Generic List XML Serialization with different classes

Question

I have got the following code:

BaseContent.cs

public class BaseContent
{
   // Some auto properties
}

News.cs

public class News : BaseContent
{
   // Some more auto properties
}

Events.cs

public class Event : BaseContent
{
   // Some more auto properites
}

GenericResponse.cs

public class GenericResponse<T> 
{
  [XmlArray("Content")]
  [XmlArrayItem("NewsObject", typeof(News)]
  [XmlArrayItem("EventObject", typeof(Event)]
  public List<T> ContentItems { get; set; }
}

NewsResponse.cs

public class NewsResponse : GenericResponse<News> {}

EventResponse.cs

public class EventResponse : GenericResponse<Event> {}

As you can see, I have a base class BaseContent and two classes deriving from it. Next I have a generic response class, since the structure of the xml-files is always the same, but they differ in some properties.

I thought I can specify with the [XmlArrayItem] which name to use for a specific class. But now I get the error:

System.InvalidOperationException: Unable to generate a temporary class (result=1). error CS0012: The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

I can not add this reference, because I'm working on a Windows 8 App.

If I comment out one of the [XmlArrayItem] it is working well.

Anyone got an idea to solve this problem?

Update I can not use DataContractSerializer, because I have to use XmlAttributes

Answer 1

Edit: Feel free to download the demo project

You didn't provide all the properties for the objects, so allow me to add some - just as an example:

public class BaseContent
{
    [XmlAttribute("Name")]
    public string Name { get; set; }
}

[XmlType(TypeName = "EventObject")]
public class Event : BaseContent
{
    [XmlAttribute("EventId")]
    public int EventId { get; set; }
}

[XmlType(TypeName = "NewsObject")]
public class News : BaseContent
{
    [XmlAttribute("NewsId")]
    public int NewsId { get; set; }
}

GenericResponse.cs could be defined this way - no need to specify the typeof for the array items:

public class GenericResponse<T>
{
    [XmlArray("Content")]
    public List<T> ContentItems { get; set; }

    public GenericResponse()
    {
        this.ContentItems = new List<T>();
    }
}

And then you have the response classes:

public class EventResponse : GenericResponse<Event>
{
}

public class NewsResponse : GenericResponse<News>
{
}

Example 1: Serialize an EventResponse object

var response = new EventResponse
{
    ContentItems = new List<Event> 
    {
        new Event {
            EventId = 1,
            Name = "Event 1"
        },

        new Event {
            EventId = 2,
            Name = "Event 2"
        }
    }
};

string xml = XmlSerializer<EventResponse>.Serialize(response);

Output XML:

<?xml version="1.0" encoding="utf-8"?>
<EventResponse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Content>
        <EventObject Name="Event 1" EventId="1" />
        <EventObject Name="Event 2" EventId="2" />
    </Content>
</EventResponse>

If you try the same with NewsResponse it will work fine. BTW I'm using my generic XmlSerializer, click on the link to know more about it.

XmlSerializer.cs:

/// <summary>
/// XML serializer helper class. Serializes and deserializes objects from/to XML
/// </summary>
/// <typeparam name="T">The type of the object to serialize/deserialize.
/// Must have a parameterless constructor and implement <see cref="Serializable"/></typeparam>
public class XmlSerializer<T> where T: class, new()
{
    /// <summary>
    /// Deserializes a XML string into an object
    /// Default encoding: <c>UTF8</c>
    /// </summary>
    /// <param name="xml">The XML string to deserialize</param>
    /// <returns>An object of type <c>T</c></returns>
    public static T Deserialize(string xml)
    {
        return Deserialize(xml, Encoding.UTF8, null);
    }

    /// <summary>
    /// Deserializes a XML string into an object
    /// Default encoding: <c>UTF8</c>
    /// </summary>
    /// <param name="xml">The XML string to deserialize</param>
    /// <param name="encoding">The encoding</param>
    /// <returns>An object of type <c>T</c></returns>
    public static T Deserialize(string xml, Encoding encoding)
    {
        return Deserialize(xml, encoding, null);
    }

