Develop Reference

How do I create an XElement that contains a prefix without a wrapper?

I'm trying to create a simple empty XElement like this:
<dyn:Positions>
<Vector2-Array>
</Vector2-Array>
</dyn:Positions>
I have the namespace defined above:
XNamespace dyn = "https://www.abc.at/dyn";
But when I create the XElement:
XElement positions = new XElement(dyn + "Positions", new XElement("Vector2-Array"));
It comes out like this:
<Positions xmlns="dyn">
<Vector2-Array xmlns="" />
</Positions>
Is that possible without wrapping it in another XElement? Because I need this element to be appended in another document later, after more elements are added inside.

I think you want Vector2-Array to be in the same namespace as Positions, and then you don't see it in the output:
XElement positions = new XElement(dyn + "Positions",
new XElement(dyn + "Vector2-Array"));
this gives
<Positions xmlns="https://www.abc.at/dyn">
<Vector2-Array />
</Positions>
the dyn: notation is just a shorthand, it should not matter when you later merge this in some parent XML. You should be very sure about which namespace everything belongs to.

Because you're not adding your namespace declaration, the dyn namespace becomes the default.
Then, when you add the child element without a namespace, a namespace declaration with no namespace has to be added to indicate it is not within the default namespace.
If your dyn namespace is not meant to be the default namespace, try the following code:
XNamespace dyn = "https://www.abc.at/dyn";
XElement positions = new XElement(
dyn + "Positions",
new XAttribute(XNamespace.Xmlns + "dyn", "https://www.abc.at/dyn"),
new XElement("Vector2-Array"));
This produces the following output:
<dyn:Positions xmlns:dyn="https://www.abc.at/dyn">
<Vector2-Array />
</dyn:Positions>
Note that when you start appending this element to other documents, you may get more behaviour similar to your original problem if there's any mismatches of namespaces.
The OP has specifically brought up the subject of appending this element to another element that also contains the namespace declaration.
I've created this code to test:
XNamespace dyn = "https://www.abc.at/dyn";
XElement positions = new XElement(
dyn + "Positions",
new XAttribute(XNamespace.Xmlns + "dyn", "https://www.abc.at/dyn"),
new XElement("Vector2-Array"));
XElement root = new XElement(
dyn + "root",
new XAttribute(XNamespace.Xmlns + "dyn", "https://www.abc.at/dyn"));
root.Add(positions);
When using the debugger, the XML of the root element after adding Positions is this:
<dyn:root xmlns:dyn="https://www.abc.at/dyn">
<dyn:Positions xmlns:dyn="https://www.abc.at/dyn">
<Vector2-Array />
</dyn:Positions>
</dyn:root>
So the namespace declaration is duplicated.
However, there is a SaveOption of OmitDuplicateNamespaces that can be used when saving or formatting the XML to string:
Console.WriteLine(root.ToString(SaveOptions.OmitDuplicateNamespaces));
The resulting output of this is as below:
<dyn:root xmlns:dyn="https://www.abc.at/dyn">
<dyn:Positions>
<Vector2-Array />
</dyn:Positions>
</dyn:root>
Because the duplicate namespace declarations effectively do nothing (even though they're ugly) they can be removed this way, if the displaying of the XML is the important thing.
Functionally, having duplicated namespace declarations doesn't actually do anything as long as they match.

linq to xml duplicate namespace gives empty attribute

<ftc:XX version="1.1"
xmlns:ftc="urn:v1"
xmlns="urn:v1">
<ftc:YY>
<SIN>000000</SIN>
<Country>CA</Country>
</ftc:YY>
</ftc:XX>
this is the what i need to create. but when i create this, it shows empty namespace in the SIN and Country tag. i need to remove that. can anyone guide me?
this is the code which i use,
XNamespace ftc = "urn:v1";
XElement XX = new XElement(ftc + "XX",
new XAttribute(XNamespace.Xmlns + "ftc", ftc.NamespaceName),
new XAttribute("xmlns", ftc.NamespaceName),
new XAttribute("version","1.1"),
new XElement(ftc + "YY",
XElement("SIN", "000000"),
new XElement("Country", "CA")
)
)
with this, what i get is like this.
<ftc:XX version="1.1"
xmlns:ftc="urn:v1"
xmlns="urn:v1">
<ftc:YY>
<SIN xmlns="">000000</SIN>
<Country xmlns="">CA</Country>
</ftc:YY>
</ftc:XX>
but i need without this part.
xmlns=""

