Adding multiple namespace declarations in XmlWriter

Question

I am trying to write out the following element using XmlWriter

<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom"> 

I've got the very first declaration done using

writer.WriteStartElement("kml", "http://www.opengis.net/kml/2.2"); 

How can I add the remaining 3 declarations to the same element?

Answer 1

writer.WriteAttributeString("xmlns","gx", null, "http://www.google.com/kml/ext/2.2"); writer.WriteAttributeString("xmlns","kml", null, "http://www.opengis.net/kml/2.2"); writer.WriteAttributeString("xmlns","atom", null, "http://www.w3.org/2005/Atom"); 

Got that from https://msdn.microsoft.com/en-us/library/cfche0ka(v=vs.100).aspx.

Answer 2

The answer of Ryan B is incomplete as the XML namespace is only written as attribute but not registered in the name table, so LookupPrefix will fail getting prefix of one of the XML namespaces, f.i. http://www.w3.org/2005/Atom. It will return null instead atom.

To write a namespace attribute and get namespace registered use

writer.WriteAttributeString("atom",                             "http://www.w3.org/2000/xmlns/",                             "http://www.w3.org/2005/Atom"); 

Use of namespace http://www.w3.org/2000/xmlns/registers also the prefix in name table.