Serialize Dictionary member to XML elements and data

Question

I have a class \'products\' that is serializable to XML. I\'m using the standard System.Xml.Serialization.XmlSerializer to serialize and a XmlWriter \'writer\' object to write t

Answer 1

Assuming that your dictionary value are all simple types that can be converted to a string, you can create your own IXmlSerializable dictionary wrapper to store and retrieve the keys and values:

public class XmlKeyTextValueListWrapper : CollectionWrapper>, IXmlSerializable
{
    public XmlKeyTextValueListWrapper() : base(new List>()) { } // For deserialization.

    public XmlKeyTextValueListWrapper(ICollection> baseCollection) : base(baseCollection) { }

    public XmlKeyTextValueListWrapper(Func>> getCollection) : base(getCollection) {}

    #region IXmlSerializable Members

    public XmlSchema GetSchema()
    {
        return null;
    }

    public void ReadXml(XmlReader reader)
    {
        var converter = TypeDescriptor.GetConverter(typeof(TValue));
        XmlKeyValueListHelper.ReadXml(reader, this, converter);
    }

    public void WriteXml(XmlWriter writer)
    {
        var converter = TypeDescriptor.GetConverter(typeof(TValue));
        XmlKeyValueListHelper.WriteXml(writer, this, converter);
    }

    #endregion
}

public static class XmlKeyValueListHelper
{
    public static void WriteXml(XmlWriter writer, ICollection> collection, TypeConverter typeConverter)
    {
        foreach (var pair in collection)
        {
            writer.WriteStartElement(XmlConvert.EncodeName(pair.Key));
            writer.WriteValue(typeConverter.ConvertToInvariantString(pair.Value));
            writer.WriteEndElement();
        }
    }

    public static void ReadXml(XmlReader reader, ICollection> collection, TypeConverter typeConverter)
    {
        if (reader.IsEmptyElement)
        {
            reader.Read();
            return;
        }

        reader.ReadStartElement(); // Advance to the first sub element of the list element.
        while (reader.NodeType == XmlNodeType.Element)
        {
            var key = XmlConvert.DecodeName(reader.Name);
            string value;
            if (reader.IsEmptyElement)
            {
                value = string.Empty;
                // Move past the end of item element
                reader.Read();
            }
            else
            {
                // Read content and move past the end of item element
                value = reader.ReadElementContentAsString();
            }
            collection.Add(new KeyValuePair(key, (T)typeConverter.ConvertFromInvariantString(value)));
        }
        // Move past the end of the list element
        reader.ReadEndElement();
    }

    public static void CopyTo(this XmlKeyTextValueListWrapper collection, ICollection> dictionary)
    {
        if (dictionary == null)
            throw new ArgumentNullException("dictionary");
        if (collection == null)
            dictionary.Clear();
        else
        {
            if (collection.IsWrapperFor(dictionary)) // For efficiency
                return;
            var pairs = collection.ToList();
            dictionary.Clear();
            foreach (var item in pairs)
                dictionary.Add(item);
        }
    }
}

public class CollectionWrapper : ICollection
{
    readonly Func> getCollection;

    public CollectionWrapper(ICollection baseCollection)
    {
        if (baseCollection == null)
            throw new ArgumentNullException();
        this.getCollection = () => baseCollection;
    }

    public CollectionWrapper(Func> getCollection)
    {
        if (getCollection == null)
            throw new ArgumentNullException();
        this.getCollection = getCollection;
    }

    public bool IsWrapperFor(ICollection other)
    {
        if (other == Collection)
            return true;
        var otherWrapper = other as CollectionWrapper;
        return otherWrapper != null && otherWrapper.IsWrapperFor(Collection);
    }

    ICollection Collection { get { return getCollection(); } }

    #region ICollection Members

    public void Add(T item)
    {
        Collection.Add(item);
    }

    public void Clear()
    {
        Collection.Clear();
    }

    public bool Contains(T item)
    {
        return Collection.Contains(item);
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        Collection.CopyTo(array, arrayIndex);
    }

    public int Count
    {
        get { return Collection.Count; }
    }

    public bool IsReadOnly
    {
        get { return Collection.IsReadOnly; }
    }

    public bool Remove(T item)
    {
        return Collection.Remove(item);
    }

    #endregion

    #region IEnumerable Members

    public IEnumerator GetEnumerator()
    {
        return Collection.GetEnumerator();
    }

    #endregion

    #region IEnumerable Members

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    #endregion
}

And then use it like so:

[XmlRoot("products")]
public class Products
{
    public Products()
    {
        Specifications = new Dictionary();
    }

    [XmlIgnore]
    [JsonProperty("specifications")] // For testing purposes, I compare Json.NET serialization before and after XML serialization.  You can remove this.
    public Dictionary Specifications { get; set; }

    [XmlElement("specifications")]
    [JsonIgnore] // For testing purposes, I compare Json.NET serialization before and after XML serialization.  You can remove this.
    public XmlKeyTextValueListWrapper XmlSpecifications
    {
        get
        {
            return new XmlKeyTextValueListWrapper(() => this.Specifications);
        }
        set
        {
            value.CopyTo(Specifications = (Specifications ?? new Dictionary()));
        }
    }
}

The fact that your dictionary values are simple types (directly convertible from and to text) makes it possible to avoid nested creations of XmlSerializer, which is more complex. See here for an example.