SIN and Country belong to the urn:v1 namespace. Your document has a default namespace of urn:v1 so all elements without an explicit namespace prefix will belong to that namespace.
When you created those elements, they were in the empty namespace, so that extra namespace declaration needed to be generated.
XNamespace ftc = "urn:v1";
var doc = new XDocument(
new XElement(ftc + "XX",
new XAttribute("version", "1.1"),
new XAttribute(XNamespace.Xmlns + "ftc", ftc),
new XAttribute("xmlns", ftc),
new XElement(ftc + "YY",
new XElement(ftc + "SIN", "000000"),
new XElement(ftc + "Country", "CA")
)
)
);
<XX version="1.1" xmlns:ftc="urn:v1" xmlns="urn:v1">
<YY>
<SIN>000000</SIN>
<Country>CA</Country>
</YY>
</XX>
Note that since your explicit namespace ftc and the default namespace are equal, none of the prefixes will be generated as you expect. This isn't configurable on a per element level as far as I know.

Little help using XmlTextWriter on writing "xhtml:link" element of sitemap.xml

Hello I'm trying to write a string like :
<xhtml:link rel="alternate" hreflang="de" href="http://www.example.com/de" />
using XmlTextWriter class
I've tried this piece of code:
// Write Alternative links
_writer.WriteStartElement("xhtml:link");
_writer.WriteAttributeString("rel","alternate");
_writer.WriteAttributeString("hreflang", "de");
_writer.WriteAttributeString("href", "http://example.com/de");
_writer.WriteEndElement();
Which generates this error:
Namespace prefix xhtml on link is not defined
But I don't need any namespaces provided for xhtml:link
Question: How to achieve the string that I need using XmlTextWriter?
Update 1: I have changed to LINQ to XML
But for now I have another problem... For the beginning I'll show the code:
private readonly XNamespace nsXhtml = "http://www.w3.org/1999/xhtml";
private readonly XNamespace nsSitemap = "http://www.sitemaps.org/schemas/sitemap/0.9";
private readonly XNamespace nsXsi = "http://www.w3.org/2001/XMLSchema-instance";
private readonly XNamespace nsLocation = "http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd";
public XDocument Generate()
{
var sitemap = new XDocument(new XDeclaration("1.0", "utf-8", "yes"));
var urlSet = new XElement(nsSitemap + "urlset",
new XAttribute("xmlns", nsSitemap),
new XAttribute(XNamespace.Xmlns + "xhtml", nsXhtml),
new XAttribute(XNamespace.Xmlns + "xsi", nsXsi),
new XAttribute(nsXsi + "schemaLocation", nsLocation),
from node in GenerateUrlNodes() // Provides a collection of "objects", actually it doesn't matter since we anyway convert them to XElement below...
select WriteUrlLocation(node.Url,node.UpdateFrequency,node.LastModified));
sitemap.Add(urlSet);
return sitemap;
}
protected XElement WriteUrlLocation(string url, UpdateFrequency updateFrequency, DateTime lastUpdated)
{
var urlNode = new XElement(nsSitemap + "url",
new XElement(nsSitemap + "loc", url),
new XElement(nsSitemap + "changefreq", updateFrequency),
new XElement(nsSitemap + "lastmod", lastUpdated)
);
var linkNode = new XElement(nsXhtml + "link",
new XAttribute("rel", "alternate"),
new XAttribute("hreflang", "de"),
new XAttribute("href", "http://example.com/de"));
urlNode.Add(linkNode);
return urlNode;
}
The problem is that When I inspect the Generated sitemap at Controller:
public ActionResult Sitemap()
{
var sitemap = _sitemapGenerator.Generate().ToString();
return Content(sitemap,"text/xml");
}
The whole xml is not as expected and, the <xhtml:link> element is rendered with a non-empty closing tag (thus I don't know if this is a problem here) .. Look at the image please
Update 2: Solved! Seems that the XML structure is valid but the browser is not displaying it right...

