I am trying to set the innerxml of a xmldoc but get the exception: Reference to undeclared entity
XmlDocument xmldoc = new XmlDocument();
string text = "Hello, I am text α – —"
xmldoc.InnerXml = "<p>" + text + "</p>";
This throws the exception: Reference to undeclared entity 'alpha'. Line 2, position 2..
How would I go about solving this problem?
XML, unlike HTML does not define entities (ie named references to UNICODE characters) so α — etc. are not translated to their corresponding character. You must use the numerical value instead. You can only use < and & in XML
If you want to create HTML, use an HtmlDocument instead.
The preceding answer is right. Another alternative is to link your html document to the DTD where those character entities are defined, and that is standard XHTML DTD definition. Your xml file should include the following declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
You could also set the InnerText to "Hello, I am text α – —", making the XmlDocument escape them automatically. I think.
In .Net, you can use the System.Xml.XmlConvert class:
string text = XmlConvert.EncodeName("Hello α");
Alternatively, you can declare the entities locally by putting the declarations between square brackets in a DOCTYPE declaration. Add the following header to your xml:
<!DOCTYPE documentElement[
<!ENTITY Alpha "Α">
<!ENTITY ndash "–">
<!ENTITY mdash "—">
]>
Do a google on "html character entities" for the entity definitions.
The use of a HtmlDocument wasn't suitable in my situation, our system had a custom XmlUrlResolver which we made use of for loading the xml.
//setup
public class CustomXmlResolver : XmlUrlResolver { /* ... */ }
String originalXml; //fetched xml with html entities in it
var doc = new XmlDocument();
doc.XmlResolver = new AdCastXmlResolver();
//making use of a transitional dtd
doc.LoadXml("<!DOCTYPE html SYSTEM \"xhtml1-transitional.dtd\" > " + originalXml);