Question

I have a little problem that perhaps you can help me with.

I try to use the XmlWriter to write an XML-tag that looks like this (w3c feed recommendation):

<atom:link href='http://localhost' rel='self' type='application/rss+xml' /> 

The problem is that I can’t use the WriteStartElement-method as I would want to (atom as a prefix and link as the element name), since this gives me a ‘ArgumentException: Cannot use a prefix with an empty namespace‘.

My code looks like this:

public void WriteTo(XmlWriter writer, Feed feed) {     // RSS element     writer.WriteStartElement('rss', '');     writer.WriteAttributeString('version', '2.0');     writer.WriteAttributeString('xmlns', 'atom', string.Empty, 'http://www.w3.org/2005/Atom');      // Channel element     writer.WriteStartElement('channel');      // The link to the feed.     writer.WriteStartElement('link', 'atom');     writer.WriteAttributeString('href', feed.FeedUrl.ToString());     writer.WriteAttributeString('rel', 'self');     writer.WriteAttributeString('type', 'application/rss+xml');     writer.WriteEndElement();      // Feed information     writer.WriteElementString('title', feed.Title);     writer.WriteElementString('description', feed.Description);     writer.WriteElementString('link', feed.Link.ToString());      // Iterate through all items.     foreach (FeedItem item in feed.Items)     {         writer.WriteStartElement('item');         writer.WriteElementString('title', item.Title);         writer.WriteElementString('link', item.Link.ToString());         writer.WriteElementString('description', item.Description);         writer.WriteElementString('guid', item.Guid);         writer.WriteEndElement();     }      // Channel element end     writer.WriteEndElement();      // RSS element end     writer.WriteEndElement(); } 

I assume that my problem is trivial and can easily be solved, but how?

UPDATE:

The problem is solved. Check Jon Skeets answer for the solution.

Answer 1

Why not just use the appropriate namespace (http://www.w3.org/2005/Atom)?

You could write the namespace declaration earlier, in which case you only need the WriteStartElement overload which takes the element name and namespace – I think the prefix is then used automatically.