You should change to use a different overload of XmlWriter.StartElement. For example:
_writer.WriteStartElement("link", "http://www.w3.org/1999/xhtml");
That assumes you've already got a prefix alias of xhtml for the namespace http://www.w3.org/1999/xhtml. I'd still recommend shifting to use LINQ to XML as soon as you can though... XmlWriter is great for cases where you really need to stream the data (e.g. when it's huge) but otherwise, LINQ to XML makes things a lot easier:
XNamespace xhtml = "http://www.w3.org/1999/xhtml";
var element = new XElement(xhtml + "link",
new XAttribute("rel", "alternate"),
new XAttribute("hreflang", "de"),
new XAttribute("href", "http://example.com/de"));
parent.Add(element);

If you will use XML Writer and write this
<xhtml:link rel="alternate" hreflang="en" href="www.yoursite.com" />
you can choose this code for .NET CORE 2.0:
foreach (SitemapNodeAlternate a in alternate)
{
MyWriter.WriteStartElement("xhtml", "link", null);
MyWriter.WriteAttributeString("rel", "alternate");
MyWriter.WriteAttributeString("href", a.href);
MyWriter.WriteAttributeString("hreflang", a.hreflang);
MyWriter.WriteEndElement();
}

The prefix " cannot be redefined from " to <url> within the same start element tag

I'm trying to generate the following xml element using C#.
<Foo xmlns="http://schemas.foo.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://schemas.foo.com
http://schemas.foo.com/Current/xsd/Foo.xsd">
The problem that I'm having is that I get the exception:
The prefix " cannot be redefined from " to within the same start
element tag.
This is my c# code:
XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";
XElement foo = new XElement("Foo", new XAttribute("xmlns", "http://schemas.foo.com"),
new XAttribute(XNamespace.Xmlns + "xsi", "http://www.w3.org/2001/XMLSchema-instance"),
new XAttribute(xsi + "schemaLocation", "http://schemas.foo.com http://schemas.foo.com/Current/xsd/Foo.xsd"));
How can I fix this? I'm trying to send the generated xml as the body of a SOAP message and I need it to be in this format for the receiver.
EDIT: I found my answer on another question. Controlling the order of XML namepaces

You need to indicate that the element Foo is part of the namespace http://schemas.foo.com. Try this:
XNamespace xNamespace = "http://schemas.foo.com";
XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";
XElement foo = new XElement(
xNamespace + "Foo",
new XAttribute("xmlns", "http://schemas.foo.com"),
new XAttribute(XNamespace.Xmlns + "xsi", "http://www.w3.org/2001/XMLSchema-instance"),
new XAttribute(xsi + "schemaLocation", "http://schemas.foo.com http://schemas.foo.com/Current/xsd/Foo.xsd")
);

I was getting this error when creating an XDocument. After a lot of googling I found this article:
http://www.mikesdotnetting.com/Article/111/RSS-Feeds-and-Google-Sitemaps-for-ASP.NET-MVC-with-LINQ-To-XML
There just happens to be an explanation part way through the doc, that I was lucky enough to spot.
The key point is that your code should let the XDocument handle the xmlns attribute. When creating an XElement, your first instinct would be to set the namespace attribute like all the rest, by adding an attribute "xmlns" and setting it to a value.
Instead, you should create an XNamespace variable, and use that XNamespace variable when defining the XElement. This will effectively add an XAttribute to your element for you.
When you add an xmlns attribute yourself, you are telling the XElement creation routine to create an XElement in no namespace, and then to change the namespace using the reserved xmlns attribute. You are contradicting yourself. The error says "You cannot set the namespace to empty, and then set the namespace again to something else in the same tag, you numpty."
The function below illustrates this...
private static void Test_Namespace_Error(bool doAnError)
{
XDocument xDoc = new XDocument();
string ns = "http://mynamespace.com";
XElement xEl = null;
if (doAnError)
{
// WRONG: This creates an element with no namespace and then changes the namespace
xEl = new XElement("tagName", new XAttribute("xmlns", ns));
}
else
{
// RIGHT: This creates an element in a namespace, and implicitly adds an xmlns tag
XNamespace xNs = ns;
xEl = new XElement(xNs + "tagName");
}
xDoc.Add(xEl);
Console.WriteLine(xDoc.ToString());
}

