[RESOLVED] [2005] Problem Serializing

[FourBlades]

Sure thing.

[FourBlades]

Solution To Problem:
The problem was as follows:
When you serialize an object (I'm using the BinaryFormatter) an object graph is created that includes any object pointed to by the primary object being serialized. If the primary object being serialized contains a delegate (as in maybe an event delegate) andalso another object has subscribed to receive an event notification from the primary object (the one being serialized) then the subscribing object is also included in the object graph. The runtime attempts to serialize the subscribing object. If the subscribing object is not serializable, an error occurs.

The solution to this problem is to exclude the delegates from being serialized.
To exclude the delegates from being serialized you must handle custom serialization.
Custom serialization requires the class author to implement the ISerializable interface.
Within the implementation of the ISerializable interface you must write code to exclude any class members of type Delegate or any type that derives from Delegate.

The complete Person class that implements the ISerializable interface is shown below:

Imports System
Imports System.Security.Permissions
Imports System.Runtime.Serialization

Namespace Utilities

    <Serializable()> _
    Public Class Person
        Implements ISerializable

#Region "Event And Delegate Declarations"

        '<Serializable()> _
        Public Delegate Sub LastNameChangedEventHandler(ByVal sender As Object, ByVal e As LastNameChangedEventArgs)
        Public Event LastNameChanged As LastNameChangedEventHandler

        '<Serializable()> _
        Public Delegate Sub FirstNameChangedEventHandler(ByVal sender As Object, ByVal e As FirstNameChangedEventArgs)
        Public Event FirstNameChanged As FirstNameChangedEventHandler

#End Region

#Region "Private and Public Fields Not Wrapped By Properties (NONE)"

        'None

#End Region

#Region "Constructors"

        Sub New()
            Me.New("Unknown", "Unknown")
        End Sub

        Sub New(ByVal firstName As String, ByVal lastName As String)

            If (String.IsNullOrEmpty(firstName)) Then
                Throw New ArgumentNullException("firstName")
            Else
                mFirstName = firstName
            End If

            If (String.IsNullOrEmpty(lastName)) Then
                Throw New ArgumentNullException("lastName")
            Else
                mLastName = lastName
            End If

        End Sub

        'The CLR calls this special constructor when this (Me) object is deserialized
        'Should have Protected scope if other classes can be inherited from this class
        'Otherwise, if this class is sealed (cannot be inherited from) the scope can be Private
        Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
            SerializationHelpers.ISerializableContructorHelper(info, context, Me)
        End Sub

        <SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
        Protected Overridable Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext) _
          Implements ISerializable.GetObjectData

            SerializationHelpers.GetObjectDataHelper(info, context, Me)

        End Sub

#End Region

#Region "Instance Public Properties and Their Wrapped Fields"

        Private mLastName As String
        Public Property LastName() As String
            Get
                Return mLastName
            End Get
            Set(ByVal value As String)
                If Not mLastName = value Then
                    Dim Args As New LastNameChangedEventArgs(mLastName, value, Me)
                    Me.OnLastNameChanged(Args)
                    mLastName = value
                End If
            End Set
        End Property

        Private mFirstName As String
        Public Property FirstName() As String
            Get
                Return mFirstName
            End Get
            Set(ByVal value As String)
                If Not mFirstName = value Then
                    Dim args As New FirstNameChangedEventArgs(mFirstName, value, Me)
                    Me.OnFirstNameChanged(args)
                    mFirstName = value
                End If
            End Set
        End Property

#End Region

#Region "Instance Public Methods"

        Public Overrides Function ToString() As String
            Return String.Concat(FirstName, " ", LastName)
        End Function

        Protected Overridable Sub OnLastNameChanged(ByVal e As LastNameChangedEventArgs)
            RaiseEvent LastNameChanged(Me, e)
        End Sub

