When using ISerializable with DataContractSerializer, how do I stop the serializer from outputting type information?

Question

To get more control over serialization, I have converted a class from [DataContract] to [Serializable], implementing both GetObjectData and the special deserializing constructor. When I do this, the XML emitted now has type information applied to all elements. I don't want this superfluous information, and I'm wondering how to inform the serializer to not output it.

Here's the sample code that uses [DataContract]:

[DataContract(Namespace = "")]
class Test 
{
    public Test() { }
    [DataMember]
    public Nullable<int> NullableNumber = 7;
    [DataMember]
    public int Number = 5;

    public static void Go()
    {
        var test = new Test();
        var dcs = new DataContractSerializer(typeof(Test));
        using (var s = new StreamWriter("test.xml"))
        {
            dcs.WriteObject(s.BaseStream, test);
        }
    }        
}

This outputs the following XML (notice no type info on Nullable Number and Number--this is the desired output):

<Test xmlns:i="http://www.w3.org/2001/XMLSchema-instance"&gt;
  <NullableNumber>7</NullableNumber>
  <Number>5</Number>
</Test>

If I modify the above code as follows (adding [Serializable], : ISerializable, and the two serialization methods):

[Serializable]
class Test : ISerializable
{
    public Test() { }
    public Nullable<int> NullableNumber = 7;
    public int Number = 5;

    public static void Go()
    {
        var test = new Test();
        var dcs = new DataContractSerializer(typeof(Test));
        using (var s = new StreamWriter("test.xml"))
        {
            dcs.WriteObject(s.BaseStream, test);
        }
    }        
    public Test(SerializationInfo info, StreamingContext context)
    {
        NullableNumber = info.GetInt32("NullableNumber");
        Number = info.GetInt32("Number");
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("NullableNumber", NullableNumber);
        info.AddValue("Number", Number);
    }
}

It now emits the following XML. Notice the type information (i:type="x:int") added to each element.

<Test xmlns="http://schemas.datacontract.org/2004/07/XMLSerialization" xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns:x="http://www.w3.org/2001/XMLSchema"&gt;
  <NullableNumber i:type="x:int" xmlns="">7</NullableNumber>
  <Number i:type="x:int" xmlns="">5</Number>
</Test>

Why is it doing this? How do I stop it from doing it?

Thanks!

Answer 1

Do you need the ISerializable here? What was the regular DataContractSerializer not giving you? If you switch back to this, it should work fine.

Basically, by implementing custom serialization, the data is no longer contract based - so it has to include this extra information to guarantee that it is able to understand it later.

So: is there a reason to implement ISerializable in this case?

Answer 2

Due to this and many other reasons, I cannot use the DataContractSerializer. Instead, I chose to role my own serialization.