XML Serializable Dictionary in .NET

For some reason, the generic Dictionary in .NET 2.0 is not XML serializable. The following code snippet is a XML serializable generic dictionary. The dictionary is serializable by implementing the IXmlSerializable interface.

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Serialization;

[XmlRoot(“dictionary”)]
public class SerializableDictionary<TKey, TValue>
: Dictionary<TKey, TValue>, IXmlSerializable
{
#region IXmlSerializable Members
public System.Xml.Schema.XmlSchema GetSchema()
{
return null;
}

public void ReadXml(System.Xml.XmlReader reader)
{
XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));

bool wasEmpty = reader.IsEmptyElement;
reader.Read();

if (wasEmpty)
return;

while (reader.NodeType != System.Xml.XmlNodeType.EndElement)
{
reader.ReadStartElement(“item”);

reader.ReadStartElement(“key”);
TKey key = (TKey)keySerializer.Deserialize(reader);
reader.ReadEndElement();

reader.ReadStartElement(“value”);
TValue value = (TValue)valueSerializer.Deserialize(reader);
reader.ReadEndElement();

this.Add(key, value);

reader.ReadEndElement();
reader.MoveToContent();
}
reader.ReadEndElement();
}

public void WriteXml(System.Xml.XmlWriter writer)
{
XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));

foreach (TKey key in this.Keys)
{
writer.WriteStartElement(“item”);

writer.WriteStartElement(“key”);
keySerializer.Serialize(writer, key);
writer.WriteEndElement();

writer.WriteStartElement(“value”);
TValue value = this[key];
valueSerializer.Serialize(writer, value);
writer.WriteEndElement();

writer.WriteEndElement();
}
}
#endregion
}

Another convenient way around it is to use a .NET class called KeyedCollection. KeyedCollection derives from the iList interface instead of iDictionary, and is therefore serializable, but also allows you to specify a key. This class is an abstract type, so you must derive your own custom class, but as we’ll see in a second, that’s a snap.

KeyedCollection must be inherited because it has to be a list of a specific object type. Then, instead of specifying your own key value for each item in the list, you indicate which of the object’s fields you want to be used as the key.

Public Class SourceTypeList
Inherits System.Collections.ObjectModel.KeyedCollection(Of Long, SourceType)
Protected Overrides Function GetKeyForItem(ByVal item As SourceType) As Long
Return item.SourceTypeID
End Function
Sub New()
MyBase.New()
End Sub
End Class

What does this code do? It tells Visual Basic to create a new type collection derived from KeyedCollection, where the key is a long integer and the value is an object of type SourceType (SourceType represents information about a type of syndication file, such as Atom 0.3 or RSS 2.0). You then overried the function GetKeyForItem and tell VB which field you want to use as the key.

Reference:
www.myboogpages.com/2006/12/net-dictionary-serialization-problem.html