[2005] Deserialization and Late Binding

[ctbny]

I have an object that I am deserializing. The object is a Generic.List and it could contain one of two different objects, so how do I find what objects are in the List so that I can use directcast. I'm tying to find a solution that doesn't use late binding. I think the solution involves reflection but I don't know how to do it.

[Tom Sawyer]

If you use xml serialization, then you can just take a look at the nodes and see what's in there. Here's a little code snippet I whipped up to show how it could be done. Each list seems to get serialized with a root node of <ArrayOf{Object}>, so you can just pull that out and grab the type based on what it is.

    Private Sub btnDeserialize_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDeserialize.Click

        Dim lst1 As New List(Of String)
        lst1.Add("Hello")
        lst1.Add("Goodbye")

        SerializeXML(lst1, "c:\string.xml")

        Dim lst2 As New List(Of Integer)
        lst2.Add(4)
        lst2.Add(6)

        SerializeXML(lst2, "c:\integer.xml")

        Dim lst3 As New List(Of Person)
        Dim p1 As New Person
        p1.FirstName = "Peter"
        p1.LastName = "Higgins"
        Dim p2 As New Person
        p2.FirstName = "Tom"
        p2.LastName = "Sawyer"
        lst3.Add(p1)
        lst3.Add(p2)

        SerializeXML(lst3, "c:\person.xml")

        MessageBox.Show(DeserializeXML("c:\string.xml"))
        MessageBox.Show(DeserializeXML("c:\integer.xml"))
        MessageBox.Show(DeserializeXML("c:\person.xml"))

    End Sub

    Private Sub SerializeXML(ByVal obj As Object, ByVal fileName As String)

        Dim serializer As New Xml.Serialization.XmlSerializer(obj.GetType)
        Dim memStrm As New System.IO.MemoryStream
        serializer.Serialize(memStrm, obj)
        memStrm.Position = 0
        Dim doc As New XmlDocument()
        doc.Load(memStrm)
        doc.Save(fileName)
        memStrm.Close()

    End Sub

    Private Function DeserializeXML(ByVal fileName As String) As String

        Dim doc As New XmlDocument
        doc.Load(fileName)

        Return doc.DocumentElement.Name.Replace("ArrayOf", "")

    End Function

[kleinma]

if it is a generic list of whatever, then calling gettype on one of the lists elements will give you the the specific type of the elements inside...

something like this:

    Public Function GetGenericTypeString() As String
        If _GenericList.Item(0).GetType.Equals(GetType(System.Int32)) Then
            Return "INTEGER"
        ElseIf _GenericList.Item(0).GetType.Equals(GetType(System.Double)) Then
            Return "DOUBLE"
        Else
            Return String.Empty
        End If
    End Function

however it sort of defeats the purpose of generics when you need the generic class to be aware of specific types... you might be better off with a non generic class that just has overloads for the 2 different types...