Serialization problem

[Alan Balkany]

I'm having a hard time deserializing old versions of a class after adding a new member. I've written a toy program that's the simplest possible example of this problem. Maybe someone else might notice what I'm doing wrong. I have a class with one member: A System.Drawing.Color:

\[Serializable\]
public class SerialObj
{
    public System.Drawing.Color color;
}

The following code serializes/deserializes it with no problem:

        SoapFormatter formatter = new SoapFormatter();     // Serialize:
        formatter.AssemblyFormat = System.Runtime.Serialization.Formatters.FormatterAssemblyStyle.Simple;
        formatter.Serialize(myStream, so);

        SoapFormatter formatter = new SoapFormatter();     // Deserialize:
        formatter.AssemblyFormat = System.Runtime.Serialization.Formatters.FormatterAssemblyStyle.Simple;
        so = (SerialObj)formatter.Deserialize(myStream);

I added an int member, and I'm trying to use the ISerializable interface to handle the different versions. This interface requires a constructor with two special parameters, and a GetObjectData method:

\[Serializable\]
public class SerialObj : ISerializable
{
    public System.Drawing.Color color;
    public int number;                   // The new member.

    public SerialObj()
    {
        System.Windows.Forms.MessageBox.Show("In empty ctor.");
    }


    public SerialObj(SerializationInfo info, StreamingContext cntxt)
    {
        System.Windows.Forms.MessageBox.Show("In full ctor.");
        color = (System.Drawing.Color)info.GetValue("color", typeof(System.Drawing.Color));

        try
        {
            number = info.GetInt32("number");
        }
        catch (Exception ex)
        {
            System.Windows.Forms.MessageBox.Show(ex.Message);
        }
    }


    void ISerializable.GetObjectData(SerializationInfo inf, StreamingContext cxt)
    {
        System.Windows.Forms.MessageBox.Show("In GetObjectData.");
        inf.AddValue("color", color);
        inf.AddValue("number", number);
    }
}

It works for serialized new versions with both members. But when I deserialize an old version (without the int), it crashes on the Deserialize call, with the exception: "Top Object cannot be instantiated for element 'color'." It never even calls either constructor. Can

[Migounette]

Try this.... // Version 1.0 [Serializable] public class SerialObj { public System.Drawing.Color color; } // Version 2.0 [Serializable] public class SerialObj { public System.Drawing.Color color; [OptionalField(VersionAdded = 2)] public int number; } // Version 3.0 [Serializable] public class SerialObj { public System.Drawing.Color color; [OptionalField(VersionAdded=2)] public int number; [OptionalField(VersionAdded=3)] public int solution; }

[Alan Balkany]

Thanks for the suggestion, but according to this (http://msdn.microsoft.com/en-us/library/ms229752.aspx[^]) the OptionalField attribute doesn't work with the SoapFormatter (just the BinaryFormatter). Versions have been released using the SoapFormatter, so I can't change it at this point.

[Luc Pattyn]

Hi Alan, I haven't studied the subject yet, however it so happens I just read a CP thread about this, and it seems you need to use SerializationBinder class. MSDN even holds an example. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

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[Alan Balkany]

Thanks Luc. I have tried using a custom SerializationBinder (for the formatter.Binder member). It implements a single method, BindToType, which appears to be used repeatedly as a subroutine for the .NET framework serialization, that returns a Type when given a typeName string. It didn't avoid the error message I'm getting. The error happens after the return from the Binder, with the type that had the added member.

[Alan Balkany]

Migounette, I tried your suggestion anyway, and it works with the new versions (both members), but not with the old versions (color member only). The error message is: "Member at position 0 was null. Parameter name: members". I don't have any variable named "members", so it must be referring to something internal to .NET.

[Migounette]

Not sure about the error Members of what ? Try this: public int number { get; set; } or I was looking at SOAP (never played with), but maybe with the extension of the attribute for soap envelop may work. http://msdn.microsoft.com/en-us/library/system.xml.serialization.soapignoreattribute.aspx[^] Good luck :)