C# generic serialization utility class

Question

I have an existing class for serializing and deserializing objects to/from XML. It's a generic class with a single type parameter T whose only constraint is where T : IXmlSerializable. However, I want to still be able to use this class on classes that do not implement IXmlSerializable but have the [Serializable] attribute. How could I go about doing this?

From my generic class:

public static class XmlSerializationUtils<T> where T : IXmlSerializable
{
    public static T DeserializeXml(XmlDocument xml) { ... }
    public static XmlDocument SerializeToXml(T toSerialize) { ... }
}

I found this discussion but there was no solution given, just that I can't do where T : Serializable. Trying to do where T : SerializableAttribute makes Visual Studio say "Cannot use sealed class 'System.SerializableAttribute' as type parameter constraint".

Edit: based on Stephen's answer, I removed the constraints on XmlSerializationUtils<T> and added this static constructor:

static XmlSerializationUtils()
{
    Type type = typeof(T);
    bool hasAttribute = null != Attribute.GetCustomAttribute(type,
        typeof(SerializableAttribute));
    bool implementsInterface =
        null != type.GetInterface(typeof(IXmlSerializable).FullName);
    if (!hasAttribute && !implementsInterface)
    {
        throw new ArgumentException(
            "Cannot use XmlSerializationUtils on class " + type.Name +
            " because it does not have the Serializable attribute " +
            " and it does not implement IXmlSerializable"
        );
    }
}

Answer 1

You can't require an attribute as part of generics. However, you could provide a static constructor that checks for it and throws if it's not found.

Answer 2

I'd just eliminate the type constraint and catch the SerializationException when the type does not serialize or deserialize properly... In fact, this allows your generic Serialize and Deserialize methods to accept a formatter

public enum Formatter { Binary, Xml }

that could control whether the serialization is binary or Xml

public class Serialization
{
    public enum Formatter { Binary, Xml }

    #region Serialization methods
    public static void Serialize2File<T>(T obj, string pathSpec, 
        Formatter formatter)
    {
        try
        {
            switch (formatter)
            {
                case (Formatter.Binary):
                    using (var fs = new FileStream(pathSpec, FileMode.Create,
                                        FileAccess.Write, FileShare.Write))
                        (new BinaryFormatter()).Serialize(fs, obj);
                    break;

                case (Formatter.Xml):
                    var serializer = new XmlSerializer(typeof(T));
                    TextWriter textWriter = new StreamWriter(pathSpec);
                    serializer.Serialize(textWriter, obj);
                    textWriter.Close();
                    break;

                default:
                    throw new MyCustomException("Invalid Formatter option");
            }
        }
        catch (SerializationException sX)
        {
            var errMsg = String.Format(
                "Unable to serialize {0} into file {1}",
                obj, pathSpec);
            throw new MyCustomException(errMsg, sX);
        }
    }
    public static T DeSerializeFromFile<T>(string pathSpec, 
        Formatter formatter) where T : class
    {
        try
        {
            switch (formatter)
            {
                case (Formatter.Binary):
                    using (var strm = new FileStream(pathSpec,
                                        FileMode.Open, FileAccess.Read))
                    {
                        IFormatter fmt = new BinaryFormatter();
                        var o = fmt.Deserialize(strm);
                        if (!(o is T))
                            throw new ArgumentException("Bad Data File");
                        return o as T;
                    }

                case (Formatter.Xml):
                    var serializer = new XmlSerializer(typeof(T));
                    TextReader rdr = new StreamReader(pathSpec);
                    return (T)serializer.Deserialize(rdr);

                default:
                    throw new MyCustomException("Invalid Formatter option");
            }
        }
        catch (SerializationException sX)
        {
            var errMsg = String.Format(
                "Unable to deserialize {0} from file {1}",
                typeof(T), pathSpec);
            throw new MyCustomException(errMsg, sX);
        }
    }
    #endregion Serialization methods
}

Answer 3

You can check to see if a type is serializable using the IsSerializable property of the Type of the object.

myObj.GetType().IsSerializable

As mentioned, this isn't possible to add as a generic constraint, but would most likely be checked in a constructor.