        Protected Overridable Sub OnFirstNameChanged(ByVal e As FirstNameChangedEventArgs)
            RaiseEvent FirstNameChanged(Me, e)
        End Sub

#End Region

#Region "Static Public Methods and Properties (NONE)"

        'NONE

#End Region

#Region "Methods In Interfaces (NONE)"

        'NONE

#End Region

#Region "Private Helper Methods (NONE)"

        'NONE

#End Region

    End Class

End Namespace

[FourBlades]

Opps clicked on Submit Reply instead of Preview Post...more in next post

[FourBlades]

You'll notice a Protected Sub New and a Protected Overridable Sub GetObjectData highlighted in bold text within the Person class listed two posts above.
These are the two additional code blocks required by the ISerializable interface.

You'll also notice that in those blocks reference is made to a helper class as found below:

Credit for the code goes to the authors of Practical Guidelines And Best Practices For Microsoft Visual Basic and Visual C# Developers a book I would highly recommend to anyone.

Imports System.Runtime.Serialization
Imports System.Reflection

Namespace Utilities

    Public Class SerializationHelpers

        ''' <summary>
        ''' Helper routine for serializing objects.
        ''' (Place a call to this sub into the Serializable Classes Protected Overridable Sub GetObjectData)
        ''' i.e. place into: Protected Overridable Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext)
        ''' </summary>
        ''' <param name="info"></param>
        ''' <param name="context"></param>
        ''' <param name="obj"></param>
        ''' <remarks></remarks>
        Public Shared Sub GetObjectDataHelper(ByVal info As SerializationInfo, ByVal context As StreamingContext, ByVal obj As Object)

            'Get list of serializable members
            Dim members() As MemberInfo = GetFilteredSerializableMembers(obj.GetType)

            'Read the value of each member
            Dim values() As Object = FormatterServices.GetObjectData(obj, members)

            'Store in the SerializationInfo Object, using member name
            For i As Integer = 0 To members.Length - 1
                info.AddValue(members(i).Name, values(i))
            Next

        End Sub

        ''' <summary>
        ''' Helper routine for deserializing objects.
        ''' Place a call to this function into the Serializable Constructor; 
        ''' i.e. place into:   Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext))
        ''' </summary>
        ''' <param name="info"></param>
        ''' <param name="context"></param>
        ''' <param name="obj"></param>
        ''' <remarks></remarks>
        Public Shared Sub ISerializableContructorHelper(ByVal info As SerializationInfo, ByVal context As StreamingContext, ByVal obj As Object)

            'Get the list of serializable members for this object 
            'excluding members that are of type delegate (filtered)
            'Note that members()(below) contains all types of members from the class passed into this sub via obj (byval obj as Object)
            Dim members() As MemberInfo = GetFilteredSerializableMembers(obj.GetType)

            Dim values(members.Length - 1) As Object

            'Read the value for each member
            For i As Integer = 0 To members.Length - 1

                'retrieve the members from members() that are of type field
                'and then get all field's values
                Dim member As MemberInfo = members(i)
                If member.MemberType = MemberTypes.Field Then
                    Dim membertype As Type = CType(member, FieldInfo).FieldType
                    values(i) = info.GetValue(member.Name, membertype)
                End If
            Next

            'assign all serializable members in one operation
            FormatterServices.PopulateObjectMembers(obj, members, values)

        End Sub

        ''' <summary>
        ''' Return an array of serializable MemberInfo for a given type.
        ''' (Same as FormatterServices.GetSerializableMember, but FILTERS OUT delegate fields.)
        ''' </summary>
        ''' <param name="ty"></param>
        ''' <returns></returns>
        ''' <remarks></remarks>
        Private Shared Function GetFilteredSerializableMembers(ByVal ty As Type) As MemberInfo()

            Dim al As New ArrayList

            'Get the list of serializable members
            For Each mi As MemberInfo In FormatterServices.GetSerializableMembers(ty)

