将数据从服务发送到可观察的 Get 请求 [英] Send data from service to observable Get request

问题描述

我是 Angular 和 Observables 的新手.我有一个服务，它接收一个 URL，我想在每次使用 NgFor 将新 URL 传递给它时传递给我的 observable 并呈现数据.任何例子都会有所帮助.请帮助似乎没有任何效果.提前致谢

I am new to Angular and Observables. I have a service that receives a URL I want to pass to my observable and render data every time a new URL is passed to it with NgFor. Any example would help. Please help nothing seems to work. Thanks in advance

服务文件

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)
}

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);
  }
}

发送组件文件

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

推荐答案

我想我理解你的问题.

http.get(url) 是一个一次性的 observable.它不是可以像主题那样多次触发的流.您需要创建自己的主题并将其用作代理.

The http.get(url) is a single-use observable. It's not a stream that can be triggered multiple times like subjects can. You will need to create your own subject and use that as a proxy.

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 阅读此设计模式的其他解决方案可能会很有用，因为这是一个相当简单的例子.

This is the pub-sub design pattern (publisher - subscriber). It might be useful to read up on other solutions to this design pattern using Angular, as this is a fairly trivial example.

您还需要在完成订阅后取消订阅组件以避免内存泄漏.

You will also want to unsubscribe in your component once you're done with the subscription to avoid memory leaks.

这样的东西是一个简单的模式:

Something like this is a simple pattern:

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();
  }
}

虽然如果你需要开始做很多事情，它确实会重复.我个人使用这种方法:https://stackoverflow.com/a/45709120/5367916

Although it does get repetitive if you need to start doing it a lot. I personally use this method: https://stackoverflow.com/a/45709120/5367916

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