完成后n秒重复请求（Angular2 - http.get） [英] Repeat request (Angular2 - http.get) n seconds after finished

问题描述

我玩了angular2并且在一段时间后陷入困境。

I played around with angular2 and got stuck after a while.

使用 http.get 工作正常一个请求，但我想每4秒轮询一次实时数据，经过一段时间的修补和读取很多反应性的东西我最终得到：

Using http.get works fine for a single request, but I want to poll live-data every 4 seconds, after tinkering for quite a while and reading a lot of reactivex stuff i ended up with:

Observable.timer(0,4000)
  .flatMap(
    () => this._http.get(this._url)
       .share()
       .map(this.extractData)
       .catch(this.handleError)
  )
  .share(); 

是否有简单方式开始（4秒）间隔后 http.get -observable发出了请求的结果？ （或者我最终会在 observable-hell ？）

Is there a simple way to start a (4 second) interval after the http.get-observable has emitted the result of the request? (Or will I end up in observable-hell?)

我想要的时间表：

Time(s): 0 - - - - - 1 - - - - - 2 - - - - - 3 - - - - - 4 - - - - - 5 - - - - - 6
Action:  Request - - Response - - - - - - - - - - - - - - - - - - - -Request-... 
Wait:                | wait for 4 seconds -------------------------> |

推荐答案

更新至RxJS 6

import { timer } from 'rxjs';
import { concatMap, map, expand, catchError } from 'rxjs/operators';

pollData$ = this._http.get(this._url)
  .pipe(
    map(this.extractData),
    catchError(this.handleError)
  );

pollData$.pipe(
  expand(_ => timer(4000).pipe(concatMap(_ => pollData$)))
).subscribe();

---

我正在使用RxJS 5而我是不确定RxJS 4等效运算符是什么。无论如何这里是我的RxJS 5解决方案，希望它有所帮助：

---

I'm using RxJS 5 and I'm not sure what the RxJS 4 equivalent operators are. Anyway here is my RxJS 5 solution, hope it helps:

var pollData = this._http.get(this._url)
            .map(this.extractData)
            .catch(this.handleError);
pollData.expand(
  () => Observable.timer(4000).concatMap(() => pollData)
).subscribe();

扩展运算符将发出数据并以每次发射递归启动一个新的Observable

The expand operator will emit the data and recursively start a new Observable with each emission

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