Visual Basic .NET Language

Enum

Enum definition

An enum is a set of logically related constants.

Enum Size
    Small
    Medium
    Large
End Enum

Public Sub Order(shirtSize As Size)
    Select Case shirtSize
        Case Size.Small
            ' ...
        Case Size.Medium
            ' ...
        Case Size.Large
            ' ...
    End Select
End Sub

Member initialization

Each of the enum members may be initialized with a value. If a value is not specified for a member, by default it’s initialized to 0 (if it’s the first member in the member list) or to a value greater by 1 than the value of the preceding member.

Module Module1

    Enum Size
        Small
        Medium = 3
        Large
    End Enum

    Sub Main()
        Console.WriteLine(Size.Small)    ' prints 0
        Console.WriteLine(Size.Medium)   ' prints 3
        Console.WriteLine(Size.Large)    ' prints 4

        ' Waits until user presses any key
        Console.ReadKey()
    End Sub

End Module

The Flags attribute

With the <Flags> attribute, the enum becomes a set of flags. This attribute enables assigning multiple values to an enum variable. The members of a flags enum should be initialized with powers of 2 (1, 2, 4, 8…).

Module Module1

    <Flags>
    Enum Material
        Wood = 1
        Plastic = 2
        Metal = 4
        Stone = 8
    End Enum

    Sub Main()
        Dim houseMaterials As Material = Material.Wood Or Material.Stone
        Dim carMaterials as Material = Material.Plastic Or Material.Metal
        Dim knifeMaterials as Material = Material.Metal

        Console.WriteLine(houseMaterials.ToString()) 'Prints "Wood, Stone"
        Console.WriteLine(CType(carMaterials, Integer)) 'Prints 6
    End Sub

End Module

HasFlag()

The HasFlag() method can be used to check if a flag is set.

Module Module1

    <Flags>
    Enum Material
        Wood = 1
        Plastic = 2
        Metal = 4
        Stone = 8
    End Enum

    Sub Main()
        Dim houseMaterials As Material = Material.Wood Or Material.Stone

        If houseMaterials.HasFlag(Material.Stone) Then
            Console.WriteLine("the house is made of stone")
        Else
            Console.WriteLine("the house is not made of stone")
        End If
    End Sub

End Module

For more information about the Flags-attribute and how it should be used see the official Microsoft documentation.

String parsing

An Enum instance can be created by parsing a string representation of the Enum.

Module Module1

    Enum Size
        Small
        Medium
        Large
    End Enum

    Sub Main()
        Dim shirtSize As Size =  DirectCast([Enum].Parse(GetType(Size), "Medium"), Size)

        ' Prints 'Medium'
        Console.WriteLine(shirtSize.ToString())

        ' Waits until user presses any key
        Console.ReadKey()
    End Sub

End Module

See also: https://stackoverflow.com/questions/852141/parse-a-string-to-an-enum-value-in-vb-net/852156#852156

GetNames()

Returns the names of constants in the specified Enum as a string array:

Module Module1

  Enum Size
    Small
    Medium
    Large
  End Enum

  Sub Main()
    Dim sizes = [Enum].GetNames(GetType(Size))

    For Each size In sizes
      Console.WriteLine(size)
      Next
  End Sub

End Module

Output:

Small

Medium

Large

GetValues()

’ This method is useful for iterating Enum values ’

Enum Animal
    Dog = 1
    Cat = 2
    Frog = 4
End Enum

Dim Animals = [Enum].GetValues(GetType(Animal))

For Each animal in Animals
    Console.WriteLine(animal)
Next

Prints:

1

2

4

ToString()

The ToString method on an enum returns the string name of the enumeration. For instance:

Module Module1
    Enum Size
        Small
        Medium
        Large
    End Enum

    Sub Main()
        Dim shirtSize As Size = Size.Medium
        Dim output As String = shirtSize.ToString()
        Console.WriteLine(output)  ' Writes "Medium"
    End Sub
End Module

If, however, the string representation of the actual integer value of the enum is desired, you can cast the enum to an Integer and then call ToString:

Dim shirtSize As Size = Size.Medium
Dim output As String = CInt(shirtSize).ToString()
Console.WriteLine(output)  ' Writes "1"

Determine whether a Enum has FlagsAttribute specified or not

The next example can be used to determine whether a enumeration has the FlagsAttribute specified. The methodology used is based on Reflection.