Others explain why this is happening but it still took me a while to work out how to fix it for me. I was trying to add some external XML to an XML document.
What finally worked for me was:
ElementTree.register_namespace("mstts", "https://www.w3.org/2001/mstts")
ElementTree.register_namespace("", "http://www.w3.org/2001/10/synthesis")
xml_body = ElementTree.fromstring(
'<speak version="1.0"'
' xmlns:mstts="https://www.w3.org/2001/mstts"'
' xmlns="http://www.w3.org/2001/10/synthesis"'
f' xml:lang="{locale}">'
f' <voice name="{azure_voice}">'
' <mstts:silence type="Leading" value="0" />'
' <prosody rate="-10.00%">'
f' {utterance}'
' </prosody>'
' <mstts:silence type="Tailing" value="0" />'
' </voice>'
'</speak>'

LINQ to XML - How to fix default namespace in the root element

Consider generating the following XML structure, which has 2 prefixed namespaces:
XNamespace ns1 = "http://www.namespace.org/ns1";
const string prefix1 = "w1";
XNamespace ns2 = "http://www.namespace.org/ns2";
const string prefix2 = "w2";
var root =
new XElement(ns1 + "root",
new XElement(ns1 + "E1"
, new XAttribute(ns1 + "attr1", "value1")
, new XAttribute(ns2 + "attr2", "value2"))
, new XAttribute(XNamespace.Xmlns + prefix2, ns2)
, new XAttribute(XNamespace.Xmlns + prefix1, ns1)
);
It generates the following XML result (which is fine):
<w1:root xmlns:w2="http://www.namespace.org/ns2" xmlns:w1="http://www.namespace.org/ns1">
<w1:E1 w1:attr1="value1" w2:attr2="value2" />
</w1:root>
The problem arises when I try to change ns1 from a prefixed namespace to a default namespace by commenting out its XML declaration, as in:
var root =
new XElement(ns1 + "root",
new XElement(ns1 + "E1"
, new XAttribute(ns1 + "attr1", "value1")
, new XAttribute(ns2 + "attr2", "value2"))
, new XAttribute(XNamespace.Xmlns + prefix2, ns2)
//, new XAttribute(XNamespace.Xmlns + prefix1, ns1)
);
which produces:
<root xmlns:w2="http://www.namespace.org/ns2" xmlns="http://www.namespace.org/ns1">
<E1 p3:attr1="value1" w2:attr2="value2" xmlns:p3="http://www.namespace.org/ns1" />
</root>
Note the duplicate namespace definitions in root and E1 and attributes prefixed as p3 under E1. How can I avoid this from happening? How can I force declaration of default namespace in the root element?
Related Questions
I studied this question: How to set the default XML namespace for an XDocument
But the proposed answer replaces namespace for elements without any namespace defined. In my samples the elements and attributes already have their namespaces correctly set.
What I have tried
Based on too many trial and errors, it seems to me that attributes which are not directly under the root node, where the attribute and its direct parent element both have the same namespace as the default namespace; the namespace for the attribute needs to be removed!!!
Based on this I defined the following extension method which traverses all the elements of the resulting XML and performs the above. In all my samples thus far this extension method fixed the problem successfully, but it doesn't necessarily mean that somebody can't produce a failing example for it:
public static void FixDefaultXmlNamespace(this XElement xelem, XNamespace ns)
{
if(xelem.Parent != null && xelem.Name.Namespace == ns)
{
if(xelem.Attributes().Any(x => x.Name.Namespace == ns))
{
var attrs = xelem.Attributes().ToArray();
for (int i = 0; i < attrs.Length; i++)
{
var attr = attrs[i];
if (attr.Name.Namespace == ns)
{
attrs[i] = new XAttribute(attr.Name.LocalName, attr.Value);
}
}
xelem.ReplaceAttributes(attrs);
}
}
foreach (var elem in xelem.Elements())
elem.FixDefaultXmlNamespace(ns);
}
This extension method produces the following XML for our question, which is what I desire:
<root xmlns:w2="http://www.namespace.org/ns2" xmlns="http://www.namespace.org/ns1">
<E1 attr1="value1" w2:attr2="value2" />
</root>
However I don't like this solution, mainly because it is expensive. I feel I'm missing a small setting somewhere. Any ideas?

