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Contents of this writing:
- Version History
- Sample; RSS Bars Library
- Further Readings
This writing does not include a full discussion or even the full details of RSS or XML. Rather, it includes a nice introduction to RSS and its XML schema. In addition, it incorporates what you get in a sample application that is easy-to-code, understand, and to extend.
RSS (commonly expanded as Really Simple Syndication or, sometimes, Rich Site Summary) is a XML content with specific schema used to deliver frequently changing web content (like news headlines, blogs, etc.).
RSS content is also known as a feed, web feed, syndication feed, web syndication, and a channel. It is widely known and distinguished by its icon €œ€.
RSS feeds are usually files that reside in a specific location. Those files usually (not extensively) has the extension rss or xml.
Today, most -if not all – of the blogs and sites that have frequently changing web content incorporate RSS.
For instance, The New York Times has more than one hundred of RSS feeds available for subscription (listed here.) Every feed delivers the latest headlines for a specific category (Technology, Sports, etc.)
How can you benefits from RSS feeds? Surely, XML data is not the flexible and readable content that can be used. Thus, users usually access feeds via applications (or web clients) that are known as Feed Readers, RSS Readers, and Aggregators. Those applications read the RSS XML content, parse it, and display feed items (e.g. news headlines) to the user in a friendly interface.
RSS undergoes several changes that result in different versions and two major branches:
- RDF (Resource Description Framework) or RSS 1.* in other words.
- RSS 2.*
We will assume RSS 2.* is our discussion.
As any other XML format, RSS has a specific schema that RSS contents (i.e. feeds) should comply with; they required to implement obligatory elements, and they had the choice to implement other optional elements.
As a matter of discussion, we will take the CodeProject latest articles RSS feed (available here) as an example and extract the RSS schema from it.
The following is a sample from the CodeProject RSS feed content (at the time of this writing):
<?xml version="1.0" encoding="utf-8"?> <rss xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" version="2.0"> <channel> <title>The Code Project Latest Articles</title> <link>http://www.codeproject.com</link> <description>Latest Articles from The Code Project</description> <language>en-us</language> <image> <title>The Code Project</title> <url>http://www.codeproject.com/images/codeproject100x30.gif</url> <link>http://www.codeproject.com</link> <width>100</width> <height>30</height> <description>The Code Project</description> </image> <copyright>Copyright &copy; CodeProject, 1999-2010</copyright> <webMaster>firstname.lastname@example.org</webMaster> <lastBuildDate>Sun, 04 Apr 2010 12:27:00 GMT</lastBuildDate> <ttl>20</ttl> <generator>C# Hand-coded goodness</generator> <item xsi:type="article"> <title>Comparison of Architecture presentation patterns MVP(SC),MVP(PV), ...</title> <description>This article will compare four important architecture ...</description> <link>http://www.codeproject.com/KB/aspnet/ArchitectureComparison.aspx</link> <author>Shivprasad koirala</author> <pubDate>Sun, 04 Apr 2010 12:27:00 GMT</pubDate> <subject>ASP.NET</subject> <GUID>http://www.codeproject.com/KB/aspnet/ArchitectureComparison.aspx</GUID> </item> <item xsi:type="article"> <title>Arcade Button in Expression Blend & Silverlight</title> <description>Discover the power of the Grid object, & how it controls ...</description> <link>http://www.codeproject.com/KB/expression/ArcadeButton.aspx</link> <author>Alan Beasley</author> <pubDate>Sun, 04 Apr 2010 11:42:00 GMT</pubDate> <subject>Expression</subject> <GUID>http://www.codeproject.com/KB/expression/ArcadeButton.aspx</GUID> </item> <item xsi:type="article"> <title>How to translate your forms application</title> <description>Translate your forms application to multiple languages ...</description> <link>http://www.codeproject.com/KB/dotnet/forms-translator.aspx</link> <author>Davide Vitelaru</author> <pubDate>Sun, 04 Apr 2010 07:19:00 GMT</pubDate> <subject>.NET Framework</subject> <GUID>http://www.codeproject.com/KB/dotnet/forms-translator.aspx</GUID> </item> </channel> </rss>
If we have a look at the file in XML Notepad we can see the following results:
To gain more understanding of the schema, let’s have a look at this diagram:
Required elements surrounded by the red border. Many other optional elements are available.