This example will give a True result:

Dim enu As [Enum] = New FileAttributes()
Dim hasFlags As Boolean = enu.GetType().GetCustomAttributes(GetType(FlagsAttribute), inherit:=False).Any()
Console.WriteLine("{0} Enum has FlagsAttribute?: {1}", enu.GetType().Name, hasFlags)

This example will give a False result:

Dim enu As [Enum] = New ConsoleColor()
Dim hasFlags As Boolean = enu.GetType().GetCustomAttributes(GetType(FlagsAttribute), inherit:=False).Any()
Console.WriteLine("{0} Enum has FlagsAttribute?: {1}", enu.GetType().Name, hasFlags)

We can design a generic usage extension method like this one:

<DebuggerStepThrough>
<Extension>
<EditorBrowsable(EditorBrowsableState.Always)>
Public Function HasFlagsAttribute(ByVal sender As [Enum]) As Boolean
    Return sender.GetType().GetCustomAttributes(GetType(FlagsAttribute), inherit:=False).Any()
End Function

Usage Example:

Dim result As Boolean = (New FileAttributes).HasFlagsAttribute()

For-each flag (flag iteration)

In some very specific scenarios we would feel the need to perform a specific action for each flag of the source enumeration.

We can write a simple Generic extension method to realize this task.

<DebuggerStepThrough>
<Extension>
<EditorBrowsable(EditorBrowsableState.Always)>
Public Sub ForEachFlag(Of T)(ByVal sender As [Enum],
                             ByVal action As Action(Of T))

    For Each flag As T In sender.Flags(Of T)
        action.Invoke(flag)
    Next flag

End Sub

Usage Example:

Dim flags As FileAttributes = (FileAttributes.ReadOnly Or FileAttributes.Hidden)
    
flags.ForEachFlag(Of FileAttributes)(
      Sub(ByVal x As FileAttributes)
          Console.WriteLine(x.ToString())
      End Sub)

Determine the amount of flags in a flag combination

The next example is intended to count the amount of flags in the specified flag combination.

The example is provided as a extension method:

<DebuggerStepThrough>
<Extension>
<EditorBrowsable(EditorBrowsableState.Always)>
Public Function CountFlags(ByVal sender As [Enum]) As Integer
    Return sender.ToString().Split(","c).Count()
End Function

Usage Example:

Dim flags As FileAttributes = (FileAttributes.Archive Or FileAttributes.Compressed)
Dim count As Integer = flags.CountFlags()
Console.WriteLine(count)

Find the nearest value in a Enum

The next code illustrates how to find the nearest value of a Enum.

First we define this Enum that will serve to specify search criteria (search direction)

Public Enum EnumFindDirection As Integer
    Nearest = 0
    Less = 1
    LessOrEqual = 2
    Greater = 3
    GreaterOrEqual = 4
End Enum

And now we implement the search algorithm:

<DebuggerStepThrough>
Public Shared Function FindNearestEnumValue(Of T)(ByVal value As Long,
                                                  ByVal direction As EnumFindDirection) As T

    Select Case direction

        Case EnumFindDirection.Nearest
            Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                    Order By Math.Abs(value - Convert.ToInt64(enumValue))
                    ).FirstOrDefault

        Case EnumFindDirection.Less
            If value < Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).First) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).FirstOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) < value
                        ).LastOrDefault
            End If

        Case EnumFindDirection.LessOrEqual
            If value < Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).First) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).FirstOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) <= value
                        ).LastOrDefault
            End If

        Case EnumFindDirection.Greater
            If value > Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).Last) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).LastOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) > value
                        ).FirstOrDefault
            End If

        Case EnumFindDirection.GreaterOrEqual
            If value > Convert.ToInt64([Enum].GetValues(GetType(T)).Cast(Of T).Last) Then
                Return [Enum].GetValues(GetType(T)).Cast(Of T).LastOrDefault

            Else
                Return (From enumValue As T In [Enum].GetValues(GetType(T)).Cast(Of T)()
                        Where Convert.ToInt64(enumValue) >= value
                        ).FirstOrDefault
            End If

    End Select

End Function

Usage Example:

Public Enum Bitrate As Integer
    Kbps128 = 128
    Kbps192 = 192
    Kbps256 = 256
    Kbps320 = 320
End Enum

Dim nearestValue As Bitrate = FindNearestEnumValue(Of Bitrate)(224, EnumFindDirection.GreaterOrEqual)
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