how to get namespaces in scope from XmlReader

Question

I need to implement serializable type for element which contains a sequence of any elements with XPath-like expressions. It has very simple scheme:

<xsd:complexType name="FilterType">
    <xsd:sequence>
        <xsd:any minOccurs="0" maxOccurs="unbounded" />
    </xsd:sequence>
</xsd:complexType>

The semantic of this element is described in WSBaseNotification topic 4.2. The problem is that to interpret an expression we need some mechanism to resolve prefixes that was used in it (XmlReader provide such functionality via LookupNamespace). But there is another problem that it is not possible to parse expression at this stage, we even can not make any assumptions about expression type and dialect at this moment. So we need somehow collect all defined prefixes in that scope. Some of XmlReader-s (for example XmlTextReader) implements interface IXmlNamespaceResolver which provide such functionality via GetNamespacesInScope but many of them didn't (for example XmlMtomReader). This type used in many web service requests, the web service use wcf framework and have several bindings, so we can not make any assumption about what XmlReader will be used. Here is prototype implementation of such type, if we have GetNamespacesInScope for XmlReader:

[Serializable]
public class FilterType : IXmlSerializable {
public XElement[] Any;
public void ReadXml(XmlReader reader) {
    var xelist = new LinkedList<XElement>();
    reader.Read();
    var dr = reader as XmlDictionaryReader;
    var gns = reader.GetNamespacesInScope(); // need to implement

    while (reader.NodeType != XmlNodeType.EndElement) {
        if (reader.NodeType == XmlNodeType.Element) {
            var x = XElement.ReadFrom(reader) as XElement;
            foreach (var ns in gns) {
                var pref = ns.Key;
                var uri = ns.Value;
                if (x.GetNamespaceOfPrefix(pref) == null) {
                    x.Add(new XAttribute(XName.Get(pref, "http://www.w3.org/2000/xmlns/"), uri));
                }
            }
            xelist.AddLast((XElement)x);
        } else {
            reader.Skip();
        }
    }
    Any = xelist.ToArray();
    reader.ReadEndElement();
}

public void WriteXml(XmlWriter writer) {
    if (Any != null) {
        foreach (var x in Any) {
            x.WriteTo(writer);
        }
    }
}

public XmlSchema GetSchema() {
    return null;
}
}

Is there any way to implement GetNamespacesInScope for every possible XmlReader? Or maybe there is another solution?

Answer 1

I use the code like this :

        XPathDocument doc = new XPathDocument("catalog.xml");
        XPathNavigator nav = doc.CreateNavigator();
        var v = nav.GetNamespacesInScope(XmlNamespaceScope.All);

Hope it helps, Radu

Answer 2

You may, however, need a namespace-manager - for example:

XmlElement el = ...; //TODO
XmlNamespaceManager nsmgr = new XmlNamespaceManager(
    el.OwnerDocument.NameTable);
nsmgr.AddNamespace("x", el.OwnerDocument.DocumentElement.NamespaceURI);
var nodes = el.SelectNodes(@"/x:outerelement/x:innerelement", nsmgr);