How to serialize a class with a list of custom objects?

Question

I have two classes:

namespace Something
{
    [Serializable]
    public class Spec
    {
        public string Name { get; set; }

        [XmlArray]
        public List<Value> Values { get; set; }
    }

    [Serializable]
    public class Value
    {
        public string Name { get; set; }

        public short StartPosition { get; set; }

        public short EndPosition { get; set; }

        public Value(string name, short startPosition, short endPosition)
        {
            Name = name;
            StartPosition = startPosition;
            EndPosition = endPosition;
        }
    }
}

When I try to serialize

var spec = new Spec();
spec.Name = "test";
spec.Values = new List<Value> { new Value("testing", 0, 2) };

var xmls = new XmlSerializer(spec.GetType());    
xmls.Serialize(Console.Out, spec);

I get an error:

InvalidOperationException

There was an error reflecting type 'Something.Spec'

Using a list of string I don't have any problems. Am I missing some attribute?

Try looking at that exception you get, notice that it says "see inner exception for more details", and the inner exception says: "...Value cannot be serialized because it does not have a parameterless constructor". — Lasse V. Karlsen, Feb 27 '11 at 18:32

score 7 · Accepted Answer · answered Feb 27 '11 at 18:22

7

The Value class needs to have a default constructor if you want it to be serializable. Example:

public class Value
{
    public string Name { get; set; }
    public short StartPosition { get; set; }
    public short EndPosition { get; set; }
}

Also not that you don't need the [Serializable] attribute for XML serialization and it is completely ignored by the XmlSerializer class.

answered Feb 27 '11 at 18:22

Darin Dimitrov

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In fact, the InnerException of the exception he got mentions this particular fact, no parameterless constructor. – Lasse V. Karlsen Feb 27 '11 at 18:32
@Lasse I completely forgot to check the inner exception, thanks. I was testing here, the default constructor needs to exist but it is not used for anything. So I made it thrown an exception, I need the values to be setted, a "default value" is invalid. – BrunoLM Feb 27 '11 at 18:36
thanks for your clear answer and for telling me about the `Serializable` attribute that is not needed by XML serialization. I actually didn't know that. :P – BrunoLM Feb 27 '11 at 18:38
@Bruno: The parameterless constructor will be used on deserialization. – Lasse V. Karlsen Feb 27 '11 at 19:46

score 0 · Answer 2 · answered Feb 27 '11 at 18:23

0

Could it be that your Value type doesn't have a constructor that can be used to create an instance when deserialising?

answered Feb 27 '11 at 18:23

Matthew Abbott

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How to serialize a class with a list of custom objects?

2 Answers2

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