Enumeration: Returning the "next" item, round robin-style

[=?Utf-8?B?aGVyYmVydA==?=]

how do I code generic functions to return the next item in an enumeration
a) sorted by name, b) sorted by value c) sorted by declaration
in a round-robin style ?

for example the enum is
Enum Colors
Red = 5
Green = 7
Blue = 16
Yellow = 2
End Enum 'Colors

and the generic functions allow me to code:

Dim next as Colors = GetNextEnumItem ByName(colors, colors.green) 'returns
Colors.Red

Dim next as Colors = GetNextEnumItem ByValue(colors, colors.green) 'returns
Colors.Blue

Dim next as Colors = GetNextEnumItem (colors, colors.yellow) 'returns
Colors.red

I tried
Private Function GetNextEnumValu e(Of T)(ByVal start As T) As T
'get the next (round-robin style) value of an enumeration
Dim enumvalues() As String = [Enum].GetValues(GetT ype(Colors)) 'get
all enum values
Dim index As Integer = Array.IndexOf(e numvalues, start) 'find the
index of the start value
Dim target As Integer = (index + 1) Mod enumvalues.Leng th 'this is
the index of the "next" value
Return CType([Enum].Parse(T.GetTyp e, "Red"), T) '*** THIS T.GetType
FAILS ***
End Function

thank you very much. herbert

[=?Utf-8?B?UGV0ZXIgUml0Y2hpZSBbQyMgTVZQXQ==?=]

How about:
Private Shared Function GetNextEnumValu e(Of T As { Structure, IComparable
})(ByVal currentValue As T, ByRef nextValue As T) As Boolean
If Not TypeOf currentValue Is Enum Then
Throw New ArgumentExcepti on("Not Enum", "currentVal ue")
End If
Dim values As T() = TryCast(Enum.Ge tValues(GetType (T)),T())
If (Not values Is Nothing) Then
Dim i As Integer = 0
Do While (i < (values.Length - 1))
If (values(i).Comp areTo(currentVa lue) = 0) Then
nextValue = values((i + 1))
Return True
End If
i += 1
Loop
End If
Return False
End Function
--
Browse http://connect.microsoft.com/VisualStudio/feedback/ and vote.
http://www.peterRitchie.com/blog/
Microsoft MVP, Visual Developer - Visual C#
"herbert" wrote:

how do I code generic functions to return the next item in an enumeration
a) sorted by name, b) sorted by value c) sorted by declaration
in a round-robin style ?

for example the enum is
Enum Colors
Red = 5
Green = 7
Blue = 16
Yellow = 2
End Enum 'Colors

and the generic functions allow me to code:

Dim next as Colors = GetNextEnumItem ByName(colors, colors.green) 'returns
Colors.Red

Dim next as Colors = GetNextEnumItem ByValue(colors, colors.green) 'returns
Colors.Blue

Dim next as Colors = GetNextEnumItem (colors, colors.yellow) 'returns
Colors.red

I tried
Private Function GetNextEnumValu e(Of T)(ByVal start As T) As T
'get the next (round-robin style) value of an enumeration
Dim enumvalues() As String = [Enum].GetValues(GetT ype(Colors)) 'get
all enum values
Dim index As Integer = Array.IndexOf(e numvalues, start) 'find the
index of the start value
Dim target As Integer = (index + 1) Mod enumvalues.Leng th 'this is
the index of the "next" value
Return CType([Enum].Parse(T.GetTyp e, "Red"), T) '*** THIS T.GetType
FAILS ***
End Function

thank you very much. herbert

[=?Utf-8?B?aGVyYmVydA==?=]

Thank you, Peter.
This is my solution for all the VB.NET fans out there:
Private Function GetNextEnum(Of T)(ByVal start As T) As T
'get the next (round-robin style) value of an enumeration; the
sequence is as defined in the enumeration
Dim enumValues() As T = [Enum].GetValues(GetT ype(Colors)) 'get all
enum values
Dim index As Integer = Array.IndexOf(e numValues, start) 'find the
index of the start value
Dim target As Integer = (index + 1) Mod enumValues.Leng th 'this is
the index of the "next" value
Return enumValues(targ et)
End Function

Private Function GetNextEnumByVa lue(Of T)(ByVal start As T) As T
'get the next (round-robin style) value of an enumeration; the
sequence is defined by the values of the num items
Dim enumValues() As T = [Enum].GetValues(GetT ype(Colors)) 'get all
enum values
Array.Sort(enum Values) 'sort
the array
Dim index As Integer = Array.IndexOf(e numValues, start) 'find the
index of the start value
Dim target As Integer = (index + 1) Mod enumValues.Leng th 'this is
the index of the "next" value
Return enumValues(targ et)
End Function

Private Function GetNextEnumByNa me(Of T)(ByVal start As T) As T
'get the next (round-robin style) value of an enumeration; the
sequence is as defined by the names of the enum items
Dim enumNames() As String = [Enum].GetNames(GetTy pe(Colors)) 'get
all names of the items in the enum
Array.Sort(enum Names) 'sort the array of enum names by name
'find the index of the start value
Dim index As Integer = Array.IndexOf(e numNames, start.ToString)
'get the next item in the array
Dim targetIndex As Integer = (index + 1) Mod enumNames.Lengt h 'this
is the index of the "next" value
Return [Enum].Parse(GetType( T), enumNames(targe tIndex))
End Function