Polymorphism/Serialization DataContractSerializer (VB.NET)

Imports System.IO
Imports System.Runtime.Serialization
Imports System.Collections.Generic
Imports System.ComponentModel

Module Module1

    Sub Main()
        'Create some objects
        Dim dObj() = New DrawingObject(3) {}

        dObj(0) = New Line(100, 100)
        dObj(1) = New Circle(50, 10, 10)
        dObj(2) = New Square(10, 10, 20, 20)
        dObj(3) = New DrawingObject()

        For Each drawObj As DrawingObject In dObj

            Select Case drawObj.GetType().Name
                Case "Line"
                    Console.WriteLine(String.Format("I'm a {0}", drawObj.Draw()))
                    Dim line As Line = DirectCast(drawObj, Line)
                Case "Circle"
                    Console.WriteLine(String.Format("I'm a {0}", drawObj.Draw()))
                    Dim circle As Circle = DirectCast(drawObj, Circle)
                Case "Square"
                    Dim square As Square = DirectCast(drawObj, Square)
                    Console.WriteLine(String.Format("I'm a {0}", drawObj.Draw()))
                Case Else
                    Console.WriteLine(String.Format("I'm just a {0}", drawObj.Draw()))
            End Select
            drawObj.Draw()
        Next

        ' Serialize
        Serialize(dObj)

        Dim deserializedList = New List(Of DrawingObject)()
        ' deserialize to a generic list
        deserializedList = Deserialize(Of List(Of DrawingObject))()

        For Each DrawingObject As DrawingObject In deserializedList

            Select Case DrawingObject.GetType().Name
                Case "Line"
                    Console.WriteLine(String.Format("I'm a {0}", DrawingObject.Draw()))
                    Dim line As Line = DirectCast(DrawingObject, Line)
                Case "Circle"
                    Console.WriteLine(String.Format("I'm a {0}", DrawingObject.Draw()))
                    Dim circle As Circle = DirectCast(DrawingObject, Circle)
                Case "Square"
                    Dim square As Square = DirectCast(DrawingObject, Square)
                    Console.WriteLine(String.Format("I'm a {0}", DrawingObject.Draw()))
                Case Else
                    Console.WriteLine(String.Format("I'm just a {0}", DrawingObject.Draw()))
            End Select
        Next

    End Sub

    Public Sub Serialize(Of T)(data As T)
        Try
            Using stream As New FileStream("data.xml", FileMode.Create)
                Dim serializer = New DataContractSerializer(GetType(T))

                serializer.WriteObject(stream, Data)
            End Using
        Catch ex As Exception
        End Try
    End Sub

    Private Function Deserialize(Of T)() As T
        ' Create an instance of T
        Dim ReturnListOfT = CreateInstance(Of T)()

        Try
            Using stream As New FileStream("data.xml", FileMode.Open)
                ' create DataContractSerializer
                Dim serializer = New DataContractSerializer(GetType(T))
                ' deserialize the collection (Employee) from file (stream)
                ReturnListOfT = DirectCast(serializer.ReadObject(stream), T)
            End Using
        Catch ex As Exception
        End Try

        Return DirectCast(ReturnListOfT, T)
    End Function

    ' function to create instance of T
    Private Function CreateInstance(Of T)() As T
        Return DirectCast(Activator.CreateInstance(GetType(T)), T)
    End Function

End Module

<KnownType(GetType(Line))>
<KnownType(GetType(Circle))>
<KnownType(GetType(Square))>
<DataContract>
Public Class DrawingObject

    Public Sub New()

    End Sub

    Public Overridable Function Draw() As String
        Return "generic drawing object."
    End Function
End Class

<DataContract>
Public Class Square
    Inherits DrawingObject

    Public Overrides Function Draw() As String
        Return "Circle."
    End Function

    Public Sub New()
    End Sub

    Public Sub New(x1 As Integer, y1 As Integer, x2 As Integer, y2 As Integer)
        Me.X1 = x1
        Me.Y1 = y1
        Me.X2 = x2
        Me.Y2 = y2
    End Sub

    <DataMember>
    Public Property X1 As Integer
    <DataMember>
    Public Property Y1 As Integer

    <DataMember>
    Public Property X2 As Integer
    <DataMember>
    Public Property Y2 As Integer
End Class

<DataContract>
Public Class Line
    Inherits DrawingObject

    Public Overrides Function Draw() As String
        Return "Line."
    End Function

    Public Sub New()
    End Sub

    Public Sub New(x As Integer, y As Integer)

        Me.X = x
        Me.Y = y
    End Sub

    <DataMember>
    Public Property X As Integer
    <DataMember>
    Public Property Y As Integer
End Class

<DataContract>
Public Class Circle
    Inherits DrawingObject

    Public Overrides Function Draw() As String
        Return "Circle."
    End Function

    Public Sub New()
    End Sub

    Public Sub New(radius As Integer, x As Integer, y As Integer)
        Me.Radius = radius
        Me.X = x
        Me.Y = y
    End Sub

    <DataMember>
    Public Property Radius As Integer
    <DataMember>
    Public Property X As Integer
    <DataMember>
    Public Property Y As Integer

End Class