Serialize custom collections of CollectionBase

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Introduction

This is a simple demo on how to serialize and deserialize custom collections, while handling derived collection items. This version also demos, serialize, deserialize of unknown derived types of cItem (see Eitem class).

Background

I wanted to be able to serialize using collections rather than arrays, allowing better type checking.

Using the code

This page does not display all the code, but the basic structure. Download the application for a demo on usage of the objects.

'-----------------------------------------

'The abstract item

'

'NOTE: Notice the attributes on the Citem, these are all the 

'derived types we plan to use in the collection

'

Option Explicit On 
Option Strict On

Imports System.Xml.Serialization

'NOTE: If you derrive from this clas, then add a

'XmlInclude attribute for the new class!


< _
XmlInclude(GetType(Yitem)), _
XmlInclude(GetType(XItem)), _
Serializable() _
> _
Public Class Citem
  Private m_Id As Integer
  Private m_Data As String

  Public Property Id() As Integer
     Get
        Return m_Id
     End Get
     Set(ByVal value As Integer)
        m_Id = value
     End Set
  End Property

  Public Property Data() As String
     Get
        Return m_Data
     End Get
     Set(ByVal value As String)
        m_Data = value
     End Set
  End Property

End Class


'-------------------------------------------

'derrived collection item

'This one has an extra property for the demon

'to show differences in XML output

'

Option Explicit On 
Option Strict On

Public Class XItem
    Inherits cItem

    Private m_D As Double

    Public Property D() As Double
        Get
            Return m_D
        End Get
     Set(ByVal value As Double)
        m_D = Value
     End Set
  End Property
End Class


'-----------------------------------------------

'derrived collection item

'

Option Explicit On 
Option Strict On

Public Class Yitem
    Inherits cItem

End Class


'--------------------------------------------

'derrived collection item


'NOTE: XmlInclude attribute is not included on cItem,

'This was done to demo Serialize/Deserialize 

'unknown derrived types of cItem


Option Explicit On 
Option Strict On

Public Class Eitem
  Inherits Citem

  Private m_B As Double

  Public Property B() As Double
     Get
        Return m_B
     End Get
     Set(ByVal value As Double)
        m_B = value
     End Set
  End Property

End Class


'---------------------------------------------------

'The Collection

'

Option Explicit On 
Option Strict On

Imports System.Xml
Imports System.IO

<Serializable()> _
Public Class MyCollection
  Inherits System.Collections.CollectionBase

  Public Overridable Function Add(ByVal value As cItem) As Integer
     MyBase.List.Add(value)
  End Function

  Default Public Overridable Property Item(ByVal index As Integer) As cItem
     Get
        Return DirectCast(MyBase.List.Item(index), cItem)
     End Get
     Set(ByVal value As cItem)
        MyBase.List.Item(index) = value
     End Set
  End Property

  Public Shared Sub SerializeObject(ByVal filename As String, _
   ByVal col As MyCollection, ByVal ExtraTypes() As System.Type)
     Try

        ' Create a new XmlSerializer instance.

        Dim s As New Xml.Serialization.XmlSerializer(_
         GetType(MyCollection), ExtraTypes)

        ' Writing the XML file to disk requires a TextWriter.

        Dim writer As New StreamWriter(filename)

        ' Serialize the object, and close the StreamWriter.

        s.Serialize(writer, col)
        writer.Close()

     Catch x As System.InvalidOperationException
        Throw New Exception("Check class cItem, all derrived "+ _
   "classes must be listed with the [ "+
   "XmlInclude(GetType(derrivedClass)) ] attribute!")
     End Try
  End Sub

  Public Shared Sub SerializeObject(ByVal filename As String, _
    ByVal col As MyCollection)
     Try
        ' Create a new XmlSerializer instance.

        Dim s As New Xml.Serialization.XmlSerializer(GetType(MyCollection))

        ' Writing the XML file to disk requires a TextWriter.

