使用distinctUntilChanged()方法过滤掉重复数据。

示例代码：

service.ts

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

@Injectable({
  providedIn: 'root'
})
export class DataService {
  private itemsSubject = new BehaviorSubject([]);
  items$ = this.itemsSubject.asObservable();

  addItem(item: string) {
    const currentItems = this.itemsSubject.getValue();
    currentItems.push(item);
    this.itemsSubject.next(currentItems);
  }
}

component.ts

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

@Component({
  selector: 'app-component',
  template: `
    

      {{ item }}
    
  `
})
export class MyComponent implements OnInit {
  items$: Observable;

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.items$ = this.dataService.items$.pipe(distinctUntilChanged());
  }

  addItem(item: string) {
    this.dataService.addItem(item);
  }
}