() {
    this.dataService.updateVariable('新的值');
  }
}