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How can I impliment substring() filter in asp.net XML RSS feed?

Posted on 2009-05-13
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Last Modified: 2012-05-06
I'm having a trouble with substring() filter used in this vb XML RSS feed which I've set up, following a tutorial via this site:
http://www.vbasic.net/detail.aspx?tid=142

The line in the code below which is giving me trouble is, line 40:
objX.WriteElementString("description", dr("NewsStory").ToString.Substring(0, 100) & "..")

The error it produces is:
System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.
Parameter name: length


When I change the description to show the whole News Story, like so:
objX.WriteElementString("description", dr("NewsStory"))

It works perfectly - however isn't the desired/required result.

If you could solve this I would be most grateful.

Cheers!
Imports System.Xml

Imports System.Text

Imports System.Data

Imports System.Data.SqlClient
 

Partial Class newsFeed

    Inherits System.Web.UI.Page
 
 

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
 

        Response.Clear()

        Response.ContentType = "application/rss+xml"

        Dim objX As New XmlTextWriter(Response.OutputStream, Encoding.UTF8)

        objX.WriteStartDocument()

        objX.WriteStartElement("rss")

        objX.WriteAttributeString("version", "2.0")

        objX.WriteStartElement("channel")
 

        Dim cmd As New SqlCommand("Select top 10 * From aspnet_News ORDER BY NewsId DESC", New SqlConnection(ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString))

        cmd.Connection.Open()

        Dim dr As SqlDataReader = cmd.ExecuteReader()
 

        objX.WriteElementString("title", "RSS News Feed")

        objX.WriteElementString("link", "http://www.site.com/news.aspx")

        objX.WriteElementString("description", "The latest news and information from the www.site.com")

        objX.WriteElementString("language", "en-us")

        objX.WriteElementString("ttl", "60")

        objX.WriteElementString("image", "http://www.site.com/Resources/images/logo.gif")

        objX.WriteElementString("lastBuildDate", String.Format("{0:R}", DateTime.Now))
 

        Do While dr.Read()

            objX.WriteStartElement("item")

            objX.WriteElementString("title", dr("NewsTitle").ToString())

            objX.WriteElementString("author", "Name of Author")

            objX.WriteElementString("link", "http://www.site.com/news.aspx?id=" & dr("NewsId"))

            objX.WriteStartElement("guid")

            objX.WriteAttributeString("isPermaLink", "true")

            objX.WriteString("http://www.site.com/news.aspx?id=" & dr("NewsId"))

            objX.WriteEndElement()

            objX.WriteElementString("pubDate", String.Format("{0:R}", dr("NewsDateTime")))

            objX.WriteStartElement("category")

            objX.WriteString(dr("NewsTitle").ToString())

            objX.WriteEndElement()

            'objX.WriteElementString("description", dr("NewsStory")) '//THIS WORKS!

            objX.WriteElementString("description", dr("NewsStory").ToString.Substring(0, 100) & "..") '//THIS DOESNT

            objX.WriteEndElement()

        Loop
 

        objX.WriteEndElement()

        objX.WriteEndElement()

        objX.WriteEndDocument()

        objX.Flush()

        objX.Close()

        Response.End()
 

    End Sub
 

End Class

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Question by:badstyle
  • 4
  • 2
7 Comments
 
LVL 6

Expert Comment

by:ViceroyFizzlebottom
ID: 24379336
You need to ensure that the substring you're asking for isn't longer than the columns data. So you could use:
objX.WriteElementString("description", dr("NewsStory").ToString.Substring(0, dr("NewsStory").Length - 1) & "..")

Simply asking for string data from 0 - 100 will throw an exception if the data is < 100.
0
 
LVL 6

Expert Comment

by:ViceroyFizzlebottom
ID: 24379343
Whoops, in my last line I meant "if the data > 100"
0
 
LVL 2

Author Comment

by:badstyle
ID: 24380069
hmm that's a little awkward, as there may be occasions when the data is less than the maximum required...

Is it possible to interrogate the data so that even if it is less than 100 it will still work?

Better than that... is it possible to interrogate the data so as not to clip words, or even round it to the nearest full stop? If so can you provide a solution on how that would work?

Thanks for your speedy assistance, really appreciate it!
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LVL 6

Assisted Solution

by:ViceroyFizzlebottom
ViceroyFizzlebottom earned 50 total points
ID: 24380263
Below is a sample of something that would work. If the total length is > 100, we only work with the first 100 characters, taking from that the last space position (which we'll assume here is a word break).



string s = dr["NewsStory"].ToString();

string truncatedText = String.Empty;
 

if(s.Length > 100)

{

    truncatedText = s.Substring(0, 100).Substring(0, s.LastIndexOf(" "));

}
 

objx.WriteElementString("description", truncatedText + "...");

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LVL 6

Assisted Solution

by:ViceroyFizzlebottom
ViceroyFizzlebottom earned 50 total points
ID: 24380316
Actually in the code above, you can't append the last .Substring() (My brain was in LINQ mode). So it would end up as:

truncatedText = s.Substring(0,100);
truncatedText = truncatedText.Substring(0, truncatedText.LastIndexOf(" "));

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LVL 3

Accepted Solution

by:
channa_m earned 75 total points
ID: 24387276
How about something like this,


        Dim newsStory = dr("NewsStory").ToString

        Dim len = newsStory.Length - 1
 

        If len > 100 Then

            len = 100

        End If
 

        newsStory = newsStory.SubString(0, len)

        objX.WriteElementString("description", newsStory & "..")

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Author Closing Comment

by:badstyle
ID: 31581198
Although both gave desirable results I preferred Channa M's solution on the basis that it would show part of the parameters value even though its content may have contained less than the substrings maximum length.

Many thanks people!
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