Check well-formed XML without a try/catch?

Question

Does anyone know how I can check if a string contains well-formed XML without using something like XmlDocument.LoadXml() in a try/catch block? I've got input that may or may not be XML, and I want code that recognises that input may not be XML without relying on a try/catch, for both speed and on the general principle that non-exceptional circumstances shouldn't raise exceptions. I currently have code that does this;

private bool IsValidXML(string value)     {         try         {             // Check we actually have a value             if (string.IsNullOrEmpty(value) == false)             {                 // Try to load the value into a document                 XmlDocument xmlDoc = new XmlDocument();                  xmlDoc.LoadXml(value);                  // If we managed with no exception then this is valid XML!                 return true;             }             else             {                 // A blank value is not valid xml                 return false;             }         }         catch (System.Xml.XmlException)         {             return false;         }     } 

But it seems like something that shouldn't require the try/catch. The exception is causing merry hell during debugging because every time I check a string the debugger will break here, 'helping' me with my pesky problem.

Answer 1

I don't know a way of validating without the exception, but you can change the debugger settings to only break for XmlException if it's unhandled - that should solve your immediate issues, even if the code is still inelegant.

To do this, go to Debug / Exceptions... / Common Language Runtime Exceptions and find System.Xml.XmlException, then make sure only "User-unhandled" is ticked (not Thrown).

Answer 2

Steve,

We had an 3rd party that accidentally sometimes sent us JSON instead of XML. Here is what I implemented:

public static bool IsValidXml(string xmlString) {     Regex tagsWithData = new Regex("<\\w+>[^<]+</\\w+>");      //Light checking     if (string.IsNullOrEmpty(xmlString) || tagsWithData.IsMatch(xmlString) == false)     {         return false;     }      try     {         XmlDocument xmlDocument = new XmlDocument();         xmlDocument.LoadXml(xmlString);         return true;     }     catch (Exception e1)     {         return false;     } }  [TestMethod()] public void TestValidXml() {     string xml = "<result>true</result>";     Assert.IsTrue(Utility.IsValidXml(xml)); }  [TestMethod()] public void TestIsNotValidXml() {     string json = "{ \"result\": \"true\" }";     Assert.IsFalse(Utility.IsValidXml(json)); }