                'Add the mi object to the arraylist if it is NOT:
                '(a FieldInfo object) [that IS also (AndAlso)] (found in the inheritance hierarchy of the Delegate class)
                If Not (TypeOf mi Is FieldInfo AndAlso GetType([Delegate]).IsAssignableFrom(DirectCast(mi, FieldInfo).FieldType)) Then
                    al.Add(mi)
                End If
            Next
            Return DirectCast(al.ToArray(GetType(MemberInfo)), MemberInfo())
        End Function

    End Class

End Namespace

You'll have to read up on the ISerializable interface and the purpose of it's members because a complete explanation would be lengthy.
Upon reading up on how these two code blocks work in general; i.e. the purpose for the special sub New and the GetObjectData method you'll quickly see the importance of these helper methods.

A complete example including the using class, the simple Person class, and the Helper class follows In the next post (was not accepted to this post because of it's size):

[FourBlades]

Using Class example:

Imports System.Runtime.Serialization
Imports System.Runtime.Serialization.Formatters.Binary
Imports System.IO
Imports DILU.Utilities

Public Class Form1

#Region "Serialize"

    Private Sub Serialize(ByVal fileName As String, ByVal person As Person)

        Dim fs As FileStream = New FileStream(fileName, FileMode.OpenOrCreate)

        Dim bf As New BinaryFormatter
        Try
            bf.Serialize(fs, person)
        Catch exception As SerializationException
            MessageBox.Show("Failed to serialize. Reason: " & exception.Message)
            Throw
        Finally
            fs.Close()
        End Try

    End Sub

#End Region

#Region "Deserialize"

    Private Function Deserialize(ByVal fileName As String) As Person

        Dim fs As FileStream = New FileStream(fileName, FileMode.Open)

        Dim p As New Person
        Try

            Dim formatter As New BinaryFormatter
            p = DirectCast(formatter.Deserialize(fs), Person)

        Catch exception As Runtime.Serialization.SerializationException
            Console.WriteLine("Failed to deserialize. Reason: " & exception.Message)
            Throw
        Finally
            fs.Close()
        End Try

        Return p

    End Function

#End Region

#Region "Button One Click"

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim p As Person
        Try
            p = New Person(" ", " ")
        Catch ex As ArgumentNullException
            p = Nothing
            p = New Person
        End Try

        Me.TextBox1.Text = p.FirstName
        Me.TextBox2.Text = p.LastName

        'yes, I actually do have a need for these two events :)
        AddHandler p.LastNameChanged, AddressOf PersonsLastNameChanged
        AddHandler p.FirstNameChanged, AddressOf PersonsFirstNameChanged

        Serialize("C:\BinaryNoDelegateSerialization.txt", p)
        Dim np As Person = Deserialize("C:\BinaryNoDelegateSerialization.txt")

        Me.TextBox3.Text = np.FirstName
        Me.TextBox4.Text = np.LastName

        Application.DoEvents()

        Threading.Thread.Sleep(3000)

        p.LastName = "New Last Name"
        p.FirstName = "New First Name"

    End Sub

#End Region

#Region "Event Handlers For Names Changed"

    Private Sub PersonsLastNameChanged(ByVal sender As Object, ByVal e As LastNameChangedEventArgs)
        Me.TextBox2.Text = e.NewLastName
    End Sub

    Private Sub PersonsFirstNameChanged(ByVal sender As Object, ByVal e As FirstNameChangedEventArgs)
        Me.TextBox1.Text = e.NewFirstName
    End Sub

#End Region

End Class

Person Class:

Imports System
Imports System.Security.Permissions
Imports System.Runtime.Serialization

Namespace Utilities

    <Serializable()> _
    Public Class Person
        Implements ISerializable

#Region "Event And Delegate Declarations"

        '<Serializable()> _
        Public Delegate Sub LastNameChangedEventHandler(ByVal sender As Object, ByVal e As LastNameChangedEventArgs)
        Public Event LastNameChanged As LastNameChangedEventHandler

