Serialize Class containing Dictionary member


Question

Expanding upon my earlier problem, I've decided to (de)serialize my config file class which worked great.

I now want to store an associative array of drive letters to map (key is the drive letter, value is the network path) and have tried using Dictionary, HybridDictionary, and Hashtable for this but I always get the following error when calling ConfigFile.Load() or ConfigFile.Save():

There was an error reflecting type 'App.ConfigFile'. [snip] System.NotSupportedException: Cannot serialize member App.Configfile.mappedDrives [snip]

From what I've read Dictionaries and HashTables can be serialized, so what am I doing wrong?

[XmlRoot(ElementName="Config")]
public class ConfigFile
{
    public String guiPath { get; set; }
    public string configPath { get; set; }
    public Dictionary<string, string> mappedDrives = new Dictionary<string, string>();

    public Boolean Save(String filename)
    {
        using(var filestream = File.Open(filename, FileMode.OpenOrCreate,FileAccess.ReadWrite))
        {
            try
            {
                var serializer = new XmlSerializer(typeof(ConfigFile));
                serializer.Serialize(filestream, this);
                return true;
            } catch(Exception e) {
                MessageBox.Show(e.Message);
                return false;
            }
        }
    }

    public void addDrive(string drvLetter, string path)
    {
        this.mappedDrives.Add(drvLetter, path);
    }

    public static ConfigFile Load(string filename)
    {
        using (var filestream = File.Open(filename, FileMode.Open, FileAccess.Read))
        {
            try
            {
                var serializer = new XmlSerializer(typeof(ConfigFile));
                return (ConfigFile)serializer.Deserialize(filestream);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message + ex.ToString());
                return new ConfigFile();
            }
        }
    }
}
1
132
5/23/2017 10:31:38 AM

Accepted Answer

You can't serialize a class that implements IDictionary. Check out this link.

Q: Why can't I serialize hashtables?

A: The XmlSerializer cannot process classes implementing the IDictionary interface. This was partly due to schedule constraints and partly due to the fact that a hashtable does not have a counterpart in the XSD type system. The only solution is to implement a custom hashtable that does not implement the IDictionary interface.

So I think you need to create your own version of the Dictionary for this. Check this other question.

70
5/23/2017 11:47:32 AM

There is a solution at Paul Welter's Weblog - XML Serializable Generic Dictionary

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 serialzable 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
{
    public SerializableDictionary() { }
    public SerializableDictionary(IDictionary<TKey, TValue> dictionary) : base(dictionary) { }
    public SerializableDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer) : base(dictionary, comparer) { }
    public SerializableDictionary(IEqualityComparer<TKey> comparer) : base(comparer) { }
    public SerializableDictionary(int capacity) : base(capacity) { }
    public SerializableDictionary(int capacity, IEqualityComparer<TKey> comparer) : base(capacity, comparer) { }

    #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
}

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