Serialize Class containing Dictionary member

Question

Expanding upon my earlier problem, I've decided to (de)serialize my ConfigFile 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();
            }
        }
    }
}

Answer 1

Dictionaries and Hashtables are not serializable with XmlSerializer. Therefore you cannot use them directly. A workaround would be to use the XmlIgnore attribute to hide those properties from the serializer and expose them via a list of serializable key-value pairs.

PS: constructing an XmlSerializer is very expensive, so always cache it if there is a chance of being able to re-use it.

Answer 2

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.

Answer 3

This article explains exactly how to handle this: How do I... Serialize a hash table in C# when the application requires it?

I hope this is helpful

Answer 4

There is a solution here http://weblogs.asp.net/pwelter34/archive/2006/05/03/444961.aspx