Introduction
This article discusses the construction of a simple application that may be 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 treeview control; each title becomes the parent of the related link.
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.
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:
Figure 3: Solution Explorer.
As you can see, the project is a WinForms application containing only a single form. The form itself contains a toolstrip control docked to the top with a textbox used for entering RSS feed locations, a button control to open the RSS feed, and a combobox containing a collection of RSS feeds which may be directly opened. The left hand side of the form contains a treeview 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; the 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, the class is defined and a constructor added. A local string variable is 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
Private mRssUrl As String
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
mRssUrl = String.Empty
End Sub
Next up is the click event handler for the RSS Go button located on the form’s toolstrip 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 treeview and make it possible for users 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 is annotated and should be easy enough to follow using the comments:
Private Sub tsRssGo_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles
tsRssGo.Click
Try
mRssUrl = Me.tsRssLocation.Text
tvwRss.Nodes.Clear()
Me.Cursor = Cursors.WaitCursor
Dim doc As New XmlDocument()
Try
doc.Load(mRssUrl)
Me.Cursor = Cursors.Default
Catch ex1 As Exception
Me.Cursor = Cursors.Default
MessageBox.Show(ex1.Message)
Return
End Try
Dim navigator As XPathNavigator = doc.CreateNavigator()
Try
Dim nodes As XPathNodeIterator =
navigator.Select("/rss/channel/item/title")
While nodes.MoveNext
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, "")
tvwRss.Nodes.Add(tmp)
End While
Dim position As Integer = 0
Dim nodesLink As XPathNodeIterator =
navigator.Select("/rss/channel/item/link")
While nodesLink.MoveNext
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, "")
tvwRss.Nodes(position).Nodes.Add(tmp)
position += 1
End While
Catch ex As Exception
MessageBox.Show(ex.Message, "RSS Feed Load Error")
End Try
Me.Cursor = Cursors.Default
Catch ex2 As Exception
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 AfterSelect event from the treeview 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.
Private Sub tvwRss_AfterSelect(ByVal sender As System.Object, _
ByVal e As
System.Windows.Forms.TreeViewEventArgs) _
Handles tvwRss.AfterSelect
Try
Dim tmp As String = tvwRss.SelectedNode.Text.Substring(0, 4)
If tmp = "http" Then
webBrowser1.Navigate(tvwRss.SelectedNode.Text)
End If
Catch
End Try
End Sub
The last method in the class is the handler for the canned feeds combobox 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 toolstrip’s RSS Location textbox control and the toolstrip control’s RSS Go button’s click event is fired. That button click event handler will clear the treeview control and reload it with the information captured from the replacement RSS feed.
Private Sub tsCboFeeds_SelectedIndexChanged(ByVal sender _
As System.Object, ByVal e As System.EventArgs) _
Handles tsCboFeeds.SelectedIndexChanged
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 readers 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 treeview 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.
History
- 3rd June, 2008: Initial version
Submit an article or tip
