Appendix N : Useful Exception Classes

When your program throws an exception, it’s easy enough to use a Try Catch block to catch the exception and examine it to determine its class. When you want to throw your own exception, however, you must know what exception classes are available so that you can pick the right one.

For more information on error handling, see Chapter 8 and Appendix F.

Standard Exception Classes

The following table lists some of the most useful exception classes in Visual Basic .NET. You can raise one of these when you need to throw an error.

Open table as spreadsheet

Class	Purpose
AmbiguousMatchException	The program could not figure out which overloaded object method to use.
ApplicationException	This is the ancestor class for all nonfatal application errors. When you build custom exception classes, you should inherit from this class, or from one of its descendants.
ArgumentException	An argument is invalid.
ArgumentNullException	An argument that cannot be Nothing has value Nothing.
ArgumentOutOfRangeException	An argument is out of its allowed range.
ArithmeticException	An arithmetic, casting, or conversion operation has occurred.
ArrayTypeMismatchException	The program tried to store the wrong type of item in an array.
ConfigurationException	A configuration setting is invalid.
ConstraintException	A data operation violates a database constraint.
DataException	The ancestor class for ADO.NET exception classes.
DirectoryNotFoundException	A needed directory is missing.
DivideByZeroException	The program tried to divide by zero.
DuplicateNameException	An ADO.NET operation encountered a duplicate name (for example, it tried to create a second table with the same name).
EvaluateException	Occurs when a DataColumn’s Expression property cannot be evaluated.
FieldAccessException	The program tried to access a class property improperly.
FormatException	An argument’s format doesn’t match its required format.
IndexOutofRangeException	The program tried to access an item outside of the bounds of an array or other container.
InvalidCastException	The program tried to make an invalid conversion. For example, Integer.Parse(“oops”).
InvalidOperationException	The operation is not currently allowed.
IOException	The ancestor class for input/output (I/O) exception classes. A generic I/O error occurred.
EndOfStreamException	A stream reached its end.
FileLoadException	Error loading a file.
FileNotFoundException	Error finding a file.
InternalBufferOverflowException	An internal buffer overflowed.
MemberAccessException	The program tried to access a class member improperly.
MethodAccessException	The program tried to access a class method improperly.
MissingFieldException	The program tried to access a class property that doesn’t exist.
MissingMemberException	The program tried to access a class member that doesn’t exist.
MissingMethodException	The program tried to access a class method that doesn’t exist.
NotFiniteNumberException	A floating-point number is PositiveInfinity, NegativeInfinity, or NaN (Not a Number). You can get these values from the floating-point classes (as in Single.Nan or Double.PositiveInfinity).
NotImplementedException	The requested operation is not implemented.
NotSupportedException	The requested operation is not supported. For example, the program might be asking a routine to modify data that was opened as read-only.
NullReferenceException	The program tried to use an object reference that is Nothing.
OutOfMemoryException	There isn’t enough memory. Note that sometimes a program cannot recover from an OutOfMemoryException because it doesn’t have enough memory to do anything useful. This exception is most useful if you can predict beforehand that you will run out of memory before you actually use up all of the memory and crash the program. For example, if the user wants to generate a really huge data set, you may be able to predict how much memory the program will need, see if it is available, and throw this error without actually allocating the data set.
OverflowException	An arithmetic, casting, or conversion operation created an overflow. For example, the program tried to assign a large Integer value to a Byte variable.
PolicyException RankException	Policy prevents the code from running. A routine is trying to use an array with the wrong number of dimensions.
ReadOnlyException	The program tried to modify read-only data.
SecurityException	A security violation occurred.
SyntaxErrorException	A DataColumn’s Expression property contains invalid syntax.
UnauthorizedAccessException	The system is denying access because of an I/O or security error.

Use the Throw statement to raise an exception. The following code throws a DivideByZeroException. It passes the exception class’s constructor a message describing the exception. In this case, the divide by zero exception occurred because the application did not have any employees defined. Notice that the message explains the reason for the exception, not the mere fact that a division by zero occurred.

  Throw New DivideByZeroException("No employees are defined.")