将数据从服务发送到可观察的Get请求

Question

我是Angular和Observables的新手。我有一个服务，该服务接收要传递给我的可观察对象的URL，并在每次通过NgFor将新URL传递给它时呈现数据。任何示例都会有所帮助。请帮助什么似乎都没有用。在此先感谢

SERVICE文件

import { Injectable } from '@angular/core';
import { HttpClient, HttpErrorResponse, HttpHeaders, HttpParams } from '@angular/common/http';
import { Observable } from 'rxjs';
import { Event } from '../event/event.interface';
import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})

export class ClientService {

  eventUrl ;

  constructor(private http: HttpClient) {
  }

 receiveEvent(eventId){
    this.eventUrl = eventId;
   console.log(this.eventUrl)
 }

renderEvent(eventUrl): Observable<Event[]>{
  return this.http
  .get<Event[]>(eventUrl)
}

正在接收组件文件

import { Component, OnInit, Input, Output, EventEmitter } from '@angular/core';
import { ClientService } from '../service/clientService';
import { HttpParams, HttpClient } from '@angular/common/http';


@Component({
  selector: 'hero-review',
  templateUrl: './review.component.html',
  styleUrls: ['./review.component.css']
})
export class ReviewComponent implements OnInit {

public events = [];

  constructor(private _clientService: ClientService) { 
  }

  ngOnInit() {

    this._clientService.renderEvent('Need to be dynamic URL').subscribe(data => this.events = data);
  }
}

SENDING COMPONENT文件

sendEvent(eventId){
  let reqUrl = "myEndpoint" + eventId;
  this._clientService.receiveEvent(reqUrl);
}

Answer 1

我想我了解您的问题。

http.get（url）是一次性的可观察对象。这不是像主题一样可以多次触发的流。您将需要创建自己的主题并将其用作代理。

export class ClientService {

 constructor(private http: HttpClient) {
 }

 private eventPublisher: Subject<Event[]> = new Subject<Event[]>();

 receiveEvent(eventId){
   // call http client here, and publish results to event publisher
   const eventUrl = eventId;
   this.http.get<Event[]>(eventUrl).subscribe(response => {
     this.eventPublisher.next(response);
   });
 }

 renderEvent(eventUrl): Observable<Event[]>{
  // do not subscribe to http client here, subscribe to event publisher
  return this.eventPublisher.asObservable();
 }

这是发布订阅设计模式（发布者-订阅者）。使用Angular来阅读有关此设计模式的其他解决方案可能会很有用，因为这是一个非常简单的示例。

编辑：

您还需要在完成订阅后取消订阅组件，以避免内存泄漏。

类似这样的简单模式：

export class MyComponent implements OnInit, OnDestroy() {
  constructor(private myService: MyService) { }

  private destroyed: Subject<void> = new Subject<void>();

  ngOnInit(): void {
    this.myService.myMethod().pipe(
      takeUntil(() => this.destroyed)
    ).subscribe(() => { 
      // do stuff
    });
  }

  ngOnDestroy(): void {
    this.destroyed.next(undefined);
    this.destroyed.complete();
  }
}

尽管如果您需要大量开始，它的确会重复。我个人使用此方法：https://stackoverflow.com/a/45709120/5367916