'xi' is an undeclared prefix when setting InnerXml of new XmlDocumentFragment

Question

I'm attempting to add a new node to an existing xml file. The file has the xi namespace defined:

<Module xmlns:xi="http://www.w3.org/2001/XInclude" ...

and contains nodes with:

<xi:include href="somefile.xml" />

This loads fine, and I can operate on the existing nodes, but if I try to add a new node like so:

XmlDocumentFragment frag = doc.CreateDocumentFragment();
frag.InnerXml =
    "<SomeNode SomeAttribute=\"\">" +
    "    <xi:include href=\"SomeFile.xml\" />" +
    "</SomeNode>";

I get an XmlException for "'xi' is an undeclared prefix"

I presume it is unhappy that the fragment itself does not recognize the namespace, but I'm not seeing any intuitive way to fix this.

Answer 1

As I was writing this question, I had an idea that worked and am posting it in case it helps someone else. I decided to add the offending xml after adding the fragment to the document:

XmlDocumentFragment frag = doc.CreateDocumentFragment();
frag.InnerXml =
    "<SomeNode SomeAttribute=\"\">" +
    "</SomeNode>";

XmlNode newNode = parentNode.AppendChild(frag);
newNode.InnerXml = "<xi:include href=\"SomeFile.xml\" />";

If someone has a cleaner way to do this. I am interested to hear what it is.

Answer 2

在<xi:include href="somefile.xml" />中，xi是名称空间前缀。

如果使用，则必须声明命名空间前缀。您必须添加使用名称空间前缀xi的元素或其上方，其声明：

xmlns:xi="http://www.w3.org/2001/XInclude" 

如果您temporarily managed to skirt an error message by assembling fragments in a certain manner，请认识到最终结果是重要的：如果使用了名称空间但未声明，则仍然存在问题。