How to declared namespace prefix in SOAP header

Question

I'm using following code to add header to soap header.

using (new OperationContextScope(client.InnerChannel))
{
    OperationContext.Current.OutgoingMessageHeaders.Add(
        MessageHeader.CreateHeader("ns:To", "", "http://###.com"));                                
}

But I got undeclared namespace prefix ns error, I will need add xmlns:ns="http://www.w3.org/2005/08/addressing" to name space.

So my question is how to add namespace prefix to

<s:Envelope>
    <s:Header>
        <ns:To>##</ns:To>
    </s:Header>
</s:Envelope>

To

<s:Envelope>
    <s:Header xmlns:ns="http://www.w3.org/2005/08/addressing">
        <ns:To>##</ns:To>
    </s:Header>
</s:Envelope>

Answer 1

Try this:

String oasisWsSecNS = "http://www.w3.org/2005/08/addressing";
XmlDocument document = new XmlDocument();
     
XmlElement child = document.CreateElement("To", oasisWsSecNS);
child.AppendChild(document.CreateTextNode("[value]"));
element.AppendChild(child);
            
context.OutgoingMessageHeaders.Add(MessageHeader.CreateHeader("Header", oasisWsSecNS, document.DocumentElement));