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Enum.IsDefined Method

Returns an indication whether a constant with a specified value exists in a specified enumeration.

Namespace:  System
Assemblies:   System.Runtime (in System.Runtime.dll)
  mscorlib (in mscorlib.dll)

'Declaration
Public Shared Function IsDefined ( _
	enumType As Type, _
	value As Object _
) As Boolean

Parameters

enumType
Type: System.Type

An enumeration type.

value
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.

ExceptionCondition
ArgumentNullException

enumType or value is Nothing.

ArgumentException

enumType is not an Enum.

-or-

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

-or-

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

InvalidOperationException

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. To determine whether multiple bit fields are set in an enumeration type that is tagged with the FlagsAttribute attribute, you can call the HasFlag method.

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").

<Flags> Public Enum Pets As Integer
   None = 0
   Dog = 1
   Cat = 2
   Bird = 4
   Rodent = 8
   Other = 16
End Enum 

Module Example
   Public Sub Main()
      Dim value As Pets = Pets.Dog Or Pets.Cat
      Console.WriteLine("{0:D} Exists: {1}", 
                        value, Pets.IsDefined(GetType(Pets), value))
      Dim name As String = value.ToString()
      Console.WriteLine("{0} Exists: {1}", 
                        name, Pets.IsDefined(GetType(Pets), name))
   End Sub 
End Module 
' The example displays the following output: 
'       3 Exists: False 
'       Dog, Cat Exists: False

You can determine whether multiple bit fields are set by calling the HasFlag method.

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.

<Flags> Public Enum PetType As Integer
   None = 0
   Dog = 1
   Cat = 2
   Rodent = 4
   Bird = 8
   Reptile = 16
   Other = 32
End Enum 

Module Example
   Public Sub Main()
      Dim value As Object 

      ' Call IsDefined with underlying integral value of member.
      value = 1
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      ' Call IsDefined with invalid underlying integral value.
      value = 64
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      ' Call IsDefined with string containing member name.
      value = "Rodent"
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      ' Call IsDefined with a variable of type PetType.
      value = PetType.Dog
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      value = PetType.Dog Or PetType.Cat
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      ' Call IsDefined with uppercase member name.      
      value = "None"
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      value = "NONE"
      Console.WriteLine("{0}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      ' Call IsDefined with combined value
      value = PetType.Dog Or PetType.Bird
      Console.WriteLine("{0:D}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
      value = value.ToString()
      Console.WriteLine("{0:D}: {1}", value, [Enum].IsDefined(GetType(PetType), value))
   End Sub 
End Module 
' The example displays the following output: 
'       1: True 
'       64: False  
'       Rodent: True 
'       Dog: True 
'       Dog, Cat: False 
'       None: True 
'       NONE: False 
'       9: False 
'       Dog, Bird: False

.NET Framework

Supported in: 4.6, 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

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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