If XmlException.SourceUri is read-only, what good is it?

Question

I have a couple places in my code where it throwing a new System.Xml.XmlException seems appropriate. I could just do

throw new XmlException("Your XML sucks go fix it then try again.");  

But I think it's better to take advantage whenever possible of members particular to the exception class (otherwise ya might as well throw a plain ol' Exception every time). SourceUri and LineNumber would be helpful, but they only have get methods, there's no way I can assign a value to them! There's only 3 constructor overloads and none of them have parameters for those members either; I can only initialize Message, nothing else.

There has got to be some way to populate those data members with values, otherwise why does XmlException bother with them?

I suppose I could make a new class that inherits XmlException and write a new constructor that initializes SourceUri etc. but still, there must be a way to just use XmlException. Right?

Answer 1

There is a constructor with the line number and line position. I can't see anything that takes SourceUri though...

I believe you can populate it using the serialization streaming context - but that would be pretty fragile.

I think it's best to regard it as something which is effectively only provided by system-thrown XmlExceptions. I don't think that makes it useless - just less flexible than it might be. (I suspect the vast majority of XmlExceptions that are thrown in the world are thrown by the system rather than by user code.)

Answer 2

I took a look using Reflector, and it would seem that only two constructors set the SourceUri. Those are the deserialization one, and a single internal constructor that sets everything, but all the public ones call that with the SourceUri set to null. Obviously none of those can be easily accessed. I would conclude that there is no good way to set the SourceUri property.

Answer 3

There is a constructor that takes a sourceUri parameter :

internal XmlException(string res, string[] args, string sourceUri)

But since it is internal, it can only be called inside the System.Xml assembly. Anyway, I don't think you should throw an XmlException yourself. This exception is typically thrown by the XML-related BCL classes. You should rather create your own exception and throw it instead.