    /// <summary>
    /// Deserializes a XML string into an object
    /// </summary>
    /// <param name="xml">The XML string to deserialize</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlReaderSettings"/></param>
    /// <returns>An object of type <c>T</c></returns>
    public static T Deserialize(string xml, XmlReaderSettings settings)
    {
        return Deserialize(xml, Encoding.UTF8, settings);
    }

    /// <summary>
    /// Deserializes a XML string into an object
    /// </summary>
    /// <param name="xml">The XML string to deserialize</param>
    /// <param name="encoding">The encoding</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlReaderSettings"/></param>
    /// <returns>An object of type <c>T</c></returns>
    public static T Deserialize(string xml, Encoding encoding, XmlReaderSettings settings)
    {
        if (string.IsNullOrEmpty(xml))
            throw new ArgumentException("XML cannot be null or empty", "xml");

        XmlSerializer xmlSerializer = new XmlSerializer(typeof(T));

        using (MemoryStream memoryStream = new MemoryStream(encoding.GetBytes(xml)))
        {
            using (XmlReader xmlReader = XmlReader.Create(memoryStream, settings))
            {
                return (T) xmlSerializer.Deserialize(xmlReader);
            }
        }
    }

    /// <summary>
    /// Deserializes a XML file.
    /// </summary>
    /// <param name="filename">The filename of the XML file to deserialize</param>
    /// <returns>An object of type <c>T</c></returns>
    public static T DeserializeFromFile(string filename)
    {
        return DeserializeFromFile(filename, new XmlReaderSettings());
    }

    /// <summary>
    /// Deserializes a XML file.
    /// </summary>
    /// <param name="filename">The filename of the XML file to deserialize</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlReaderSettings"/></param>
    /// <returns>An object of type <c>T</c></returns>
    public static T DeserializeFromFile(string filename, XmlReaderSettings settings)
    {
        if (string.IsNullOrEmpty(filename))
            throw new ArgumentException("filename", "XML filename cannot be null or empty");

        if (! File.Exists(filename))
            throw new FileNotFoundException("Cannot find XML file to deserialize", filename);

        // Create the stream writer with the specified encoding
        using (XmlReader reader = XmlReader.Create(filename, settings))
        {
            System.Xml.Serialization.XmlSerializer xmlSerializer = new System.Xml.Serialization.XmlSerializer(typeof(T));
            return (T) xmlSerializer.Deserialize(reader);
        }
    }

    /// <summary>
    /// Serialize an object
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <returns>A XML string that represents the object to be serialized</returns>
    public static string Serialize(T source)
    {
        // indented XML by default
        return Serialize(source, null, GetIndentedSettings());
    }

    /// <summary>
    /// Serialize an object
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="namespaces">Namespaces to include in serialization</param>
    /// <returns>A XML string that represents the object to be serialized</returns>
    public static string Serialize(T source, XmlSerializerNamespaces namespaces)
    {
        // indented XML by default
        return Serialize(source, namespaces, GetIndentedSettings());
    }

    /// <summary>
    /// Serialize an object
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlWriterSettings"/></param>
    /// <returns>A XML string that represents the object to be serialized</returns>
    public static string Serialize(T source, XmlWriterSettings settings)
    {
        return Serialize(source, null, settings);
    }

