Xml Serialization - System.InvalidOperationException: Is it not possible to serialize 'this'?

Question

Hopefully this question isn't too obvious, however I'm taking my first steps into the topic of serialization and couldn't find an explanation for the following behaviour:

I wanted to serialize a class to test if I set up everything correctly. For this I took the code from this tutorial and adapted it as follows:

    private void SerializePresets(string path)
    {
        XmlSerializer xmlSerializer = new XmlSerializer(typeof(MyClass));
        using (TextWriter writer = new StreamWriter(path))
        {
            xmlSerializer.Serialize(writer, this);
        }
    }

This method lies within MyClass and is also called from there. This gives me the following exception:

An exception of type 'System.InvalidOperationException' occurred in System.Xml.dll but was not handled in user code

Additional information: There was an error reflecting type 'MyClass'.

Since MyClass holds other class object as properties first I thought I have to make those serializabel too, however the exception still persists. So, my guess is, that it is impossible serialize this, however I couldn't find a confirmation to this guess.

EDIT: This property causes the issue according to the inner exception:

[XmlArray("VolumePresetList"), XmlArrayItem(typeof(LinearAxisColorPresetsModel), ElementName = "VolumePresetList")]
public ObservableCollection<LinearAxisColorPresetsModel> VolumePresetList { get; set; }

@spodger I'll try to paste it here, but I have to take a look at it first and rename some things, since it is for a classified project.. — Roland Deschain, Feb 28 '19 at 14:31
The thing is, what you are trying is perfectly possible as long as `MyClass` is defined appropriately. — spodger, Feb 28 '19 at 14:34
@Dirk thanks for the tipp (silly me), found the Property that causes the issue and will edit OP — Roland Deschain, Feb 28 '19 at 14:34
Found the problem and added it as answer, thank you all for the help! — Roland Deschain, Feb 28 '19 at 14:47

score 1 · Answer 1 · answered Feb 28 '19 at 14:26

You can use this. It must be one of the properties like a Dictionary that doesn't serialize. See my example below

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;
using System.Xml.Serialization;
using System.IO;

namespace ConsoleApplication103
{
    class Program
    {

        const string FILENAME = @"c:\temp\test.xml";
        static void Main(string[] args)
        {
            MyClass myClass = new MyClass();
            myClass.Serialize(FILENAME);

        }
    }
    public class MyClass
    {
         public string test { get; set; }

         public void Serialize(string filename)
         {
             SerializePresets(filename);
         }
         private void SerializePresets(string path)
         {
             XmlSerializer xmlSerializer = new XmlSerializer(typeof(MyClass));
             using (TextWriter writer = new StreamWriter(path))
             {
                 xmlSerializer.Serialize(writer, this);
             }
        }
    }

}

Is there a way to find out which of the properties causes the issue? — Roland Deschain, Feb 28 '19 at 14:29
I usually comment out properties until I find the one causing the issue. I do not think you StackTrace exception message will help, but you can try. — jdweng, Feb 28 '19 at 14:40

score 1 · Accepted Answer · answered Feb 28 '19 at 14:46

1

With the help of the inner exceptions (thanks for the tip again) I could find out the reason why the serialization failed.

The class LinearAxisColorPresetsModeldid not have a parameterless Constructor, which caused this issue.

Simply adding

/// <summary>
/// Default Constructor
/// </summary>
private LinearAxisColorPresetsModel()
{

}

to this class solved the problem for me. What remains is to find out the reason, why we must have a parameterless Constructor.

EDIT: Found the reasoning behind this behaviour in this post.

answered Feb 28 '19 at 14:46

Roland Deschain

2,211
19
50

Interestingly Boost serialisation for C++ also needs classes to have a parameterless constructor. In that it's because deserialisation works in a similar way to that described in the link you've added. I guess this is necessary for serialisation that is not an inherent part of the language (XML for C#, Boost for C++); as a library it has no knowledge of how an object get layed out in memory, and so has use the constructor to create it. At least in C# the setters can do useful things. In C++ there are no setters, and so post-deserialisation work has to be called manually; room for errors... – bazza Mar 01 '19 at 21:16

Xml Serialization - System.InvalidOperationException: Is it not possible to serialize 'this'?

2 Answers2