How to Serialize a Dictionary Member in a Class for Configuration Files?

Serialize a class containing dictionary members

When trying to serialize a class that contains dictionary members (such as a configuration file class), you may encounter the following error:

<code>System.NotSupportedException: 无法序列化成员 App.Configfile.mappedDrives</code>

This error means that by default, the Dictionary type cannot be serialized directly. To resolve this issue, consider implementing a custom serialization mechanism.

Custom dictionary serialization

One way is to create a custom class that inherits from Dictionary<TKey, TValue> and implements the IXmlSerializable interface. The following code snippet demonstrates this implementation:

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

[XmlRoot("dictionary")]
public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IXmlSerializable
{
    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();
        }
    }
}

Custom dictionaries can participate in XML serialization by implementing IXmlSerializable.

Usage

Once a custom dictionary is defined, it can be used to store the required key-value pairs in the profile class:

public class ConfigFile
{
    ...
    public SerializableDictionary<string, string> mappedDrives = new SerializableDictionary<string, string>();
    ...
}

With this approach, configuration file classes can be serialized and deserialized without encountering serialization errors.

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