CODEWITHSUNDEEP
c#.netxmlexception
Chris Ballance
Chris Ballance

Reputation: 34337

How to check for valid xml in string input before calling .LoadXml()

I would much prefer to do this without catching an exception in LoadXml() and using this results as part of my logic. Any ideas for a solution that doesn't involve manually parsing the xml myself? I think VB has a return value of false for this function instead of throwing an XmlException. Xml input is provided from the user. Thanks much!

if (!loaded)
{
     this.m_xTableStructure = new XmlDocument();
     try
     {
          this.m_xTableStructure.LoadXml(input);
          loaded = true;
     }
     catch
     {
          loaded = false;
     }
}

Upvotes: 45

Views: 107004

Answers (5)

Dan
Dan

Reputation: 889

I was unable to get XmlValidatingReader & ValidationEventHandler to work. The XmlException is still thrown for incorrectly formed xml. I verified this by viewing the methods with reflector.

I indeed need to validate 100s of short XHTML fragments per second. 

public static bool IsValidXhtml(this string text)
{
   bool errored = false;
   var reader = new XmlValidatingReader(text, XmlNodeType.Element, new XmlParserContext(null, new XmlNamespaceManager(new NameTable()), null, XmlSpace.None));
   reader.ValidationEventHandler += ((sender, e) => { errored = e.Severity == System.Xml.Schema.XmlSeverityType.Error; });

   while (reader.Read()) { ; }
   reader.Close();
   return !errored;
}

XmlParserContext did not work either.

Anyone succeed with a regex?

Upvotes: 8

Rasmus Faber
Rasmus Faber

Reputation: 49619

Just catch the exception. The small overhead from catching an exception drowns compared to parsing the XML.

If you want the function (for stylistic reasons, not for performance), implement it yourself:

public class MyXmlDocument: XmlDocument
{
  bool TryParseXml(string xml){
    try{
      ParseXml(xml);
      return true;
    }catch(XmlException e){
      return false;
    }
 }

Upvotes: 69

Martin Marconcini
Martin Marconcini

Reputation: 27226

If catching is too much for you, then you might want to validate the XML beforehand, using an XML Schema, to make sure that the XML is ok, But that will probably be worse than catching.

Upvotes: 3

Martin Marconcini
Martin Marconcini

Reputation: 27226

AS already been said, I'd rather catch the exception, but using XmlParserContext, you could try to parse "manually" and intercept any anomaly; however, unless you're parsing 100 xml fragments per second, why not catching the exception?

Upvotes: 1

Sunny Milenov
Sunny Milenov

Reputation: 22310

Using a XmlValidatingReader will prevent the exceptions, if you provide your own ValidationEventHandler.

Upvotes: 11

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