VB.NET: Get dynamically value of constants - vb.net

Question

If have got the following definitions of constants:
Protected Const Xsl As String = "Configuration.Xsl"
Protected Const Form As String = "Settings.Form"
Protected Const Ascx As String = "Implementation.Ascx"
...
To fill a dictionary I use this constants as keys:
MyDictionary.Add(Converter.Xsl, "Item 1")
MyDictionary.Add(Converter.Form, "Item 2")
MyDictionary.Add(Converter.Ascx, "Item 3")
...
Now I run throug a loop of XML files and extract the name of the root node:
Dim document As New XmlDocument
document.Load(File.FullName)
Dim rootName As String = document.DocumentElement.Name
The root name matchs with the name of the constant. To get the value of an item from the dictionary I can use something like this:
Select Case rootName.ToUpper
Case "Xsl".ToUpper
DictionaryValue = MyDictionary(Class.Xsl)
Case "Form".ToUpper
DictionaryValue = MyDictionary(Class.Form)
Case "Ascx".ToUpper
DictionaryValue = MyDictionary(Class.Ascx)
...
Case Else
End Select
If a constant is added or removed I also have to change the selection. Is there another way to get the value of a constant? Something like
DictionaryValue = MyDictionary(SomeFunctionToGetConstantValue(rootName))
Thanks for any response.

Answer 1

Try this:
For Each sKey As String In MyDictionary.Keys
If rootName.Equals(sKey, StringComparison.CurrentCultureIgnoreCase) Then
DictionaryValue = MyDictionary(sKey)
Exit For
End If
Next
At least it will reduce the amount of coding in the select case.

Answer 2

#Clara Onager
My solution I used was the following
Me.GetType.GetField(
"Xsl",
Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Static Or System.Reflection.BindingFlags.FlattenHierarchy
).GetValue(Nothing)

Answer 3

This is a bit of a whopper but I think it provides a pretty elegant solution overall. This is how it is used:
Public Class ConstantsExample
Public Sub UseConstant()
Dim value As String = Constants.Types(TypeA)
Dim category As String = Constants.Categories(General)
End Sub
End Class
As you can see the code where you use it is as short as it can be made. It does rely on a big pile of source code though:
Public Enum TypeCodes
<Description("Type A")> TypeA = 0
<Description("Type B")> TypeB
<Description("Type C")> TypeC
End Enum
Public Enum CategoryCodes
<Description("General")> General = 0
<Description("Specific")> Specific
<Description("Other")> Other
End Enum
Public NotInheritable Class Constants
#Region "Resources"
Private Shared myTypes As Dictionary(Of TypeCodes, ConstantItem) = Nothing
Public Shared ReadOnly Property Types() As Dictionary(Of TypeCodes, ConstantItem)
Get
If myTypes Is Nothing Then
myTypes = New Dictionary(Of TypeCodes, ConstantItem)
BuildTypes(myTypes)
End If
Return myTypes
End Get
End Property
Private Shared Sub BuildTypes(ByRef dict As Dictionary(Of TypeCodes, ConstantItem))
With dict
.Add(TypeCodes.TypeA, New ConstantItem(TypeCodes.TypeA.Description, "Type A are..."))
.Add(TypeCodes.TypeB, New ConstantItem(TypeCodes.TypeB.Description, "Type B are..."))
.Add(TypeCodes.TypeC, New ConstantItem(TypeCodes.TypeC.Description, "Type C are..."))
End With
End Sub
#End Region
#Region "Categories"
Private Shared myCategories As Dictionary(Of CategoryCodes, ConstantItem) = Nothing
Public Shared ReadOnly Property Categories() As Dictionary(Of CategoryCodes, ConstantItem)
Get
If myCategories Is Nothing Then
myCategories = New Dictionary(Of CategoryCodes, ConstantItem)
BuildCategories(myCategories)
End If
Return myCategories
End Get
End Property
Private Shared Sub BuildCategories(ByRef dict As Dictionary(Of CategoryCodes, ConstantItem))
With dict
.Add(CategoryCodes.General, New ConstantItem(CategoryCodes.General.Description, "General category"))
.Add(CategoryCodes.Specific, New ConstantItem(CategoryCodes.Specific.Description, "Specific category"))
.Add(CategoryCodes.Other, New ConstantItem(CategoryCodes.Other.Description, "Other category"))
End With
End Sub
#End Region
End Class
Public NotInheritable Class ConstantItem
#Region "Constructors"
''' <summary>
''' Default constructor.
''' </summary>
Public Sub New()
'Do nothing
End Sub
''' <summary>
''' Simple constructor.
''' </summary>
Sub New(value As String)
Me.Name = value
Me.Description = value
End Sub
''' <summary>
''' Proper constructor.
''' </summary>
Sub New(name As String, description As String)
Me.Name = name
Me.Description = description
End Sub
#End Region
Property Name As String
Property Description As String
''' <summary>
''' See http://stackoverflow.com/questions/293215/default-properties-in-vb-net
''' </summary>
Public Shared Widening Operator CType(value As String) As ConstantItem
Return New ConstantItem(value)
End Operator
''' <summary>
''' See http://stackoverflow.com/questions/293215/default-properties-in-vb-net
''' </summary>
Public Shared Widening Operator CType(value As ConstantItem) As String
Return value.Name
End Operator
End Class
Note the use of the Widening Operator to dispense with having to type .Item. If you'd rather not use the Widening Operator then simple comment that bit out and change Constants.Types(TypeA) to Constants.Types.Item(TypeA).
This is the Description Extension you may need:
Public Module Extensions
Private Enum SampleDescription
<Description("Item One")> ItemOne = 1
<Description("Item Two")> ItemTwo = 2
<Description("Item Three has a long description")> ItemThree = 3
End Enum
''' <summary>
''' This procedure gets the description attribute of an enum constant, if any. Otherwise it gets
''' the string name of the enum member.
''' </summary>
''' <param name="value"></param>
''' <returns></returns>
''' <remarks>Usage: myenum.Member.Description()
''' Add the Description attribute to each member of the enumeration.</remarks>
<Extension()> _
Public Function Description(ByVal value As [Enum]) As String
Dim fi As Reflection.FieldInfo = value.GetType().GetField(value.ToString())
Dim aattr() As DescriptionAttribute = DirectCast(fi.GetCustomAttributes(GetType(DescriptionAttribute), False), DescriptionAttribute())
If aattr.Length > 0 Then
Return aattr(0).Description
Else
Return value.ToString()
End If
End Function
End Module
And these are the Imports statements I used (the Assembly is called MyPatterns):
Imports System.ComponentModel
Imports MyPatterns.TypeCodes
Imports MyPatterns.CategoryCodes
Importing the two 'codes' allows you to do without the prefix for the Enum which shortens the code.