在 Angular 中，您可以使用UIService通过BehaviorSubject实现共享状态信息。如果您有两个组件需要这些信息，您可能认为需要在每个组件中订阅一次BehaviorSubject。这将导致重复订阅并可能导致意外的行为。

为了避免重复订阅，可以在UIService中创建一个公共Observable，然后在每个组件中订阅该Observable。这将确保每个组件只订阅一次，并且避免重复订阅。以下是相应的示例代码：

UIService：

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

@Injectable()
export class UIService {
  private readonly _loading = new BehaviorSubject(false);

  readonly loading$ = this._loading.asObservable();

  set loading(value: boolean) {
    this._loading.next(value);
  }
}

Component 1：

import { Component, OnDestroy } from '@angular/core';
import { Subscription } from 'rxjs/Subscription';
import { UIService } from '../ui.service';

@Component({...})
export class MyComponent1 implements OnDestroy {
  private subscription = new Subscription();

  loading: boolean;

  constructor(private uiService: UIService) {
    this.subscription.add(
      uiService.loading$.subscribe(value => (this.loading = value))
    );
  }

  ngOnDestroy() {
    this.subscription.unsubscribe();
  }
}

Component 2：

import { Component, OnDestroy } from '@angular/core';
import { Subscription } from 'rxjs/Subscription';
import { UIService } from '../ui.service';

@Component({...})
export class MyComponent2 implements OnDestroy {
  private subscription = new Subscription();

  loading: boolean;

  constructor(private uiService: UIService) {
    this.subscription.add(
      uiService.loading$.subscribe(value => (this.loading = value))
    );
  }

  ngOnDestroy() {
    this.subscription.unsubscribe();
  }
}

现在，在UI服务中创建了名为“ loading$ ”的共享Observable，每个组件只需