Develop Reference

Correct way to add a namespace to an element using XmlDocument

I have to modify a incoming SOAP XML message to add a namespace to one of the elements so that the deserialisation will work. However when I add the xmlns attribute to the correct element, I get an error when I try to load the xml in to an XmlWriter via a stream (which I need to do to in my IClientMessageInspector implementation to replace the Message reply).
The prefix '' cannot be redefined from '' to 'http://www.example.com' within the same start element tag.
I have a work around, which is that after I've modifed the attribute, I reload the entire XML document from it's own OuterXML. This works for some reason, but makes me think there must be a 'correct' way to do this.
Here's a sample test that demonstrates the problem and my current solutions:
[Test]
public void XmlNamespaceTest()
{
var originalXmlString = "<?xml version=\"1.0\" encoding=\"utf-8\"?><TestElement><Child>thing</Child></TestElement>";
var desiredXmlString = "<?xml version=\"1.0\" encoding=\"utf-8\"?><TestElement xmlns=\"http://www.example.com\"><Child>thing</Child></TestElement>";
var doc = new XmlDocument();
doc.LoadXml(originalXmlString);
Assert.That(originalXmlString, Is.EqualTo(doc.OuterXml));
// Write this document via an XMLWriter
var ms = new MemoryStream();
var xmlWriter = XmlWriter.Create(ms);
doc.WriteTo(xmlWriter);
xmlWriter.Flush();
ms.Position = 0;
StreamReader sr = new StreamReader(ms);
var originalXmlViaXmlWriter = sr.ReadToEnd();
Assert.That(originalXmlString, Is.EqualTo(originalXmlViaXmlWriter));
// Add the namespace to the element
((XmlElement)doc.GetElementsByTagName("TestElement").Item(0))?.SetAttribute("xmlns", "http://www.example.com");
Assert.That(desiredXmlString, Is.EqualTo(doc.OuterXml));
// Now attempt to write this modified xml via an XMLWriter
ms.SetLength(0);
xmlWriter = XmlWriter.Create(ms);
//Uncomment line below to fix the error.
//doc.LoadXml(doc.OuterXml);
doc.WriteTo(xmlWriter);
xmlWriter.Flush();
ms.Position = 0;
sr = new StreamReader(ms);
var modifedXmlViaXmlWriter = sr.ReadToEnd();
Assert.That(desiredXmlString, Is.EqualTo(modifedXmlViaXmlWriter));
}

According to this you can't change an elements namespace in an XmlDocument. This is also what #LocEngineer found in his comment. The referenced article mentions that the only way to do this is to save and reload the XmlDocument, which is exactly what you are doing.
If you are in a position to use XDoxument instead, it is possible. See this answer for a solution.

C# XML can't load indent value

The code below is causing the " Data at the root level is invalid. Line 1, position 1. "
I like to keep the code indent(linebreak) but keep having the problem as mentioned above. I could use the TextReader to load the xml but it will remove the indent which i don't like it. If you know how to fix problem please let me know. Thanks
public XmlDocument MYXML()
{
XmlWriterSettings wSettings = new XmlWriterSettings();
wSettings.Indent = false;
wSettings.OmitXmlDeclaration = false;
MemoryStream ms = new MemoryStream();
XmlWriter xw = XmlWriter.Create(ms, wSettings);// Write Declaration
xw.WriteStartDocument();
// Write the root node
xw.WriteStartElement("Library");
// Write the books and the book elements
xw.WriteStartElement("Book");
xw.WriteStartAttribute("BookType");
xw.WriteString("Hardback");
xw.WriteEndAttribute();
xw.WriteStartElement("Title");
xw.WriteString("Door Number Three");
xw.WriteEndElement();
xw.WriteStartElement("Author");
xw.WriteString("O'Leary, Patrick");
xw.WriteEndElement();
xw.WriteEndElement();
xw.WriteEndElement();
// Close the document
xw.WriteEndDocument();
// Flush the write
xw.Flush();
Byte[] buffer = new Byte[ms.Length];
buffer = ms.ToArray();
string xmlOutput = System.Text.Encoding.UTF8.GetString(buffer);
//The next 3 line works fine but it will remove the Indent from the XmlWriterSettings
//TextReader tr = new StreamReader(ms);
//ms.Seek(0, SeekOrigin.Begin);
//xmlOutput = tr.ReadToEnd() + "";
//Can't nload the xmlOutput from buffer
XmlDocument xmldoc = new XmlDocument();
xmldoc.LoadXml(xmlOutput);
return xmldoc;
}

