Custom Object data binding, polymorphism and inheritance

[Laura Rowley]

I'm hoping that someone out there can give me some guidance here, and I hope that I am explaining this properly.


Here is my scenerio:

I have a BaseData object that serves as an abstract object for all my business objects. Notice there is an overridable method on the object.

Public Class BaseData

		Dim msDataID As String
		Dim msDescription As String


        
		<DataMember()>
		Property DataID() As String
			Get
				DataID = msDataID
			End Get
			Set(ByVal value As String)
				msDataID = value
			End Set
		End Property

		Property Description() As String
			Get
				Description = msDescription
			End Get
			Set(ByVal value As String)
				msDescription = value
			End Set
		End Property

        	Public Overridable Function GetAllObjects() As BaseDataCollection

            		Dim colObjects As BaseDataCollection = Nothing

            		colObjects = (get data from data source)

            		Return colObjects
        	End Function

	

End Class

Here is the base Collection that servers as the abstract collection for all my business object collections:

Public Class BaseDataCollection
        Inherits BindingList(Of BaseData)
        Implements IComponent

#Region "IComponent Implementation"
        Private m_Site As ISite = Nothing
        Public Event Disposed(ByVal sender As Object, ByVal e As System.EventArgs) _
            Implements System.ComponentModel.IComponent.Disposed

        Protected Property Site() As System.ComponentModel.ISite Implements _
            System.ComponentModel.IComponent.Site
            Get
                Return m_Site
            End Get
            Set(ByVal Value As System.ComponentModel.ISite)
                m_Site = Value
            End Set
        End Property

        Public Sub Dispose() Implements System.IDisposable.Dispose
            Me.Items.Clear()
            RaiseEvent Disposed(Me, System.EventArgs.Empty)
        End Sub
#End Region

#Region "IBindingList Sorting Features"
        Private m_SupportsSorting As Boolean = True
        Private m_SortProperty As PropertyDescriptor
        Private m_SortDirection As ListSortDirection
        Private m_OriginalList As ArrayList

        Protected Overrides ReadOnly Property SupportsSortingCore() As Boolean
            Get
                Return m_SupportsSorting
            End Get
        End Property
        Protected Overrides ReadOnly Property SortDirectionCore() As System.ComponentModel.ListSortDirection
            Get
                Return m_SortDirection
            End Get
        End Property

        Protected Overrides ReadOnly Property SortPropertyCore() As System.ComponentModel.PropertyDescriptor
            Get
                Return m_SortProperty
            End Get
        End Property

        Protected Overrides ReadOnly Property IsSortedCore() As Boolean
            Get
                Return m_SortProperty Is Nothing
            End Get
        End Property

        Private Sub SaveList()
            m_OriginalList = New ArrayList(Me.Items)
        End Sub

        Private Sub ResetList(ByVal NewList As ArrayList)
            Me.ClearItems()
            For Each m_Student As BaseData In NewList
                Me.Add(m_Student)
            Next
        End Sub

        Private Sub DoSort()
            Dim m_Comparer As New BaseDataComparer(m_SortProperty, m_SortDirection)
            Dim m_SortList As New ArrayList(Me.Items)
            m_SortList.Sort(m_Comparer)
            ResetList(m_SortList)
        End Sub

        Protected Overrides Sub ApplySortCore(ByVal prop As System.ComponentModel.PropertyDescriptor, ByVal direction As System.ComponentModel.ListSortDirection)
            m_SortProperty = prop
            m_SortDirection = direction
            If (m_OriginalList Is Nothing) Then
                SaveList()
            End If
            DoSort()
        End Sub

        Protected Overrides Sub RemoveSortCore()
            ResetList(m_OriginalList)
            m_SortDirection = Nothing
            m_SortProperty = Nothing
        End Sub
#End Region



    End Class

Here is an example of a derived object that inherits BaseData:

 Public Class MyUser
        Inherits BaseData

        Dim msUserName As String
        Dim msPassword As String
        

        Public Property UserName As String
            Get
                Return msUserName
            End Get
            Set(ByVal value As String)
                msUserName = value
            End Set
        End Property


        Public Property Password As String
            Get
                Return msPassword
            End Get
            Set(ByVal value As String)
                msPassword = value
            End Set
        End Property



        Public Overrides Function GetAllObjects() As Collections.BaseDataCollection
            Dim GetParams As New stcReadFileParams
            Dim myProcessor As New MasterProcessor
            Dim sObjectRec As String = ""
            Dim colObject As Collections.MyUserCollection = Nothing

            GetParams.FileName = FileName
            GetParams.KeyWord = RN_USERS
            GetParams.Mode = MODE_INQUIRY

            If Not UVSession Is Nothing Then myProcessor.UVSession = UVSession

            sObjectRec = myProcessor.GetMaster(GetParams)

            If sObjectRec <> "" Then
                colObject = ParseRecordIntoObjects(sObjectRec)
            End If

            Return colObject
        End Function


    End Class

Here is an example of a derived collection:

    Public Class MyUserCollection
        Inherits BaseDataCollection

    End Class

When I try to databind the result from MyUser.GetAllOb jects to my gridView I am only seeing the BASEDATA object properties of DataID and Description. What am I doing wrong? I thought that the rules of polymorphism would strongly type the BindingList (of BaseData) in to BindingList (of MyUser) but that does not appear to be the case.

Any help would be greatly appreciated.