使用RxJS和angular 2 HTTP服务重新连接服务器

Question

使用RxJS和Angular 2处理服务器重新连接的最佳方法是什么？

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';

import { Observable } from 'rxjs/Observable';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
import 'rxjs/add/operator/takeUntil';
import 'rxjs/add/observable/throw';

@Injectable()
export class ConnectionService {

  // Stores the current status of the connection, false = not connected
  serviceOnline: BehaviorSubject<boolean> = new BehaviorSubject(false)

  constructor(
    private http: Http
  ) {
    this.serviceOnline.asObservable().subscribe((online) => {
      console.log("Service online: " + JSON.stringify(online))
    })
    setTimeout( () => this.setServiceOffline(), 2000 );
  }

  setServiceOffline() {
    console.log("Setting service offline");
    this.serviceOnline.next(false);
    this.testConnection().delay(2000).repeat().takeUntil(this.serviceOnline).subscribe();
  }

  testConnection(): Observable<boolean> {
    console.log("Testing connection");
    return new Observable(observer => {
      this.http.get(`http://endpoint/ping`)
        .timeout(5000)
        .catch((error: any) => Observable.throw(error))
        .subscribe(() => {
          console.log("Connection successful");
          if(this.serviceOnline.getValue() == false)
            this.serviceOnline.next(true);
          observer.next(true);
          observer.complete();
        }, (error) => {
          console.log("Connection failed");
          if(this.serviceOnline.getValue() == true)
            this.serviceOnline.next(false);
          observer.next(false);
          observer.complete();
        });
    })
  }
}

控制台中的结果：

Service online: false
Setting service offline
Service online: false
Testing connection
Connection failed

如果我把这行替换掉..

this.testConnection().delay(2000).repeat().takeUntil(this.serviceOnline).subscribe();

与

this.testConnection().delay(2000).repeat().take(5).subscribe();

Service online: false
Setting service offline
Service online: false
Testing connection
Connection failed
Connection failed
Connection failed
Connection failed
Connection failed

this.serviceOnline.next(false);

...ServiceOnline仅在http服务返回成功响应且当前联机状态为false（断开连接）时发出另一个值：

if(this.serviceOnline.getValue() == false)
   this.serviceOnline.next(true);

所以TakeTaile应该有效。我在这里误解/遗漏了什么？

我是RxJS的新手--任何关于改进这段代码中实现的其他指针也将非常感谢...

Answer 1

我认为出现问题是因为This.ServiceOnline总是在订阅时发出最后一个值，因为它是BehaviorSubject的实例。当您将它作为可观察的通知符传递给TakeTakeTake运算符时，TakeTakeTake将订阅它，并立即接收一个通知，该通知将立即完成结果的可观察性。请注意，无论通知符observable是发出true还是发出false，take，直到completes。

尝试.TakeIte(this.serviceOnline.filter(online=>online===true))。