仅当使用Rx + WebRequest + XDocument.Load进行修改时才检索XDocument [英] Retrieve XDocument only when modified using Rx + WebRequest + XDocument.Load

问题描述

我有以下两个观察值

System.Net.WebRequest req = System.Net.HttpWebRequest.Create("http://test.com/data.xml"); req.Method = "HEAD";

System.Net.WebRequest req = System.Net.HttpWebRequest.Create("http://test.com/data.xml"); req.Method = "HEAD";

var ob = Observable.FromAsyncPattern(req.BeginGetResponse, req.EndGetResponse);

var ob = Observable.FromAsyncPattern(req.BeginGetResponse, req.EndGetResponse);

ob().Select(x => x).Select(x => x.Headers["Last-Modified"]).DistinctUntilChanged(x => x);

ob().Select(x => x).Select(x => x.Headers["Last-Modified"]).DistinctUntilChanged(x => x);

Observable .Interval(TimeSpan.FromSeconds(1.0)) .Select(_ => XDocument.Load("http://test.com/data.xml"));

Observable .Interval(TimeSpan.FromSeconds(1.0)) .Select(_ => XDocument.Load("http://test.com/data.xml"));

我希望XDocument observable仅在最后修改的"标头大于先前请求的文档的任何想法时才执行?

I would like it that the XDocument observable is only executed when "last-modified" header is greater then the previously requested document any ideas?

推荐答案

首先.Select(x => x)是空操作，因此您可以删除它.

Firstly .Select(x=>x) is a no-op so you can remove that.

我会稍微修改一下代码.首先，让我们将其分解为各个组成部分:

I would change the code up a little bit. First lets break it down into its constituent parts:

1)计时器.每秒轮询一次服务器.

1) The Timer. Every second poll the server.

var poll = Observable.Interval(TimeSpan.FromSeconds(1));

var poll = Observable.Interval(TimeSpan.FromSeconds(1));

2)调用获取标头

var lastModified = Observable.FromAsyncPattern(req.BeginGetResponse，req.EndGetResponse).Select(x => x.Headers ["Last-Modified"]);

var lastModified = Observable.FromAsyncPattern(req.BeginGetResponse, req.EndGetResponse).Select(x => x.Headers["Last-Modified"]);

3)选择获取文档

.Select(_ => XDocument.Load("http://test.com/data.xml"));

.Select(_ => XDocument.Load("http://test.com/data.xml"));

我们应该能够很好地构成:

We should be able to compose that nicely:

var lastModified = from interval in Observable.Interval(TimeSpan.FromSeconds(1))
           from response in Observable.FromAsyncPattern(req.BeginGetResponse, req.EndGetResponse)
           select response.Headers["Last-Modified"];

var data = lastModified.DistinctUntilChanged().Select(_ => XDocument.Load("http://test.com/data.xml"));

data.Subscribe(dataXml=> 
   {
       Console.WriteLine("Data has changed!");
       Console.WriteLine(datXml);
   });

Cavet我只是直接在浏览器中输入了.如果编译的话我会很棒.

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