我的服務import { Injectable } from "@angular/core";import { Observable, of } from "rxjs";import { SearchResult } from "../Components/container-search/Models/SearchResult";import { environment } from "../../environments/environment";import { HttpClient, HttpHeaders } from "@angular/common/http";@Injectable({  providedIn: "root",})export class ContainerService {  constructor(public http: HttpClient) {}  private SearchResults: SearchResult[] = [];  public headers = {    headers: new HttpHeaders({      "Content-Type": "application/json",    }),  };  public Search(): Observable<SearchResult[]> {    if (this.SearchResults.length === 0) {       this.http        .get<SearchResult[]>(          environment.endpointURL + "/FooBar/Search",          this.headers        )        .subscribe((x) => {          this.SearchResults = x;          return of(this.SearchResults);        });    } else {      return of(this.SearchResults);    }  }}當我在我的組件中調用 Search（） 時，它返回TypeError: Cannot read property 'subscribe' of undefined我的通話代碼是  ngOnInit(): void {    this.dataSource.paginator = this.paginator;     this.searchService.Search().subscribe((x) => {      this.dataSource = new MatTableDataSource<SearchResult>(x);    });  }有人可以解釋為什么此代碼總是返回上述錯誤嗎？this.searchService.Search()