WithEvents variable giving Serialization Problems

[rbulph]

When I run the following code I get a message that the Parent class is not marked as serializable. This is very annoying since I'm not trying to serialize the Parent. Is this is a bug in Visual Studio? How do I get around it?

 

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

Public Class Form1

   Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

       Dim FileStream As Stream = File.Create("C:\abc.abc")

       Dim serializer As New BinaryFormatter
       With serializer
           
           Dim Child1 As New Child
           Dim Parent1 As Parent = New Parent(Child1)

           .Serialize(FileStream, Child1)  'Get an error at this line - "Parent... is not marked as Serializable."

       End With

   End Sub
End Class

Public Class Parent
   Inherits PictureBox 'this is why I can't serialise the Parent class
   Friend WithEvents MyChild As Child

   Friend Sub New(ByVal newChild As Child)
       MyChild = newChild
       newChild.MyParent = Me
   End Sub

   Private Sub ChildNotify() Handles MyChild.InformParent
       '
   End Sub
End Class

<Serializable()> Public Class Child

   Event InformParent()

   <NonSerialized()> Friend MyParent As Parent

End Class

[PlausiblyDamp]

It looks as though the automatic serialization support is attempting to serialize the target of the event (i.e. Parent) as this also happens if you don't declare it WithEvents but use the AddHandler statement instead.

 

If you implement the ISerializable interface however you have control over what does and doesn't get serialized - that should avoid this problem.

[rbulph]

Thanks. If I mark Parent as Serializable, implement ISerializable in Parent, adding:

 

   Public Sub GetObjectData(ByVal info As System.Runtime.Serialization.SerializationInfo, ByVal context As System.Runtime.Serialization.StreamingContext) Implements System.Runtime.Serialization.ISerializable.GetObjectData

   End Sub

   Friend Sub New(ByVal info As System.Runtime.Serialization.SerializationInfo, ByVal context As System.Runtime.Serialization.StreamingContext)
       InitializeComponent()

   End Sub

 

so that, although Parent is serializable, nothing gets serialized, the problem seems to be resolved.

[rbulph]

Problem is, the deserialization creates a ghost Parent to handle the events. Even if I put InitializeComponent in the new New Sub it doesn't seem to get created properly and there are errors when it's constituent controls get referenced. If I try to Serialize the Parent property of Child, and then substitute the deserialized Parent with a new Parent, the problem doesn't go away.

 

Maybe the best solution is to simply remove all the event handling while I'm saving and add it in as soon as I've finished.

[PlausiblyDamp]

If the child class implements the ISerializable interface then you would save / load the required bits but just don't save anything regarding the event.

[rbulph]

OK, after a break have gone back to this and got it to work, with some help from this article http://www.codeproject.com/KB/vb/serializevbclasses.aspx.

 

Outstanding problems are that it seems to take a lot of processor power to open files now and I have a static variable in one of my procedures that leads to an error sometimes on deserialization (field can't be found). I've now marked this as nonserializable so hopefully that will do the trick.

[rbulph]

The slowness seems to be the result of this (unrelated) code which is currently called during deserialization and which takes half a second to complete:

 

 Private Function PrintingArea() As Rectangle

       'Return the area of the paper that printing is to take place on.
       With PrintDocument1.DefaultPageSettings
           Return New Rectangle(.Margins.Left, .Margins.Top, .Bounds.Width - .Margins.Left - .Margins.Right, .Bounds.Height - .Margins.Top - .Margins.Bottom)
       End With

   End Function

 

Don't know why this should be so slow.

[PlausiblyDamp]

Without profiling the code it is a bit speculative but I would be interested in knowing what the PrintDocument1.DefaultPageSettings is doing behind the scenes. It might be querying some OS / printer information - that could be taking the time.

 

It is possibly worth checking when / why this is being called and seeing if that could be addressed.

[rbulph]

I suppose I could probably speed it up by just querying the Margins and Bounds once and storing them.