Deserialization constructor not called

Question

I am attempting to serialize/deserialize an object that contains a Dictionary<Tuid,Section>. These are both custom types.

In my code I have a type of Template which contains the Dictionary<Tuid,Section>. It is the Template class that I am attempting to serialize/deserialze.

To resolve the problem that this collection is a Dictionary I have implemented the ISerializable interface on my Template class....

[Serializable]
public class Template : ISerializable
{
    protected Template(SerializationInfo info, StreamingContext context)
    {
        // Deserialize the sections
        List<Tuid> tuids = (List<Tuid>)info.GetValue("Sections_Keys", typeof(List<Tuid>));
        List<Section> sections = (List<Section>)info.GetValue("Sections_Values", typeof(List<Section>));
        this._sections = new Dictionary<Tuid, Section>();

        for (int i = 0; i < tuids.Count; i++)
        {
            _sections.Add(tuids[i], sections[i]);
        }           
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        List<Tuid> tuids = new List<Tuid>();
        List<Section> sections = new List<Section>();

        foreach (KeyValuePair<Tuid, Section> kvp in _sections)
        {
            tuids.Add(kvp.Key);
            sections.Add(kvp.Value);
        }

        info.AddValue("Sections_Keys", tuids, typeof(List<Tuid>));
        info.AddValue("Sections_Values", sections, typeof(List<Section>));
   }

The strategy here is to "unpack" the dictionary into two seperate lists and store them individually in the serialized stream. Then they are re-created afterwards.

My Section class also implments ISerializable...

[Serializable]
public class Section : BaseObject
{

    protected Section(SerializationInfo info, StreamingContext context):base(.....)
    {
        // Code
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
       // code
    }
}

The problem is that when I serialize GetObjectData() is called on both my Template and my Section which makes me believe that the data is Serializable and that its getting serialized.

When I deserialize, only the deserialize constructor on Template is called. The deserialize constructor for Section is never called. The result of this is that the call to info.GetValue("Section_Values"....) does return a List but it has one item in it and that item is null.

Why does my constructor to deserialize a Section never get called? Could it be that some of the data inside the section is not serializable? If so, how to find out what exactly it cannot serialize?

Update: One thing I have just spotted is that the BaseObject for section is marked with [Serializable] but does not implement ISerializable.

Additionally, Im wondering how fussy the Deserialize code is - will it target a constructor that also constructs a base class?

Update..

Ok, Ive tracked down the problem to the Serialization of the Section. The code looks something like this...

protected Section(SerializationInfo info, StreamingContext context):base(.....)
{
    // Code
}

public void GetObjectData(SerializationInfo info, StreamingContext context)
{

    //info.AddValue("CustomObject", ClientInfo, typeof(CustomObject));
    //info.AddValue("Description", Description, typeof(string));
}

With both of the lines commented out, nothing is serialized and the deserialization constructor is called on Section. If I add in the string value everything is still fine. However, yes - you guessed it - if I add the CustomObject into the serialization stream then the deserialization constructor is not called.

Note that...

• My deserialization constructor for Section is a blank method - I dont attempt to do anything with the deserialized data.
• The base constructor for Section has been stubbed out to pass in new valid objects and I have confirmed that this runs fine.
• No exceptions are thrown to tell me that the CustomObject cannot be serialized.
• The CustomObject is serializable and its GetObjectData() method runs fine and its constructed fine on deserialization.

It seems strange that purely be adding this serializable object to the stream that the framework then just fails to the deserializer constructor of Section!!

Why could this possibly be happening?

Anethole

I like your approach to serializing Dictionary:) – Idiocrasy

I have no idea if its a good approach :) well it doesnt work at the moment so can't be that good :) – Anethole

How have you managed to get the GetObjectData to be called ? I am trying this for some time and this method just never gets called – Baxley

Answer 1

One of the options is to implement

[OnDeserializing]
void OnDeserializing(StreamingContext c)
{
    //create what is required here
}

in theTemplate class, as the default serrializer does not call the constructor for child objects - Section class

Laminitis

Ok, looks like a good idea - how to extract my child objects into my Template class? Additionally, its strange how the deserialization knows that there is 1 object in the list but that its null. – Anethole

I am not too sure, but I would assume you could reuse your code from the constructors of Template and Section – Laminitis

I think that this is more intended to set values up in the class that you dont want to serialize. E.g. if you had a calculated value that you can work out from two other values. You could calculate it in this method. – Anethole

Answer 2

I believe your problem is because of the way serialization works (I seem to recall it's width first, rather than depth first). What this means is that it de-serializes your template and then creates space within there to add in your sections.

These sections however haven't yet been de-serialized, they'll be deserialized after the Template has finished de-serializing. You should be able to check this by using a break point and letting your code run on a bit further. The way to fix this is either oleksii's solution or similar to use IDeserializationCallback.

What IDeserializationCallback is when the instance has finished de-serializing (and it's members) it'll call into a method to allow you to do some wiring. I'd try something more like this below:

[Serializable]
public class Template : ISerializable, IDeserializationCallback
{
    private List<Tuid> tuids;
    private List<Section> sections
    protected Template(SerializationInfo info, StreamingContext context)
    {
        tuids = (List<Tuid>)info.GetValue("Sections_Keys", typeof(List<Tuid>));
        sections = (List<Section>)info.GetValue("Sections_Values", typeof(List<Section>));
        this._sections = new Dictionary<Tuid, Section>();
    }

    public void OnDeserialization(object sender)
    {
        // Section serialization constructor should have been called by this point
        for (int i = 0; i < tuids.Count; i++)
        {
            _sections.Add(tuids[i], sections[i]);
        } 
    }
}

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