This may be a simple question, but I'm struggling to find the answer
to it, so any suggestions would be greatly appreciated.... I want to
know if there's some way to ensure that the xsi:type attribute is
included when serializing a c# class.

The basic situation is this:
I have a class, ClassB which derives from ClassA.
ClassC contains a  list of ClassB, which I want to serialize as an
XmlArray of 'bListItem's as per the code below:

    [Serializable]
    [XmlType("classA")]
    public class ClassA
    {
        private string _id;

        [XmlAttribute("id")]
        public string Id
        {
            get { return _id; }
            set { _id = value; }
        }
    }

    [Serializable]
    [XmlType("classA.classB")]
    public class ClassB : ClassA
    {
        private string _name;

        [XmlAttribute("name")]
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    [Serializable]
    [XmlType("classC")]
    public class ClassC
    {
        private string _id;
        private List<ClassB> _bList;


        [XmlAttribute("id")]
        public string Id
        {
            get { return _id; }
            set { _id = value; }
        }

        [XmlArray("bList"), XmlArrayItem("bListItem")]
        public List<ClassB> BList
        {
            get { return _bList; }
            set { _bList = value; }
        }

    }


Now... this serializes to the following XML:

<?xml version="1.0" encoding="utf-8" ?>
<classC xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" id="C1">
    <bList>
         <bListItem id="B1" name="My B Item" />
    </bList>
</classC>

What I want to do is have the xsi:type of bListItem come through in
this element like so:

<?xml version="1.0" encoding="utf-8" ?>
<classC xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" id="C1">
    <bList>
         <bListItem xsi:type="classA.classB" id="B1" name="My B Item" /
>
    </bList>
</classC>


Can anyone tell me how to do this?

Thanks in advance...

Bonnie