XElement adds an xmlns

问题:

I'm using Linq to XML to create a new XML file. Some part of the file do I get from an existing XML file. I use the following code for this.

var v2 = new XDocument(
  new XDeclaration("1.0", "utf-16", ""),
  new XComment(string.Format("Converted from version 1. Date: {0}", DateTime.Now)),
  new XElement(ns + "keyem",
    new XAttribute(XNamespace.Xmlns + "xsd", xsd.NamespaceName),
    new XAttribute(XNamespace.Xmlns + "xsi", xsi.NamespaceName),
    new XAttribute(xsi + "schemaLocation", schemaLocation.NamespaceName),
    new XAttribute("version", "2"),
    new XAttribute("description", description),
    new XElement(ns + "layout",
      new XAttribute("type", type),
      new XAttribute("height", height),
      new XAttribute("width", width),
      settings.Root)       // XML from an existing file

The problem is that it adds xmlns = "" the first element from the existing file.

The result is:

<?xml version="1.0" encoding="utf-16"?>
<foo 
  xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://tempuri.org/KeyEmFileSchema.xsd KeyEmFileSchema.xsd"
  xmlns="http://tempuri.org/KeyEmFileSchema.xsd">
  <settings xmlns="">
      ...
  </settings>
</foo>

The XML file I'm reading from looks like this, but I can change it if needed

<?xml version="1.0" encoding="utf-16"?>
<settings>
  <colormaps>
    <colormap color="Gray"     textcolor="Black"/>
    <colormap color="DarkGray" textcolor="White"/>
    <colormap color="Black"    textcolor="White"/>
    <colormap color="Cyan"     textcolor="Black"/>
  </colormaps>
  <macromaps>
    <macromap pattern="^@([0-9A-F]{2})\|([0-9A-F]{2})$"  replace="{ESC}$1{ESC}$2{MOUSERESET}"/>
    <macromap pattern="^\$([0-9A-F]{2})\|([0-9A-F]{2})$" replace="{USERCLICK}{ESC}$1{ESC}$2{MOUSERESET}"/>
    <macromap pattern="^\$([0-9A-F]{2})$"                replace="{USERCLICK}{ESC}$1"/>
  </macromaps>
  <keydefault color="Cyan"/>
  <groupdefault color="DarkGray"/>
</settings>

回答1:

You're seeing this because the settings element (presumably coming from your document) does not live in this namespace. It lives in the default/null-uri namespace.

You would need to transform your input document in order to change it's namespace.

This somewhat simplified example take your xml file and places it into another document but, before it does so, it changes the namespace of every element in that xml file to that of your target document...

    static void ProcessXmlFile()
    {
        XNamespace ns = "http://tempuri.org/KeyEmFileSchema.xsd/";

        // load the xml document
        XElement settings = XElement.Load("data.xml");

        // shift ALL elements in the settings document into the target namespace
        foreach (XElement e in settings.DescendantsAndSelf())
        {
            e.Name = ns + e.Name.LocalName;
        }

        // write the output document
        var file = new XDocument(new XElement(ns + "foo",
                                        settings));

        Console.Write(file.ToString());            
    }

The result of which this...

<foo xmlns="http://tempuri.org/KeyEmFileSchema.xsd/">
  <settings>
    <colormaps>
      <colormap color="Gray" textcolor="Black" />
      <colormap color="DarkGray" textcolor="White" />
      <colormap color="Black" textcolor="White" />
      <colormap color="Cyan" textcolor="Black" />
    </colormaps>
    <macromaps>
      <macromap pattern="^@([0-9A-F]{2})\|([0-9A-F]{2})$" replace="{ESC}$1{ESC}$2{MOUSERESET}" />
      <macromap pattern="^\$([0-9A-F]{2})\|([0-9A-F]{2})$" replace="{USERCLICK}{ESC}$1{ESC}$2{MOUSERESET}" />
      <macromap pattern="^\$([0-9A-F]{2})$" replace="{USERCLICK}{ESC}$1" />
    </macromaps>
    <keydefault color="Cyan" />
    <groupdefault color="DarkGray" />
  </settings>
</foo>

As you can see, the settings element is now in the same namespace as the foo element. This is essentially a quick and dirty xml transform, and clearly it doesn't respect any namespaces in the xml doc you're importing. But this might be what you're after, or might at least form the basis of something more robust.

回答2:

You could write an extension method for this. This method has a return value so it supports chaining, but also changes transformation of the original so it can be used without assignment.

public static XElement EnsureNamespaceExists(this XElement xElement, XNamespace xNamespace)
{
    string nodeName = xElement.Name.LocalName;

    if (!xElement.HasAttribute("xmlns"))
    {
        foreach (XElement tmpElement in xElement.DescendantsAndSelf())
        {
            tmpElement.Name = xNamespace + tmpElement.Name.LocalName;
        }
        xElement = new XElement(xNamespace + nodeName, xElement.FirstNode);
    }

    return xElement;
}