Most elements are self-explanatory from their names. However, the following maybe need more explanation:
Content language (e.g. en-us for English for United States.)
The date of the last change of the content.
Time to Live. The number of minutes that indicate how long a channel can be cached before refreshing from the source. You would ignore this element, in many cases.
The name of the program used to generate this feed.
A Globally Unique Identifier used to identify this feed item.
Sample; RSS Bars Library
Our sample project is not an application in itself. Actually it is a WinForms control library that is called Geming.WinForms.RssBars. This library includes bars that read RSS content from a specific feeds and display it to the user.
This is an extensible library you can extend it to read from any RSS feed you like. The following are snapshots of the RssBars controls (reading CodeProject, Just Like a Magic, BBC, and the Nile News channels.)
The following figure shows library class diagram:
As you see, we have only one business object, RssItem structure. It encapsulates fields related to a feed item.
The RssBar is the base MustInherit (abstract in C#) class. It defines the base functionality of a RSS bar. All other classes are just children of the base class. They incorporate the functionality of RssBar by just setting its RSS feed path.
The RssBar requires two parameters for instantiation, the RSS path, and the banner image. For the sake of performance, we have required the developer to pass a banner image of the feed instead of automatically loading it from the image element of the feed content.
To avoid duplication, members of the RssBar are documented in the code.
The core function of the RssBar is the ReadRss() function. This function accesses the RSS feed and populates the list of feed items and display them to the user.
Since RSS is a XML format, we will need to reference the System.Xml.dll library as it is the core library for accessing XML via .NET. (Do not forget to import the System.Xml namespace.)
The following is a sample from the function code. Code abbreviated for clarity.
Public Sub ReadRss() ' Checking design mode, exit if True ' Preparing the screen ' The XML Document Dim xmlDoc As New Xml.XmlDocument ' Loading the RSS feed, should fail if network is not available xmlDoc.Load(m_rss) ' Accessing the €œchannel€ element Dim ndChannel As Xml.XmlNode = xmlDoc.Item("rss").Item("channel") ' Comparing publication date to one we have ' continue if something new ' Item cocollection Dim collItems As New Collections.Generic.List(Of RssItem) Dim ndItem As Xml.XmlNode ' Enumerating through the items ' and populating the collection For i As Integer = 0 To ndChannel.ChildNodes.Count - 1 ndItem = ndChannel.ChildNodes(i) If (ndItem.Name = "item") Then collItems.Add( _ NewRssItem(ndItem.Item("title").ChildNodes(0).InnerText, _ ndItem.Item("link").ChildNodes(0).InnerText, _ ndItem.Item("description").ChildNodes(0).InnerText)) End If Next ' Checking if items cound ' Clear existing items Do While enumerator.MoveNext ' Item lbl = New Label ' Creating a Label for the item ' and filling its fields Me.CtrlsPanel.Controls.Add(lbl) ' Adding handlers, so we could fire events AddHandler lbl.Click, AddressOf Me.RssItem_Click AddHandler lbl.MouseMove, AddressOf Me.RssItem_MouseMove ' Image image = New PictureBox ' Adding the banner image between items Me.CtrlsPanel.Controls.Add(image) ' Adding event handlers, so we could fire events AddHandler image.Click, AddressOf Image_Click AddHandler image.MouseMove, AddressOf Image_MouseMove Loop ' Finalization End Sub
Child classes simply do not contain any code, just the line that instantiates the base RssBar and sets the RSS feed path and image. For instance,Public Sub New() MyBase.New("http://www.codeproject.com/webservices/articlerss.aspx?cat=1", m_image) Me.RightToLeft = Windows.Forms.RightToLeft.No End Sub
Need more about RSS? Here are a few good references:
- XML.com: What Is RSS
- RSS – Wikipedia
- RSS 2.0 Specification (RSS 2.0 at Harvard Low)
- RSS 2.0 Schema
- XML Schema for RSS v2.0
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