The XmlWriter is writing a utf-8 byte-order mark to the stream. Encoding.UTF8.GetString doesn't account for this (since it's only supposed to occur in files) so the first character of the string becomes an invalid, unprintable character, which is what XmlDocument.LoadXml chokes on.
EDIT: Since you said you want to create an XmlDocument so you can reuse it, I recommend one of the following:
If using .Net 3.5 or newer, use XDocument which is much easier to use (I recommend this).
Create the XmlDocument directly by constructing nodes and adding them to the tree.
Create the XmlDocument directly from the writer by using XPathNavigator (XmlWriter writer = doc.CreateNavigator.AppendChild())
Note that you can't easily add insignificant whitespace to an XmlDocument. Using XDocument and writing it to the output using doc.Save(Response.Output) is by far the easiest option if you want to have nicely formatted output.

XmlWriter to Write to a String Instead of to a File

I have a WCF service that needs to return a string of XML. But it seems like the writer only wants to build up a file, not a string. I tried:
string nextXMLstring = "";
using (XmlWriter writer = XmlWriter.Create(nextXMLstring))
This generates an error saying nextXMLstring doesnt have a file path. It wants something like:
using (XmlWriter writer = XmlWriter.Create("nextXMLstring.xml"))
How can I build up my XML and then return it as a string??
Thanks!!

You need to create a StringWriter, and pass that to the XmlWriter.
The string overload of the XmlWriter.Create is for a filename.
E.g.
using (var sw = new StringWriter()) {
using (var xw = XmlWriter.Create(sw)) {
// Build Xml with xw.
}
return sw.ToString();
}

As Richard said, StringWriter is the way forward. There's one snag, however: by default, StringWriter will advertise itself as being in UTF-16. Usually XML is in UTF-8. You can fix this by subclassing StringWriter;
public class Utf8StringWriter : StringWriter
{
public override Encoding Encoding
{
get { return Encoding.UTF8; }
}
}
This will affect the declaration written by XmlWriter. Of course, if you then write the string out elsewhere in binary form, make sure you use an encoding which matches whichever encoding you fix for the StringWriter. (The above code always assumes UTF-8; it's trivial to make a more general version which accepts an encoding in the constructor.)
You'd then use:
using (TextWriter writer = new Utf8StringWriter())
{
using (XmlWriter xmlWriter = XmlWriter.Create(writer))
{
...
}
return writer.ToString();
}

I know this is old and answered, but here is another way to do it. Particularly if you don't want the UTF8 BOM at the start of your string and you want the text indented:
using (var ms = new MemoryStream())
using (var x = new XmlTextWriter(ms, new UTF8Encoding(false))
   { Formatting = Formatting.Indented })
{
  // ...
  return Encoding.UTF8.GetString(ms.ToArray());
}

Use StringBuilder:
var sb = new StringBuilder();
using (XmlWriter xmlWriter = XmlWriter.Create(sb))
{
...
}
return sb.ToString();

Guys don't forget to call xmlWriter.Close() and xmlWriter.Dispose() or else your string won't finish creating. It will just be an empty string

Well I think the simplest and fastest solution here would be just to:
StringBuilder sb = new StringBuilder();
using (var writer = XmlWriter.Create(sb, settings))
{
... // Whatever code you have/need :)
sb = sb.Replace("encoding=\"utf-16\"", "encoding=\"utf-8\""); //Or whatever uft you want/use.
//Before you finally save it:
File.WriteAllText("path\\dataName.xml", sb.ToString());
}

Make xml more readable

Is there any way to take an xml string in .net and make it easyer to read?
what i mean is can i convert this:
<element1><element2>some data</element2></element1>
to this:
<element1>
<element2>
some data
</element2>
</element1>
is there any built in class for this? as sql server 2005 seems to remove all formatting on xml to save space or some thing...

