XmlSerializer - There was an error reflecting type

Using C# .NET 2.0, I have a composite data class that does have the [Serializable] attribute on it. I am creating an XMLSerializer class and passing that into the constructor:

XmlSerializer serializer = new XmlSerializer(typeof(DataClass));

I am getting an exception saying:

There was an error reflecting type.

Inside the data class there is another composite object. Does this also need to have the [Serializable] attribute, or by having it on the top object, does it recursively apply it to all objects inside?

Solution 1:

Look at the inner exception that you are getting. It will tell you which field/property it is having trouble serializing.

You can exclude fields/properties from xml serialization by decorating them with the [XmlIgnore] attribute.

XmlSerializer does not use the [Serializable] attribute, so I doubt that is the problem.

Solution 2:

Remember that serialized classes must have default (i.e. parameterless) constructors. If you have no constructor at all, that's fine; but if you have a constructor with a parameter, you'll need to add the default one too.

Solution 3:

I had a similar problem, and it turned out that the serializer could not distinguish between 2 classes I had with the same name (one was a subclass of the other). The inner exception looked like this:

'Types BaseNamespace.Class1' and 'BaseNamespace.SubNamespace.Class1' both use the XML type name, 'Class1', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type.

Where BaseNamespace.SubNamespace.Class1 is a subclass of BaseNamespace.Class1.

What I needed to do was add an attribute to one of the classes (I added to the base class):

[XmlType("BaseNamespace.Class1")]

Note: If you have more layers of classes you need to add an attribute to them as well.

Solution 4:

Most common reasons by me:

 - the object being serialized has no parameterless constructor
 - the object contains Dictionary
 - the object has some public Interface members

Solution 5:

Also be aware that XmlSerializer cannot serialize abstract properties.. See my question here (which I have added the solution code to)..

XML Serialization and Inherited Types