CustomValiadtor in CustomConfigSection

Question

Hi,

I wrote a custom ConfigSection like this:

Public Class LoaderConfigSection
        Inherits AConfigSectionBase

        Private Shared _section As LoaderConfigSection

        Private Shared _instantiationLock As New ReaderWriterLockSlim

        Private Sub New()

        End Sub

        Public Shared Function getSection() As LoaderConfigSection
            Try
                _instantiationLock.EnterWriteLock()
                If _section Is Nothing Then
                    _section = CType(_config.GetSection("frameworkConfigGroup/loader"), LoaderConfigSection)

                    If _section Is Nothing Then
                        Throw New ConfigurationErrorsException("Section not found!!")
                    End If
                End If

                Return _section
            Catch ex As Exception
                Throw
            Finally
                _instantiationLock.ExitWriteLock()
            End Try
        End Function

        ' <ConfigurationProperty("Mode", DefaultValue:="singleAppDomain", IsRequired:=True), StringValueValidator("singleAppDomain;multipleAppdomains")> _

        '<ConfigurationProperty("Mode", DefaultValue:="singleAppDomain", IsRequired:=True)> _
        <ConfigurationProperty("Mode", DefaultValue:="singleAppDomain", IsRequired:=True), StringValueValidator("singleAppDomain;multipleAppdomains")> _
        Public Property Mode() As String

            Get
                Try
                    _lock.EnterReadLock()
                    Return (CType(Me("Mode"), String))
                Catch ex As Exception
                    Throw
                Finally
                    _lock.ExitReadLock()
                End Try
            End Get
            Set(ByVal value As String)
                Try
                    _lock.EnterWriteLock()
                    Me("Mode") = value
                Catch ex As Exception
                    Throw
                Finally
                    _lock.ExitWriteLock()
                End Try
            End Set
        End Property

    End Class
End Namespace

Within the section I try to use a custom validator object the StringValueValidator that looks like this:

<AttributeUsage(AttributeTargets.All)> _
    Public Class StringValueValidatorAttribute
        Inherits ConfigurationValidatorAttribute
        Private _validator As StringValueValidator

        Public Property ValidStrings() As String
            Get
                Return _validator.ValidStrings
            End Get
            Set(ByVal value As String)
                _validator.ValidStrings = value
            End Set
        End Property
        ''' <summary>
        ''' 
        ''' </summary>
        ''' <param name="validStrings">the valid strings seperated by ;</param>
        ''' <remarks></remarks>
        Public Sub New(ByVal validStrings As String)
            _validator = New StringValueValidator(validStrings)
        End Sub

        Public Function CanValidate(ByVal type As System.Type) As Boolean
            Return _validator.CanValidate(type)
        End Function

        Public Sub Validate(ByVal value As Object)
            _validator.Validate(value)
        End Sub

    End Class

But everytime I start the app, an exception occurs: Error when creating the ConfigurationSectionHandler.The value must not be NULL. Parametername:Type.

This exception only occurs, when I use the Stringvaluevalidator.

Thank you.

Harry

Answer 1

Your string validator class must derive from ConfigurationValidatorBase.  The CanValidate and Validate methods must be marked as overridable.  You must also implement the ValidatorInstance property on your validator attribute.  This property can return your created validator instance.

Public Class StringValueValidatorAttribute
   ...

   Public Overrides ReadOnly Property ValidatorInstance As ConfigurationValidatorBase
      Get
         Return _validator
      End Get
   End Property
End Class

Public Class StringValueValidator
   Inherits ConfigurationValidatorBase
 
   ...
End Class

Michael Taylor - 11/5/09
http://p3net.mvps.org

Answer 2

Thanks a lot that worked.

Answer 3

Thank you, Michael, for the sharing of the solution! :)

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Regards,
Jialiang Ge
MSDN Subscriber Support in Forum
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