Quoting from here:
An attribute is not considered a child of its parent element. An attribute never inherits the namespace of its parent element. For that reason an attribute is only in a namespace if it has a proper namespace prefix. An attribute can never be in a default namespace.
and here:
A default namespace declaration applies to all unprefixed element names within its scope. Default namespace declarations do not apply directly to attribute names; the interpretation of unprefixed attributes is determined by the element on which they appear.
It seems that this odd behavior of LINQ-to-XML is rooted in standards. Therefore whenever adding a new attribute its namespace must be compared against the parents' default namespace which is active in its scope. I use this extension method for adding attributes:
public static XAttribute AddAttributeNamespaceSafe(this XElement parent,
XName attrName, string attrValue, XNamespace documentDefaultNamespace)
{
if (newAttrName.Namespace == documentDefaultNamespace)
attrName = attrName.LocalName;
var newAttr = new XAttribute(attrName, attrValue);
parent.Add(newAttr);
return newAttr;
}
And use this extension method for retrieving attributes:
public static XAttribute GetAttributeNamespaceSafe(this XElement parent,
XName attrName, XNamespace documentDefaultNamespace)
{
if (attrName.Namespace == documentDefaultNamespace)
attrName = attrName.LocalName;
return parent.Attribute(attrName);
}
Alternatively, if you have the XML structure at hand and want to fix the namespaces already added to attributes, use the following extension method to fix this (which is slightly different from that outlined in the question):
public static void FixDefaultXmlNamespace(this XElement xelem,
XNamespace documentDefaultNamespace)
{
if (xelem.Attributes().Any(x => x.Name.Namespace == documentDefaultNamespace))
{
var attrs = xelem.Attributes().ToArray();
for (int i = 0; i < attrs.Length; i++)
{
var attr = attrs[i];
if (attr.Name.Namespace == documentDefaultNamespace)
{
attrs[i] = new XAttribute(attr.Name.LocalName, attr.Value);
}
}
xelem.ReplaceAttributes(attrs);
}
foreach (var elem in xelem.Elements())
elem.FixDefaultXmlNamespace(documentDefaultNamespace);
}
Note that you won't need to apply the above method, if you have used the first two methods upon adding and retrieving attributes.

I have found something for you, from the C# in a Nutshell book:
You can assign namespaces to attributes too. The main difference is that it always
requires a prefix. For instance:
<customer xmlns:nut="OReilly.Nutshell.CSharp" nut:id="123" />
Another difference is that an unqualified attribute always has an empty namespace:
it never inherits a default namespace from a parent element.
So given your desired output i have made a simple check.
var xml = #"<root xmlns:w2=""http://www.namespace.org/ns2"" xmlns=""http://www.namespace.org/ns1"">
<E1 attr1=""value1"" w2:attr2=""value2"" />
</root>";
var dom = XElement.Parse(xml);
var e1 = dom.Element(ns1 + "E1");
var attr2 = e1.Attribute(ns2 + "attr2");
var attr1 = e1.Attribute(ns1 + "attr1");
// attr1 is null !
var attrNoNS = e1.Attribute("attr1");
// attrNoNS is not null
So in short attr1 does not have default namespace, but has an empty namespace.
Is this you want? If yes, just create you attr1 without namespace...
new XAttribute("attr1", "value1")