C# Xml serialization, collection and root element

Question

My app serializes objects in streams. Here is a sample of what I need :

Answer 1

Ok, here is my final solution (hope it helps someone), that can serialize a plain array, List<>, HashSet<>, ...

To achieve this, we'll need to tell the serializer what root node to use, and it's kind of tricky...

1) Use 'XmlType' on the serializable object

[XmlType("link")]
public class LinkFinalVersion
{
    [XmlAttribute("href")]
    public string Url { get; set; }

    [XmlAttribute("rel")]
    public string Relationship { get; set; }
}

2) Code a 'smart-root-detector-for-collection' method, that will return a XmlRootAttribute

private XmlRootAttribute XmlRootForCollection(Type type)
{
    XmlRootAttribute result = null;

    Type typeInner = null;
    if(type.IsGenericType)
    {
        var typeGeneric = type.GetGenericArguments()[0];
        var typeCollection = typeof (ICollection<>).MakeGenericType(typeGeneric);
        if(typeCollection.IsAssignableFrom(type))
            typeInner = typeGeneric;
    }
    else if(typeof (ICollection).IsAssignableFrom(type)
        && type.HasElementType)
    {
        typeInner = type.GetElementType();
    }

    // yeepeeh ! if we are working with a collection
    if(typeInner != null)
    {
        var attributes = typeInner.GetCustomAttributes(typeof (XmlTypeAttribute), true);
        if((attributes != null)
            && (attributes.Length > 0))
        {
            var typeName = (attributes[0] as XmlTypeAttribute).TypeName + 's';
            result = new XmlRootAttribute(typeName);
        }
    }
    return result;
}

3) Push that XmlRootAttribute into the serializer

// hack : get the XmlRootAttribute if the item is a collection
var root = XmlRootForCollection(type);
// create the serializer
var serializer = new XmlSerializer(type, root);

I told you it was tricky ;)

---

To improve this, you can :

A) Create a XmlTypeInCollectionAttribute to specify a custom root name (If the basic pluralization does not fit your need)

[XmlType("link")]
[XmlTypeInCollection("links")]
public class LinkFinalVersion
{
}

B) If possible, cache your XmlSerializer (in a static Dictionary for example).

In my testing, instanciating a XmlSerializer without the XmlRootAttributes takes 3ms. If you specify an XmlRootAttribute, it takes around 80ms (Just to have a custom root node name !)