Introduction:

This article discusses the construction of a simple application that may used to view RSS feeds from the desktop. The application allows the user to select a canned RSS feed or to key one. The RSS feed is opened and the article title and link nodes from the feed are placed into a tree view control; each title becomes the parent of the related link.

RSS-Feed-VB.Net.gif

Figure 1: Application in Use

The title of the article occupies the parent node with the link node placed as the child of each title node. If the user clicks on any of the link nodes, the article associated with the title will be opened into a web browser control.

RSS-Feed-Speed-Vb.net.gif

Figure 2: Canned RSS Feeds in drop down, current RSS feed on left side

The intent of the application was to provide a simple tool that may be used to organize and read RSS postings. The titles and links are recovered from the XML returned from the RSS service.

Getting Started:

In order to get started, unzip the included project and open the solution in the Visual Studio 2008 environment. In the solution explorer, you should see this:

Solution-Explorer-Vb.net.gif

Figure 3: Solution Explorer

As you can see, the project is a win forms application containing only a single form. The form itself contains a tool strip control docked to the top with a text box used for entering RSS feed locations, a button control to open the RSS feed, and a combo box containing a collection of RSS feed which may be directly opened. The left hand side of the form contains a tree view control used to display the RSS feed titles and links; the right hand side contains a web browser control which is used to display the linked page.

The Main Form (frmRss.vb).

The main form is used to open the selected RSS feed as an XML document and to display them in TreeView format; form also places the story link as a child node to each title node.

If you'd care to open the code view up in the IDE you will see that the code file begins as follows:

Imports System.Xml

Imports System.Xml.XPath


 Note that the additions of the System.Xml and System.Xml.XPath libraries are the only actual departure from the default. Following the imports, class is defined and a constructor added. A local string variable it declared and used to hold the RSS feed URL. Within the constructor, the string variable used to point to the location of the RSS feed is zeroized as an empty string.

Public Class frmRss

' Current Path to RSS Feed

Private mRssUrl As String

''' <summary>

''' Set the RSS URL to an empty

''' string on form load

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub Form1_Load(ByVal sender As System.Object, _ByVal e As System.EventArgs)Handles MyBase.Load

' Clear path to RSS Feed

mRssUrl = String.Empty

End Sub


 Next up is the click event handler for the RSS Go button located on the form's tool strip control.Within this click event handler, the code is placed to query for only the RSS feed item title and link.These two values are loaded into the tree view and make it possible for the user to read the article title and then open the link into the web browser control to read it if they are interested in getting more information on the topic. This section of code in annotated and should be easy enough to follow using the comments:

''' <summary>

''' Pull up an RSS feed and load its headlines

''' and links into a treeview control

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub tsRssGo_Click(ByVal sender As System.Object, _ByVal e As System.EventArgs)Handles tsRssGo.Click

Try

' set the file path member var

mRssUrl = Me.tsRssLocation.Text

' Clear the treeview.

tvwRss.Nodes.Clear()

' set the wait cursor

Me.Cursor = Cursors.WaitCursor

' create a new xml doc

Dim doc As New XmlDocument()

Try

' load the xml doc

doc.Load(mRssUrl)

' return the cursor

Me.Cursor = Cursors.Default

Catch ex1 As Exception

' return the cursor

Me.Cursor = Cursors.Default

' tell a story

MessageBox.Show(ex1.Message)

Return

End Try

' get an xpath navigator

Dim navigator As XPathNavigator = doc.CreateNavigator()

Try

' look for the path to the rss item titles navigate

' through the nodes to get all titles

Dim nodes As XPathNodeIterator =

navigator.Select("/rss/channel/item/title")

While nodes.MoveNext

' clean up the text for display

Dim node As XPathNavigator = nodes.Current

Dim tmp As String = node.Value.Trim()

tmp = tmp.Replace(ControlChars.CrLf, "")

tmp = tmp.Replace(ControlChars.Lf, "")

tmp = tmp.Replace(ControlChars.Cr, "")

tmp = tmp.Replace(ControlChars.FormFeed, "")

tmp = tmp.Replace(ControlChars.NewLine, "")

' add a new treeview node for this

' news item title

tvwRss.Nodes.Add(tmp)

End While

' set a position counter

Dim position As Integer = 0

' Get the links from the RSS feed

Dim nodesLink As XPathNodeIterator =

navigator.Select("/rss/channel/item/link")

While nodesLink.MoveNext

' clean up the link

Dim node As XPathNavigator = nodesLink.Current

Dim tmp As String = node.Value.Trim()

tmp = tmp.Replace(ControlChars.CrLf, "")

tmp = tmp.Replace(ControlChars.Lf, "")

tmp = tmp.Replace(ControlChars.Cr, "")

tmp = tmp.Replace(ControlChars.FormFeed, "")

tmp = tmp.Replace(ControlChars.NewLine, "")

' use the position counter

' to add a link child node

' to each news item title

tvwRss.Nodes(position).Nodes.Add(tmp)

' increment the position counter

position += 1

End While

Catch ex As Exception

MessageBox.Show(ex.Message, "RSS Feed Load Error")

End Try

' restore the cursor

Me.Cursor = Cursors.Default

Catch ex2 As Exception

' snitch

MessageBox.Show(ex2.ToString(), "RSS Feed Initialization

Failure")

End Try

End Sub

 The next section of the code is used to load the link content into the web browser control. This is accomplished using the After Select event from the tree view control. When this event fires, the code merely examines the link text and, if it starts with 'http'; the function makes an attempt to load the link into the web browser control occupying the right hand panel in the main form.

''' <summary>

''' Upon selection of a node, open the link

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub tvwRss_AfterSelect(ByVal sender As System.Object, _ ByVal eAs System.Windows.Forms.TreeViewEventArgs) _ Handles tvwRss.AfterSelect

Try

' get the first four characters from the link for a

' quick test

Dim tmp As String = tvwRss.SelectedNode.Text.Substring(0, 4)

' test the link text and then

' navigate the browser to that link

If tmp = "http" Then

webBrowser1.Navigate(tvwRss.SelectedNode.Text)

End If

Catch

' skip it if it isn't a link

End Try

End Sub

The last method in the class is the handler for the canned feeds combo box selected index changed event; in this code, when the user selects a canned feed from the drop down list, that link is loaded into the tool strip's RSS Location text box control and the tool strip control's Rss Go button's click event is fired. That button click event handler will clear the tree view control and reload it with the information captured from the replacement RSS feed.

''' <summary>

''' Load the selected canned RSS feed into the

''' treeview using the existing methods

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub tsCboFeeds_SelectedIndexChanged(ByVal sender _As System.Object, ByVal e AsSystem.EventArgs) _ Handles tsCboFeeds.SelectedIndexChanged

' load the text for the selected feed into

' the RSS location text box and then use

' the existing button click event to launch

' the RSS feed into the treeview

tsRssLocation.Text = tsCboFeeds.SelectedItem.ToString()

tsRssGo_Click(Me, New EventArgs())

End Sub

End Class


 Summary
This application demonstrates a simple way of building an RSS Feed reader through the manipulation of the RSS Feed's XML. This is a little different than most of the RSS Feeder reader's I have encountered in that it does not attempt to provide the standard set of information returned from the feed in a listbox or similar control; rather this approach only displays the headlines and provides the links to the main story using the tree view control and a web browser control; in that the user can scan the headlines and then pop open the link directly to display the main story in a web browser control. Of course you can pull addition information from the feed and display it using other added controls; the approach is certainly something that can be expanded upon; however this does provide a clean and simple interface to the RSS Feeds main points of information.