XML Serialize dynamic object

Question

I need to construct a set of dynamically created XML nodes from objects on the following format:

<Root>
    <Name>My Name</Name>
    <DynamicValues>
        <DynamicValue1>Value 1</DynamicValue1>
        <DynamicValue2>Value 2</DynamicValue2>
    </DynamicValues>
</Root>

The name of the nodes within the DynamicValues-tag are not known in advance. My initial thought was that this should be possible using an Expando Object, e.g:

[DataContract]
public class Root
{
    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public dynamic DynamicValues { get; set; }
}

by initializing it with the values:

var root = new Root
                    {
                        Name = "My Name",
                        DynamicValues = new ExpandoObject()
                    };

root.DynamicValues.DynamicValue1 = "Value 1";
root.DynamicValues.DynamicValue2 = "Value 2";

and then Xml-serialize it:

string xmlString;

var serializer = new DataContractSerializer(root.GetType());
using (var backing = new StringWriter())
using (var writer = new XmlTextWriter(backing))
{
    serializer.WriteObject(writer, root);
    xmlString = backing.ToString();
}

However, when I run this, I get an SerializationException saying:

"Type 'System.Dynamic.ExpandoObject' with data contract name 'ArrayOfKeyValueOfstringanyType:http://schemas.microsoft.com/2003/10/Serialization/Arrays' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer."

Any ideas how I can achieve this?

Solution

[Serializable]
public class DynamicSerializable : DynamicObject, ISerializable
{
    private readonly Dictionary<string, object> dictionary = new Dictionary<string, object>();

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        dictionary[binder.Name] = value;

        return true;
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        foreach (var kvp in dictionary)
        {
            info.AddValue(kvp.Key, kvp.Value);
        }
    }
}

[KnownType(typeof(DynamicSerializable))]
[DataContract]
public class Root
{
    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public dynamic DynamicValues { get; set; }
}

Output:

<Program.Root xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://
schemas.datacontract.org/2004/07/">
  <DynamicValues i:type="Program.DynamicSerializable">
    <DynamicValue1 xmlns:d3p1="http://www.w3.org/2001/XMLSchema" i:type="d3p1:st
ring" xmlns="">Value 1</DynamicValue1>
    <DynamicValue2 xmlns:d3p1="http://www.w3.org/2001/XMLSchema" i:type="d3p1:st
ring" xmlns="">Value 2</DynamicValue2>
  </DynamicValues>
  <Name>My Name</Name>
</Program.Root>

Comments

[Olav Haugen]

It does indeed serialize without throwing exceptions, but not into what I expected (see example XML in question). I get nodes of the type KeyValueOfstringanyType.