Recipe 5.3 Choosing when to Throw a Particular Exception

Problem

There are many exceptions to choose from in the FCL. You need an easily accessible list of these exceptions that indicates when and where to use them. By throwing exceptions in a consistent manner (e.g., throwing an IndexOutOfRangeException when an array index is greater than the length of the array), you and others on your team will be able to debug problems more easily.

Solution

Use the list of exceptions and their definitions in Table 5-1 to determine which exception to employ when throwing or catching exceptions.

Discussion

Table 5-1. The built-in exception types

Exception name	Derives from	Description
System.ApplicationException	Exception	Use this class as the base class to user-defined exceptions; a more derived exception should be thrown.
System.ArgumentNullException	ArgumentException	Thrown when a parameter value for a method is null and null is not allowed.
System.ArgumentOutOfRangeException	ArgumentException	Thrown when a parameter value for a method is out of the range of expected values.
System.ArrayTypeMismatchException	SystemException	Thrown when an incompatible data type is assigned to an element in an array.
System.Runtime.InteropServices.COMException	ExternalException	Thrown when an unknown HRESULT is returned from a COM object.
System.Configuration.ConfigurationException	SystemException	Thrown when an invalid configuration setting is encountered.
System.Reflection.CustomAttributeFormatException	FormatException	Thrown when a custom attribute format is incorrect.
System.IO.DirectoryNotFoundException	IOException	Thrown when a file or directory cannot be found.
System.Exception	Object	Base class of all exceptions; you should always throw a more derived exception.
System.FormatException	SystemException	Thrown when an invalid format parameter is passed to a method.
System.IndexOutOfRangeException	SystemException	Thrown when you attempt to access an array element with an index value outside the valid range for that array.
System.Configuration.Install.InstallException	SystemException	Thrown during software installation when an error is encountered during uninstall, committing of data, or rolling back of data.
System.ComponentModel.InvalidEnumArgumentException	ArgumentException	Thrown when an invalid enumeration value is passed to a method.
System.InvalidOperationException	SystemException	Thrown when a method is called while the object it resides in is in a state that makes it illegal to call this method.
System.IO.IOException	SystemException	Thrown when a general I/O exception occurs; you should throw a more derived exception.
System.MemberAccessException	SystemException	Thrown when a general error occurs while using a class member; you should throw a more derived exception.
System.MethodAccessException	MemberAccessException	Thrown when a general error occurs while using a method member.
System.NotFiniteNumberException	ArithmeticException	Thrown when a double or single data type is expected to have a finite number and instead it contains NaN, +infinity, or - infinity.
System.NotImplementedException	SystemException	Thrown when a member is accessed that is not yet implemented.
System.NotSupportedException	SystemException	Thrown when a member is accessed that is not yet supported.
System.NullReferenceException	SystemException	Thrown when a reference set to null is used.
System.ObjectDisposedException	InvalidOperation-Exception	Thrown when a disposed object is accessed.
System.ServiceProcess.TimeoutException	SystemException	Thrown when a service times out.
System.ComponentModel.WarningException	SystemException	Thrown when a warning message needs to be displayed. This exception does not imply a serious failure of the application or system.
System.Net.WebException	InvalidOperation-Exception	Thrown when a pluggable protocol causes an error.
System.Xml.XmlException	SystemException	Thrown due to a general error in the XML.

See Also

See the "Exception Class" topic in the MSDN documentation; also see the classes that derive from the Exception class.