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.