我已经创建了一个方法getProducts，但无法订阅响应，并获得以下错误。

Property 'subscribe' does not exist on type '() => Observable<any>'

服务档桉

public cartItemList :any = [];
   public productsList  = new BehaviorSubject<any>([])
   constructor() { }
   
   getProducts(){
      return this.productsList.asObservable;
   }

组件.ts文件

public totalItem:Number = 0;
  constructor(private cartService:CartService){}
  ngOnInit():void{
    this.cartService.getProducts()
    .subscribe((res:any)=>{
      this.totalItem =res.length;})
  }