How to serialize/deserialize to `Dictionary<int, string>` from custom XML not using XElement?

Question

Having empty Dictionary<int, string> how to fill it with keys and values from XML like

<items> <item id='int_goes_here' value='string_goes_here'/> </items> 

and serialize it back into XML not using XElement?

Answer 1

With the help of a temporary item class

public class item {     [XmlAttribute]     public int id;     [XmlAttribute]     public string value; } 

Sample Dictionary:

Dictionary<int, string> dict = new Dictionary<int, string>() {     {1,"one"}, {2,"two"} }; 

.

XmlSerializer serializer = new XmlSerializer(typeof(item[]),                                   new XmlRootAttribute() { ElementName = "items" }); 

Serialization

serializer.Serialize(stream,                dict.Select(kv=>new item(){id = kv.Key,value=kv.Value}).ToArray() ); 

Deserialization

var orgDict = ((item[])serializer.Deserialize(stream))                .ToDictionary(i => i.id, i => i.value); 

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Here is how it can be done using XElement, if you change your mind.

Serialization

XElement xElem = new XElement(                     "items",                     dict.Select(x => new XElement("item",new XAttribute("id", x.Key),new XAttribute("value", x.Value)))                  ); var xml = xElem.ToString(); //xElem.Save(...); 

Deserialization

XElement xElem2 = XElement.Parse(xml); //XElement.Load(...) var newDict = xElem2.Descendants("item")                     .ToDictionary(x => (int)x.Attribute("id"), x => (string)x.Attribute("value")); 

Answer 2

Paul Welter's ASP.NET blog has a dictionary that is serializeable. But it does not use attributes. I will explain why below the code.

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 } 

First, there is one gotcha with this code. Say you read a dictionary from another source that has this:

<dictionary>   <item>     <key>       <string>key1</string>     </key>     <value>       <string>value1</string>     </value>   </item>   <item>     <key>       <string>key1</string>     </key>     <value>       <string>value2</string>     </value>   </item> </dictionary> 

This will throw a exception on de-seariazation because you can only have one key for a dictionary.

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The reason you MUST use a XElement in a seriazed dictionary is dictionary is not defined as Dictionary<String,String>, a dictionary is Dictionary<TKey,TValue>.

To see the problem, ask your self: Lets say we have a TValue that serializes in to something that uses Elements it describes itself as XML (lets say a dictionary of dictionaries Dictionary<int,Dictionary<int,string>> (not that uncommon of a pattern, it's a lookup table)), how would your Attribute only version represent a dictionary entirely inside a attribute?