        '<Serializable()> _
        Public Delegate Sub FirstNameChangedEventHandler(ByVal sender As Object, ByVal e As FirstNameChangedEventArgs)
        Public Event FirstNameChanged As FirstNameChangedEventHandler

#End Region

#Region "Private and Public Fields Not Wrapped By Properties (NONE)"

        'None

#End Region

#Region "Constructors"

        Sub New()
            Me.New("Unknown", "Unknown")
        End Sub

        Sub New(ByVal firstName As String, ByVal lastName As String)

            If (String.IsNullOrEmpty(firstName)) Then
                Throw New ArgumentNullException("firstName")
            Else
                mFirstName = firstName
            End If

            If (String.IsNullOrEmpty(lastName)) Then
                Throw New ArgumentNullException("lastName")
            Else
                mLastName = lastName
            End If

        End Sub

        'The CLR calls this special constructor when this (Me) object is deserialized
        'Should have Protected scope if other classes can be inherited from this class
        'Otherwise, if this class is sealed (cannot be inherited from) the scope can be Private
        Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
            SerializationHelpers.ISerializableContructorHelper(info, context, Me)
        End Sub

        <SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
        Protected Overridable Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext) _
          Implements ISerializable.GetObjectData

            SerializationHelpers.GetObjectDataHelper(info, context, Me)

        End Sub

#End Region

#Region "Instance Public Properties and Their Wrapped Fields"

        Private mLastName As String
        Public Property LastName() As String
            Get
                Return mLastName
            End Get
            Set(ByVal value As String)
                If Not mLastName = value Then
                    Dim Args As New LastNameChangedEventArgs(mLastName, value, Me)
                    Me.OnLastNameChanged(Args)
                    mLastName = value
                End If
            End Set
        End Property

        Private mFirstName As String
        Public Property FirstName() As String
            Get
                Return mFirstName
            End Get
            Set(ByVal value As String)
                If Not mFirstName = value Then
                    Dim args As New FirstNameChangedEventArgs(mFirstName, value, Me)
                    Me.OnFirstNameChanged(args)
                    mFirstName = value
                End If
            End Set
        End Property

#End Region

#Region "Instance Public Methods"

        Public Overrides Function ToString() As String
            Return String.Concat(FirstName, " ", LastName)
        End Function

        Protected Overridable Sub OnLastNameChanged(ByVal e As LastNameChangedEventArgs)
            RaiseEvent LastNameChanged(Me, e)
        End Sub

        Protected Overridable Sub OnFirstNameChanged(ByVal e As FirstNameChangedEventArgs)
            RaiseEvent FirstNameChanged(Me, e)
        End Sub

#End Region

#Region "Static Public Methods and Properties (NONE)"

        'NONE

#End Region

#Region "Methods In Interfaces (NONE)"

        'NONE

#End Region

#Region "Private Helper Methods (NONE)"

        'NONE

#End Region

    End Class

End Namespace

First Name Changed Event Args Class:

Namespace Utilities

    <Serializable()> _
    Public Class FirstNameChangedEventArgs
        Inherits EventArgs

        Sub New(ByVal oldFirstName As String, ByVal newFirstName As String, ByVal sendingPerson As Person)
            mOldFirstName = oldFirstName
            mNewFirstName = newFirstName
        End Sub

        Private mOldFirstName As String
        Public ReadOnly Property OldFirstName() As String
            Get
                Return mOldFirstName
            End Get
        End Property

        Private mNewFirstName As String
        Public ReadOnly Property NewFirstName() As String
            Get
                Return mNewFirstName
            End Get
        End Property

        Private mPerson As Person
        Public ReadOnly Property Person() As Person
            Get
                Return mPerson
            End Get
        End Property

    End Class

End Namespace

The last name changed event args class is similar to the above code

The Serialization Helpers Class is posted again in the next post because it was not accepted here due to it's size.