        Dim writer As New StreamWriter(filename)

        ' Serialize the object, and close the StreamWriter.

        s.Serialize(writer, col)
        writer.Close()

     Catch x As System.InvalidOperationException
        Throw New Exception("Check class cItem, all derrived classes "+ _
        "must be listed with the [ XmlInclude"+ _
        "(GetType(derrivedClass)) ] attribute!")
     End Try
  End Sub

  Public Shared Function DeserializeObject(ByVal filename As String, _
     ByVal ExtraTypes() As System.Type) As MyCollection
     Try
        Dim fs As New IO.FileStream(filename, FileMode.Open)
        Dim w As New Xml.Serialization.XmlSerializer( _
   GetType(MyCollection), ExtraTypes)
        Dim g As MyCollection = CType(w.Deserialize(fs), MyCollection)

        fs.Close()

        Return g

     Catch x As Exception
        Throw x
     End Try
  End Function

  Public Shared Function DeserializeObject(ByVal filename As String _
    ) As MyCollection
     Try
        Dim fs As New IO.FileStream(filename, FileMode.Open)
        Dim w As New Xml.Serialization.XmlSerializer(GetType(MyCollection))
        Dim g As MyCollection = CType(w.Deserialize(fs), MyCollection)

        fs.Close()

        Return g

     Catch x As Exception
        Throw x
     End Try
  End Function

End Class

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Subject   Author  Date  Specifying derived types at runtime solublefish 11:32 31 Dec '04   It turns out there's a way you can specify the derived types in your collection at runtime, rather than having to add an XMLInclude attribute for each one at design time. You can use reflection to find the types you're looking for and add an attribute for each to an XmlAttributes collection: XmlAttributes attrs = new XmlAttributes(); Assembly[] asms = AppDomain.CurrentDomain.GetAssemblies(); foreach(Assembly a in asms) { foreach(Module m in a.GetModules()) { foreach (Type t in m.GetTypes()) { if (t.IsSubclassOf(typeof(CItem))) { XmlElementAttribute xea = new XmlElementAttribute(); xea.ElementName = t.Name; xea.Type = t; attrs.XmlElements.Add(xea); } } } } Using the XmlAttributeOverrides classes, you can specify the attributes (created above) when creating the XMLSerializer, as described here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconoverridingserializationofclasseswithxmlattributeoverridesclass.asp[^] Sign In·View Thread·PermaLink Re: Specifying derived types at runtime eschneider100 17:52 31 Dec '04   That could be handy, But It's easier most of the time to just pass in the the extra types. See the overload with "ExtraTypes() as System.Type". I show an example in the downloaded code. Thia is the reason I updated the article. Anyway, That concept could be handy for other things. Thanks, Schneider Schneider Sign In·View Thread·PermaLink Serialization for ViewState drazz75 12:44 22 May '04   Eric: Your technique looks great. I was wondering if you had any information about how to save the serialization into viewstate rather than on disk? - Craig Sign In·View Thread·PermaLink 4.00/5 (1 vote) Re: Serialization for ViewState eschneider100 16:18 24 May '04   Well, I had to look-up viewstate.. Sounds like you need to implement IStateManager? Schneider Schneider Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: Serialization for ViewState lumonis 19:53 9 Dec '05   If you are looking to save it into memory for something like network transfer it's usually pretty simple to replace the FileStream with a MemoryStream and convert that to bytes. Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: Serialization for Web Service Renz81 2:52 10 Jan '07   Hi, I've been struggling with this for a couple of weeks now, I'm trying to Serialize a simple custom collection over a web service. I have a class that exposes among other things a custom collection. When consuming this class on the client side (a win app with a ref to the web service), the data is present but the collection seems to be missing the basic methods such as Add, Item & Count etc.. I take it this is what this article is trying to explain. My question is has anybody been able to do this via a web service or am I barking up the wrong tree? my custom collection inherits from collection base and does nothing special. Thanks for any help & advice. Sign In·View Thread·PermaLink Re: Serialization for Web Service eschneider100 13:17 24 Oct '07   Sorry its so late. This was not intended for web services, but. Basically the web service user has no idea what you objects are so you will get an array of you item objects. If you client has a reference to you Collection then just create an instance and call the AddRange method on the collection. Schneider Sign In·View Thread·PermaLink

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