Enum.IsDefined Method

July 28, 2014

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

Namespace:  System
Assembly:  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 not an 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 is designed to determine 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.

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 Demo(outputBlock As System.Windows.Controls.TextBlock)
      Dim value As Object

      ' Call IsDefined with underlying integral value of member.
      value = 1
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      ' Call IsDefined with invalid underlying integral value.
      value = 64
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      ' Call IsDefined with string containing member name.
      value = "Rodent"
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      ' Call IsDefined with a variable of type PetType.
      value = PetType.Dog
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      value = PetType.Dog Or PetType.Cat
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      ' Call IsDefined with uppercase member name.      
      value = "None"
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf 
      value = "NONE"
      outputBlock.Text += String.Format("{0}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      ' Call IsDefined with combined value
      value = PetType.Dog Or PetType.Bird
      outputBlock.Text += String.Format("{0:D}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
      value = value.ToString()
      outputBlock.Text += String.Format("{0:D}: {1}", _
                          value, [Enum].IsDefined(GetType(PetType), value)) + vbCrLf
   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


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

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