Add an RSS Feed Through a Custom Control

Following the class declaration, four member variables are declared within a declarations region; one for the web service and three string variables used to contain the RSS feed, the user defined RSS Feed Title, and one for the content returned by the web service.

    #Region "Declarations"

         Private mNews As net.webservicex.www.RSStoHTML

         Private mMessage As String

         Private mRssUrl As String

         Private mRssTitle As String

    #End Region

Next up is the methods region which contains the initialization event handler for the RSS control:

#Region "Methods"

    Private Sub RssCC_Init(ByVal sender As Object, ByVal e As System.EventArgs)

    Handles Me.Init

        If Not RssFeed Is String.Empty Then

            mNews = New net.webservicex.www.RSStoHTML

            mMessage = mNews.GetHTML(RssFeed)

        End If

    End Sub

#End Region

The initialization event handler checks to see if the RSS feed property is empty and, if it is not, it evokes the web services Get HTML web method to populate the message member variable with the HTML version of the information returned by the service.

The next region in the project is called “Properties” and it contains the two properties used by the control.  RSS Feed and RSS Feed Title.  The properties update or read from the content of private member variables to manage their content.  The RssFeed property is used to contain the path to the RSS feed while the RssFeedTitle property allows the user to key a title for the control.

#Region "Properties"

    <Category("RSS Feed")> _

    <Browsable(True)> _

    <Description("Enter the URL for the RSS Feed.")> _

    Public Property RssFeed() As String

        Get

            Return mRssUrl

        End Get

        Set(ByVal value As String)

            mRssUrl = value

        End Set

    End Property

    <Category("RSS Feed")> _

    <Browsable(True)> _

    <Description("Enter the title for the RSS Feed.")> _

    Public Property RssFeedTitle() As String

        Get

            Return mRssTitle

        End Get

        Set(ByVal value As String)

            mRssTitle = value

        End Set

    End Property

#End Region

The last detail to tend to is the rendering; here RenderContents is overridden and, within a try – catch block, a set of nested Divs are created.  Within the main Div there are two separate divs, one to hold the user defined title for the feed, and one to display the HTML.  In both instances, the content is rendered by a label control added to the div.  If the rendering operation fails, the control will display “RSS Feed Offline” to the user.

#Region "Rendering"

    Protected Overrides Sub RenderContents(ByVal output As HtmlTextWriter)

        Try

            output.AddAttribute(HtmlTextWriterAttribute.Align, "center")

            output.AddAttribute(HtmlTextWriterAttribute.Valign, "top")

            output.AddAttribute(HtmlTextWriterAttribute.Width, "100%")

            output.RenderBeginTag(HtmlTextWriterTag.Div)

            output.AddAttribute(HtmlTextWriterAttribute.Align, "left")

            output.AddAttribute(HtmlTextWriterAttribute.Valign, "top")

            output.AddAttribute(HtmlTextWriterAttribute.Width, "50%")

            output.RenderBeginTag(HtmlTextWriterTag.Div)

            Dim lbl As New Label

            lbl.ID = "lblRssTitle"

            lbl.Text = "<b>" & Me.RssFeedTitle.ToString() & "</b>"

            lbl.RenderControl(output)

            output.RenderEndTag()

            output.AddAttribute(HtmlTextWriterAttribute.Align, "left")

            output.AddAttribute(HtmlTextWriterAttribute.Valign, "top")

            output.AddAttribute(HtmlTextWriterAttribute.Width, "50%")

            output.RenderBeginTag(HtmlTextWriterTag.Div)

            Dim lbl2 As New Label

            lbl2.ID = "lblRssContent"

            lbl2.Text = mMessage.ToString()

            lbl2.RenderControl(output)

            output.RenderEndTag()

            output.RenderEndTag()

        Catch

            output.RenderBeginTag(HtmlTextWriterTag.Div)

            output.Write("RSS Feed Offline")

            output.RenderEndTag()

        End Try

    End Sub

#End Region

Summary