[FourBlades]

The Serialization Helpers Class:

Imports System.Runtime.Serialization
Imports System.Reflection

Namespace Utilities

    Public Class SerializationHelpers

        ''' <summary>
        ''' Helper routine for serializing objects.
        ''' (Place a call to this sub into the Serializable Classes Protected Overridable Sub GetObjectData)
        ''' i.e. place into: Protected Overridable Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext)
        ''' </summary>
        ''' <param name="info"></param>
        ''' <param name="context"></param>
        ''' <param name="obj"></param>
        ''' <remarks></remarks>
        Public Shared Sub GetObjectDataHelper(ByVal info As SerializationInfo, ByVal context As StreamingContext, ByVal obj As Object)

            'Get list of serializable members
            Dim members() As MemberInfo = GetFilteredSerializableMembers(obj.GetType)

            'Read the value of each member
            Dim values() As Object = FormatterServices.GetObjectData(obj, members)

            'Store in the SerializationInfo Object, using member name
            For i As Integer = 0 To members.Length - 1
                info.AddValue(members(i).Name, values(i))
            Next

        End Sub

        ''' <summary>
        ''' Helper routine for deserializing objects.
        ''' Place a call to this function into the Serializable Constructor; 
        ''' i.e. place into:   Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext))
        ''' </summary>
        ''' <param name="info"></param>
        ''' <param name="context"></param>
        ''' <param name="obj"></param>
        ''' <remarks></remarks>
        Public Shared Sub ISerializableContructorHelper(ByVal info As SerializationInfo, ByVal context As StreamingContext, ByVal obj As Object)

            'Get the list of serializable members for this object 
            'excluding members that are of type delegate (filtered)
            'Note that members()(below) contains all types of members from the class passed into this sub via obj (byval obj as Object)
            Dim members() As MemberInfo = GetFilteredSerializableMembers(obj.GetType)

            Dim values(members.Length - 1) As Object

            'Read the value for each member
            For i As Integer = 0 To members.Length - 1

                'retrieve the members from members() that are of type field
                'and then get all field's values
                Dim member As MemberInfo = members(i)
                If member.MemberType = MemberTypes.Field Then
                    Dim membertype As Type = CType(member, FieldInfo).FieldType
                    values(i) = info.GetValue(member.Name, membertype)
                End If
            Next

            'assign all serializable members in one operation
            FormatterServices.PopulateObjectMembers(obj, members, values)

        End Sub

        ''' <summary>
        ''' Return an array of serializable MemberInfo for a given type.
        ''' (Same as FormatterServices.GetSerializableMember, but FILTERS OUT delegate fields.)
        ''' </summary>
        ''' <param name="ty"></param>
        ''' <returns></returns>
        ''' <remarks></remarks>
        Private Shared Function GetFilteredSerializableMembers(ByVal ty As Type) As MemberInfo()

            Dim al As New ArrayList

            'Get the list of serializable members
            For Each mi As MemberInfo In FormatterServices.GetSerializableMembers(ty)

                'Add the mi object to the arraylist if it is NOT:
                '(a FieldInfo object) [that IS also (AndAlso)] (found in the inheritance hierarchy of the Delegate class)
                If Not (TypeOf mi Is FieldInfo AndAlso GetType([Delegate]).IsAssignableFrom(DirectCast(mi, FieldInfo).FieldType)) Then
                    al.Add(mi)
                End If
            Next
            Return DirectCast(al.ToArray(GetType(MemberInfo)), MemberInfo())
        End Function

    End Class

End Namespace

[FourBlades]

Due to the low number of replys to my original question in this thread, I assume that either the explanation was too lengthy or that not many people use custom serialization.

Therefore, I decided to post a complete example others may find useful in the future.

If anyone finds any errors in this code please let me know and I'll make corrections here for future viewers to see.

Thanks