Fetch the Latest xml (url) in WinForm C#

Question

I was just creating a simple internal feedback (RSS) reader (using XML) for intranet; I started by using ListView and populated it with XmlTextReader & XmlDocument.

But this reader is not useful unless I introduce a feature for auto refreshing my reader as soon as the source xml file is updated. One way I could think is:

Fetch the complete file, then compare number of prev/new ChildNodes; if new > prev then load/refresh the Winform. But hundreds of client forms sending these un-important requests will make a joke of the network server's response-time!

I feel I should use some logic to compare Date & Time of creation/update of the XML file. But I've never used such function till today... what do you say, any better idea?

help required regarding the DateTime function, & how to compare them if the file on intranet url is updated. — gsvirdi, May 17 '12 at 07:42
I started by using ListView (in my Windows Forms) and populated it with XmlTextReader & XmlDocument with C Sharp `rssReader = new XmlTextReader(RssFile.ToString()); rssDoc = new XmlDocument(); // Load the XML content into a XmlDocument rssDoc.Load(rssReader);` and RssFile is fetched from `http://111.111.11.11/1.xml` location — gsvirdi, May 17 '12 at 07:52
check this question, there are some useful ideas to improve your polling algorithm http://stackoverflow.com/questions/939642/policy-for-polling-rss — Ventsyslav Raikov, May 17 '12 at 07:52
@Bond Thx a lot for the link, but unfortunately I'm just a beginner and this is a kind of 1st project to understand the network... which means I'm not well educated to understand these advance points. Maybe I will need to get some code to understand what they mean. Btw I'm using windows forms and so I'm not able to understand if I can do anything about using http cache/headers etc in my project. I'm just trying to read a xml file as/when it is updated on the serverr. In the meanwhile I'm consulting google regarding those pooling algo things to know more about them... Thx again :) — gsvirdi, May 17 '12 at 08:04

score 0 · Answer 1 · answered May 19 '12 at 18:06

You can fetch this file like this:

private string fetchRSS(string url, DateTime lastUpdate){
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    request.IfModifiedSince = lastUpdate;
    // if the file wasn't modified since the specified time it won't be fetched and an exception will be thrown
    try{
       WebResponse response = request.GetResponse();

       Stream stream = response.GetResponseStream();
       StreamReader reader = new StreamReader(stream);
       return reader.ReadToEnd();
    }
    // this will happen if the fetching of the file failed or the file wasn't updated
    return null;
}

then when you want to parse the XML do the following:

DateTime lastUpdated = ... // here set the time of the last update
string xmlContent = fetchRSS("http://111.111.11.11/1.xml", lastUpdated);
if(xmlContent != null){
    rssDoc = new XmlDocument();
    // Load the XML content into a XmlDocument
    rssDoc.LoadXml(xmlContent);
}

Fetch the Latest xml (url) in WinForm C#

1 Answers1