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Enum.IsDefined Method

Indicates whether a constant with a specified value exists in a specified enumeration.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

static member IsDefined : 
        enumType:Type * 
        value:Object -> bool 


Type: System.Type
The enumeration type to check.
Type: System.Object
The value or name of a constant in enumType.

Return Value

Type: System.Boolean
true if a constant in enumType has a value equal to value; otherwise, false.


enumType or value is a null reference (Nothing in Visual Basic).


enumType is not an Enum.


The type of value is an enumeration, but it is not an enumeration of type enumType.


The type of value is not an underlying type of enumType.


value is not type SByte, Int16, Int32, Int64, Byte, UInt16, UInt32, or UInt64, or String.

The value parameter can be any of the following:

  • Any member of type enumType.

  • A variable whose value is an enumeration member of type enumType.

  • The string representation of the name of an enumeration member. The characters in the string must have the same case as the enumeration member name.

  • A value of the underlying type of enumType.

If the constants in enumType define a set of bit fields and value contains the values, names, or underlying values of multiple bit fields, the IsDefined method returns false. In other words, for enumerations that define a set of bit fields, the method determines only whether a single bit field belongs to the enumeration.

Notes to Callers

If enumType is an enumeration that is defined by using the FlagsAttribute attribute, the method returns false if multiple bit fields in value are set but value does not correspond to a composite enumeration value, or if value is a string concatenation of the names of multiple bit flags. In the following example, a Pets enumeration is defined with the FlagsAttribute attribute. The IsDefined method returns false when you pass it an enumeration value that has two bit fields (Pets.Dog and Pets.Cat) set, and when you pass it the string representation of that enumeration value ("Dog, Cat").

No code example is currently available or this language may not be supported.

The following example defines an enumeration named PetType that consists of individual bit fields. It then calls the IsDefined method with possible underlying enumeration values, string names, and composite values that result from setting multiple bit fields.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.