When API methods encounter a non-fatal error, they throw an exception. Exceptions should be caught by Revit add-ins. The Revit API help file specifies exceptions that are typically encountered for specific methods. All Revit API methods throw a subclass of Autodesk.Revit.Exceptions.ApplicationException. These exceptions closely mirror standard .NET exceptions such as:
However, some of these subclasses are unique to Revit:
In addition, there is a special exception type called InternalException, which represents a failure path which was not anticipated. Exceptions of this type carry extra diagnostic information which can be passed back to Autodesk for diagnosis.