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How to access RSS feeds from code

.NET ne permite sa accesam feed-uri in format RSS sau ATOM fara nici o problema. XML returnat de un RSS nu trebuie sa il procesam noi manual, exista deja clase in .NET care pot sa faca acest lucru.
In postul de astazi o sa ne vedem cum putem sa incarcam un feed de tip RSS din cod.
Dupa cum stiti, formatul unui feed RSS este XML. Acest format este deja standardizat si nu ar trebui sa ne trezim cu campuri noi. In general un feed RSS contine date despre cine ne furnizeaza aceste date precum titlu, descriere, link, data publicarii, etc. Iar fiecare element( feed) contine: titlu, descriere, id unic( GUID), descriere si data publicarii. Mai jos puteti sa gasiti un exemplu de fisier RSS versiunea 2.0 care contine un singur feed:
<?xml version="1.0" encoding="UTF-8" ?>
<rss version="2.0">
<channel>
<title>RSS Title</title>
<description>This is an example of an RSS feed</description>
<link>http://www.someexamplerssdomain.com/main.html</link>
<lastBuildDate>Mon, 06 Sep 2010 00:01:00 +0000 </lastBuildDate>
<pubDate>Mon, 06 Sep 2009 16:45:00 +0000 </pubDate>
<ttl>1800</ttl>

<item>
<title>Example entry</title>
<description>Here is some text containing an interesting description.</description>
<link>http://www.wikipedia.org/</link>
<guid>unique string per item</guid>
<pubDate>Mon, 06 Sep 2009 16:45:00 +0000 </pubDate>
</item>

</channel>
</rss>
Sursa: http://en.wikipedia.org/wiki/RSS#Example
O varianta simpla de a accesa aceasta informatie, este facem un request spre adresa URL care ne returneaza aceste date, iar apoi folosindu-ne de clasa SyndicationFeed putem sa incarcam si sa accesam aceste date ca si niste feed-uri.
Primul pas este obtinem datele in format XML. Pentru acest lucru putem sa ne folosim de clasa WebClient, prin intermediul careia putem sa obtinem continul returnat de orice adresa URL.
WebClient webClient = new WebClient();
string rssResult = webClient.DownloadString(rssUrl);
Folosind metoda DownloadString, continutul returnat de catre URL dat se va copia local ca si un string. WebClient ne mai permite sa copiem continutul si ca si un sir de bytes( DownloadData) sau sa copiem continutul direct intr-un fisier( DownloadFile). Aceasta actiune se poate face atat sincron cat si asincron.
Pentru a putea accesa aceste resurse, WebClient tine cateva resurse legate de retea blocate. Din aceasta cauza este bine sa facem dispose la instanta unui obiect de tip WebClient, cand nu mai avem nevoie de el.
string rssResult = null;
using(WebClient webClient = new WebClient())
{
rssResult = webClient.DownloadString(rssUrl);
}
Odata ce avem rssResult, putem sa incarcam rezultatul folosindune de SyndicationFeed. Prin intermediul acestei clase putem sa cream noi feed-uri RSS sau ATOM, dar putem sa si incarcam feed-uri RSS deja existente.
SyndicationFeed feed = SyndicationFeed.Load( rssResult );
Din acest moment, folosindu-ne de obiectul feed, putem sa accesam orice date in felul urmator:
feed.Title
feed.Description
feed.Id
Fiecare item poate sa fie gasit sub propietatea Items, care contine o colectie de obiecte de tip SyndicationItem. Fiecare element de acest tip o sa contina date despre "stirea" curenta.
SyndicationItem item = feed.Item.First();
... = item.Title;
... = item.Description;
In acest post am vazut o modalitate prin care putem accesa un RSS feed folosind WebClient si SyndicationFeed.
Enjoy!

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