如何在angular2中检索可观察变量中的项目总数

import { Component } from '@angular/core';
import { Observable, of } from 'rxjs';
import { scan } from 'rxjs/operators';

@Component({
  selector: 'app-root',
  template: `
    <div>项目总数: {{ itemTotal$ | async }}</div>
  `
})
export class AppComponent {
  // 假设这是一个返回项目数组的可观察对象
  private items$: Observable<any[]> = of([
    { id: 1, name: 'Item 1' },
    { id: 2, name: 'Item 2' },
    { id: 3, name: 'Item 3' }
  ]);

  // 使用scan操作符来累积项目数量
  itemTotal$: Observable<number> = this.items$.pipe(
    scan((acc, items) => acc + items.length, 0)
  );
}

import { Component } from '@angular/core';
import { Observable, of } from 'rxjs';
import { reduce } from 'rxjs/operators';

@Component({
  selector: 'app-root',
  template: `
    <div>项目总数: {{ itemTotal$ | async }}</div>
  `
})
export class AppComponent {
  private items$: Observable<any[]> = of([
    { id: 1, name: 'Item 1' },
    { id: 2, name: 'Item 2' },
    { id: 3, name: 'Item 3' }
  ]);

  // 使用reduce操作符在可观察序列完成时得到总数
  itemTotal$: Observable<number> = this.items$.pipe(
    reduce((acc, items) => acc + items.length, 0)
  );
}