If you're using .NET 3.5, you can load it as an XDocument and then just call ToString() which will indent it appropriately. For example:
using System;
using System.Xml.Linq;
public class Test
{
static void Main()
{
string xml = "<element1><element2>some data</element2></element1>";
XDocument doc = XDocument.Parse(xml);
xml = doc.ToString();
Console.WriteLine(xml);
}
}
Result:
<element1>
<element2>some data</element2>
</element1>
If you're writing it to a file or other stream, then XDocument.Save will (by default) indent it too.
(I believe XElement has all the same features, if you don't really need an XDocument.)

How do you save / write the XML back to a file ?
You can create an XmlWriter and pass it an XmlWriterSettings instance, where you set the Indent property to true:
XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;
XmlWriter writer = XmlWriter.Create (outputStream, settings);

You can load the string into an XDocument object and save it to a string again:
XDocument doc = XDocument.Load(new StringReader(xmlString));
StringWriter writer = new StringWriter();
doc.Save(writer);
string readable = writer.ToString();
That will give you the xml formatted this way:
<?xml version="1.0" encoding="utf-16"?>
<element1>
<element2>some data</element2>
</element1>

Have a look at
XmlWriterSettings
http://msdn.microsoft.com/en-us/library/system.xml.xmlwritersettings.aspx
you can define Indent and IndentChars

First of all, you have tagged C# and VB.NET both. So my answer will be for both of them.
You can define function which get XML string as a parameter in type of String.
Let's say;
You created a function as :
[VB]
Private Function PrettyXML(XMLString As String) As String
Dim sw As New StringWriter()
Dim xw As New XMLWriter(sw)
xw.Formatiing = Formatting.Indented
xw.Indentation = 4
Dim doc As New XMLDocument
doc.LoadXML(XMLString)
doc.Save(xw)
Return sw.ToString()
End Function
Then you can simpyl call this function as:
Dim myXML As String = "<element1><element2>some data</element2></element1>"
Dim myPrettyXML As String
myPrettyXML = PrettyXML(myPrettyXML)
[C#]
Private String PrettyXML(string XMLString)
{
StringWriter sw = new StringWriter();
XMLTextWriter xw = new XmlTextWriter(sw);
xw.Formatiing = Formatting.Indented;
xw.Indentation = 4;
XmlDocument doc = new XmlDocument();
doc.Save(xm);
return sw.ToString();
}
Then you can simply call this function as:
string myXML = "<element1><element2>some data</element2></element1>";
string myPrettyXML = "";
myPrettyXML = PrettyXML(myPrettyXML);
NOTE: I have not tried C# version, but it should work.
Hope this helps..

Creating an XML Element object from an XML Writer in C#

I'm writing a Windows service in C#. I've got an XmlWriter which is contains the output of an XSLT transformation. I need to get the XML into an XMLElement object to pass to a web service.
What is the best way to do this?

You do not need an intermediate string, you can create an XmlWriter that writes directly into an XmlNode:
XmlDocument doc = new XmlDocument();
using (XmlWriter xw = doc.CreateNavigator().AppendChild()) {
// Write to `xw` here.
// Nodes written to `xw` will not appear in the document
// until `xw` is closed/disposed.
}
and pass xw as the output of the transform.
NB. Some parts of the xsl:output will be ignored (e.g. encoding) because the XmlDocument will use its own settings.

Well, an XmlWriter doesn't contain the output; typically, you have a backing object (maybe a StringBuilder or MemoryStream) that is the dumping place. In this case, StringBuilder is probably the most efficient... perhaps something like:
StringBuilder sb = new StringBuilder();
using (XmlWriter writer = XmlWriter.Create(sb))
{
// TODO write to writer via xslt
}
string xml = sb.ToString();
XmlDocument doc = new XmlDocument();
doc.LoadXml(xml);
XmlElement el = doc.DocumentElement;

If you provide a writer, you provide a repository where an output generator is transferring data, thus the replay of Richard is good, you don't really need a string builder to send data from a reader to an XmlDocument!