Why doesn't XmlSerializer support Dictionary?

Question

Just curious as to why Dictionary is not supported by XmlSerializer ?

You can get around it easily enough by using DataContractSerializer and writing the object to a XmlTextWriter , but what are the characteristics of a Dictionary that makes it difficult for a XmlSerializer to deal with considering it's really an array of KeyValuePairs.

In fact, you can pass an IDictionary<TKey, TItem> to a method expecting an IEnumerable<KeyValuePairs<TKey, ITem>> .

Answer 1

Hashtables need hashcode and equality comparer providers generally. These cant be serialized easily in XML, and definitely will not be portable.

But I think you already found your answer. Just serialize the hashtable as a List<KeyValuePair<K,V>> and then (re)construct it into a hashtable.

Answer 2

This is waaay late - but I found this question whilst looking for the answer myself, and thought I'd share my eventual answer which was to replace XmlSerializer with a different tool that will serialize everything:

http://www.sharpserializer.com

It worked for me straight out of the box, serializing Dictionaries, and multi-layered custom types, and even generics using interfaces as type arguments. Also has a fully permissive license.

Thank you Pawel Idzikowski!

Answer 3

You can use ExtendedXmlSerializer . If you have a class:

public class TestClass
{
    public Dictionary<int, string> Dictionary { get; set; }
}

and create instance of this class:

var obj = new TestClass
{
    Dictionary = new Dictionary<int, string>
    {
        {1, "First"},
        {2, "Second"},
        {3, "Other"},
    }
};

You can serialize this object using ExtendedXmlSerializer:

var serializer = new ConfigurationContainer()
    .UseOptimizedNamespaces() //If you want to have all namespaces in root element
    .Create();

var xml = serializer.Serialize(
    new XmlWriterSettings { Indent = true }, //If you want to formated xml
    obj);

Output xml will look like:

<?xml version="1.0" encoding="utf-8"?>
<TestClass xmlns:sys="https://extendedxmlserializer.github.io/system" xmlns:exs="https://extendedxmlserializer.github.io/v2" xmlns="clr-namespace:ExtendedXmlSerializer.Samples;assembly=ExtendedXmlSerializer.Samples">
  <Dictionary>
    <sys:Item>
      <Key>1</Key>
      <Value>First</Value>
    </sys:Item>
    <sys:Item>
      <Key>2</Key>
      <Value>Second</Value>
    </sys:Item>
    <sys:Item>
      <Key>3</Key>
      <Value>Other</Value>
    </sys:Item>
  </Dictionary>
</TestClass>

You can install ExtendedXmlSerializer from nuget or run the following command:

Install-Package ExtendedXmlSerializer