    /// <summary>
    /// Serialize an object
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="namespaces">Namespaces to include in serialization</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlWriterSettings"/></param>
    /// <returns>A XML string that represents the object to be serialized</returns>
    public static string Serialize(T source, XmlSerializerNamespaces namespaces, XmlWriterSettings settings)
    {
        if (source == null)
            throw new ArgumentNullException("source", "Object to serialize cannot be null");

        string xml = null;
        XmlSerializer serializer = new XmlSerializer(source.GetType());

        using (MemoryStream memoryStream = new MemoryStream())
        {
            using (XmlWriter xmlWriter = XmlWriter.Create(memoryStream, settings))
            {
                System.Xml.Serialization.XmlSerializer x = new System.Xml.Serialization.XmlSerializer(typeof(T));
                x.Serialize(xmlWriter, source, namespaces);

                memoryStream.Position = 0; // rewind the stream before reading back.
                using (StreamReader sr = new StreamReader(memoryStream))
                {
                    xml = sr.ReadToEnd();
                } 
            }
        }

        return xml;
    }

    /// <summary>
    /// Serialize an object to a XML file
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="filename">The file to generate</param>
    public static void SerializeToFile(T source, string filename)
    {
        // indented XML by default
        SerializeToFile(source, filename, null, GetIndentedSettings());
    }

    /// <summary>
    /// Serialize an object to a XML file
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="filename">The file to generate</param>
    /// <param name="namespaces">Namespaces to include in serialization</param>
    public static void SerializeToFile(T source, string filename, XmlSerializerNamespaces namespaces)
    {
        // indented XML by default
        SerializeToFile(source, filename, namespaces, GetIndentedSettings());
    }

    /// <summary>
    /// Serialize an object to a XML file
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="filename">The file to generate</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlWriterSettings"/></param>
    public static void SerializeToFile(T source, string filename, XmlWriterSettings settings)
    {
         SerializeToFile(source, filename, null, settings);
    }

    /// <summary>
    /// Serialize an object to a XML file
    /// </summary>
    /// <param name="source">The object to serialize</param>
    /// <param name="filename">The file to generate</param>
    /// <param name="namespaces">Namespaces to include in serialization</param>
    /// <param name="settings">XML serialization settings. <see cref="System.Xml.XmlWriterSettings"/></param>
    public static void SerializeToFile(T source, string filename, XmlSerializerNamespaces namespaces, XmlWriterSettings settings)
    {
        if (source == null)
            throw new ArgumentNullException("source", "Object to serialize cannot be null");

        XmlSerializer serializer = new XmlSerializer(source.GetType());

        using (XmlWriter xmlWriter = XmlWriter.Create(filename, settings))
        {
            System.Xml.Serialization.XmlSerializer x = new System.Xml.Serialization.XmlSerializer(typeof(T));
            x.Serialize(xmlWriter, source, namespaces);
        }
    }

    #region Private methods


    private static XmlWriterSettings GetIndentedSettings()
    {
        XmlWriterSettings xmlWriterSettings = new XmlWriterSettings();
        xmlWriterSettings.Indent = true;
        xmlWriterSettings.IndentChars = "\t";

        return xmlWriterSettings;
    }

    #endregion
}

Answer 2

I found my solution. No the best, but it is working.

I impleted IXmlSerializable and handeled the stuff by myself:

public void ReadXml(System.Xml.XmlReader reader)
{
    reader.Read();
    reader.MoveToContent();

    if (reader.LocalName == "AnotherNode")
    {
        var innerXml = Serializer<AnotherClass>.CreateSerializer();
        Remove = (AnotherClass) innerXml.Deserialize(reader);
        reader.MoveToContent();
    }

    reader.Read();

    // Here is the trick
    if (reader.IsStartElement())
    {
        do
        {
            var innerXml = Serializer<T>.CreateSerializer();

            var obj = (T) innerXml.Deserialize(reader);
            Updates.Add(obj);
        } while (reader.MoveToContent() == XmlNodeType.Element);
    }
}

public void WriteXml(System.Xml.XmlWriter writer)
{
    var removeSerializer = Serializer<RemoveElement>.CreateSerializer();
    removeSerializer.Serialize(writer, Remove);

    if (Updates.Any())
    {
        var innerXml = Serializer<T>.CreateSerializer();
        writer.WriteStartElement("ContentUpdates");
        foreach (var update in Updates)
        {
            innerXml.Serialize(writer, update);
        }
        writer.WriteEndElement();
    }
}