How to XML serialize an array of Lists of objects?

Question

I am trying to save an array of lists of an object in C# with in a xml file. I succeeded to save a array of an object and a list of objects but not an array of lists of an object.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace expirement
{
    public class Box
    {
        public int x;
        public Box(int a)
        {
            x = a;
        }
        public Box()
        {
        }
    }

    public class Program
    {
        static void Main(string[] args)
        {
            List<Box>[] MainArr = new List<Box>[1];
            MainArr[0] = new List<Box>();
            Box Box1 = new Box(1);
            MainArr[0].Add(Box1);
            System.Xml.Serialization.XmlSerializer writer = new System.Xml.Serialization.XmlSerializer(MainArr.GetType());
            System.IO.StreamWriter fileWrite = new System.IO.StreamWriter(@"C:\Users\student\Desktop\ArrListBox.xml");
            writer.Serialize(fileWrite,MainArr);
            fileWrite.Close();
        }
    }
}

i get the error:

Unable to generate a temporary class (result=1).
error CS1026: ) expected
error CS1002: ; expected 
error CS1525: Invalid expression term ')'
error CS1002: ; expected
error CS1525: Invalid expression term ')'

Answer 1

I reproduced your error message and found it is indeed a bug in the XML serializer from Microsoft.

When using the XmlSerializer(type) constructor, .NET automatically generates an assembly called AssemblyName.XmlSerializer.dll . This assembly contains the actual classes that do the serialization and deserialization of your code.

When running this in an empty console application, I first got a NullReferenceException like a few others commenting. When I was experimenting with self-generating the assembly using sgen , I did get reasonable code when using a class deriving from List<List<Box>> (you can only pre-compile classes, so you can't pre-compile a serializer for List<Box>[] ).

I finally got your error message when using this class, which is possibly one of your test classes in your project:

public class X
{
    public List<Box>[] Boxes { get; set; }
}

Using sgen :

"C:\Program Files (x86)\Microsoft SDKs\Windows\v8.1A\bin\NETFX 4.5.1 Tools\sgen" /t:"expirement.X" /a:ConsoleApplication8.exe /force

This gives me the same error as you. Unfortunately, there is no quick fix. Using another type seems to do the trick. Report this issue at Microsoft Connect.

---

As a reference, this is the full code of the serialization (using switch /k in sgen ). The code seems so broken, I couldn't quick fix it:

#if _DYNAMIC_XMLSERIALIZER_COMPILATION
[assembly:System.Security.AllowPartiallyTrustedCallers()]
[assembly:System.Security.SecurityTransparent()]
[assembly:System.Security.SecurityRules(System.Security.SecurityRuleSet.Level1)]
#endif
[assembly: System.Reflection.AssemblyVersionAttribute("1.0.0.0")]
[assembly: System.Xml.Serialization.XmlSerializerVersionAttribute(ParentAssemblyId = @"c80da358-347f-48cf-88a7-0fda1a15c25b,", Version = @"4.0.0.0")]
namespace Microsoft.Xml.Serialization.GeneratedAssembly
{

    public class XmlSerializationWriterX : System.Xml.Serialization.XmlSerializationWriter
    {

        public void Write4_X(object o)
        {
            WriteStartDocument();
            if (o == null)
            {
                WriteNullTagLiteral(@"X", @"");
                return;
            }
            TopLevelElement();
            Write3_X(@"X", @"", ((global::expirement.X)o), true, false);
        }

        void Write3_X(string n, string ns, global::expirement.X o, bool isNullable, bool needType)
        {
            if ((object)o == null)
            {
                if (isNullable) WriteNullTagLiteral(n, ns);
                return;
            }
            if (!needType)
            {
                System.Type t = o.GetType();
                if (t == typeof(global::expirement.X))
                {
                }
                else
                {
                    throw CreateUnknownTypeException(o);
                }
            }
            WriteStartElement(n, ns, o, false, null);
            if (needType) WriteXsiType(@"X", @"");
            {
                global::System.Collections.Generic.List<global::expirement.Box>[] a = (global::System.Collections.Generic.List<global::expirement.Box>[])((global::System.Collections.Generic.List<global::expirement.Box>[])o.@Boxes);
                if (a != null)
                {
                    WriteStartElement(@"Boxes", @"", null, false);
                    for (int ia = 0; ia < a.Length; ia++)
                    {
                        {
                            global::System.Collections.Generic.List<global::expirement.Box> aa = (global::System.Collections.Generic.List<global::expirement.Box>)((global::System.Collections.Generic.List<global::expirement.Box>)a[ia]);
                            if ((object)(aa) == null)
                            {
                                WriteNullTagLiteral(@"ArrayOfBox", @"");
                            }
                            else
                            {
                                WriteStartElement(@"ArrayOfBox", @"", null, false);
                                for (int iaa = 0; iaa < ((System.Collections.ICollection)aa).Count; iaa++)
                                {
                                    Write2_Box(@"Box", @"", ((global::expirement.Box)aa[iaa]), true, false);
                                }
                                WriteEndElement();
                            }
                        }
                    }
                    WriteEndElement();
                }
            }
            WriteEndElement(o);
        }

        void Write2_Box(string n, string ns, global::expirement.Box o, bool isNullable, bool needType)
        {
            if ((object)o == null)
            {
                if (isNullable) WriteNullTagLiteral(n, ns);
                return;
            }
            if (!needType)
            {
                System.Type t = o.GetType();
                if (t == typeof(global::expirement.Box))
                {
                }
                else
                {
                    throw CreateUnknownTypeException(o);
                }
            }
            WriteStartElement(n, ns, o, false, null);
            if (needType) WriteXsiType(@"Box", @"");
            WriteElementStringRaw(@"x", @"", System.Xml.XmlConvert.ToString((global::System.Int32)((global::System.Int32)o.@x)));
            WriteEndElement(o);
        }

        protected override void InitCallbacks()
        {
        }
    }

    public class XmlSerializationReaderX : System.Xml.Serialization.XmlSerializationReader
    {

        public object Read4_X()
        {
            object o = null;
            Reader.MoveToContent();
            if (Reader.NodeType == System.Xml.XmlNodeType.Element)
            {
                if (((object)Reader.LocalName == (object)id1_X && (object)Reader.NamespaceURI == (object)id2_Item))
                {
                    o = Read3_X(true, true);
                }
                else
                {
                    throw CreateUnknownNodeException();
                }
            }
            else
            {
                UnknownNode(null, @":X");
            }
            return (object)o;
        }

        global::expirement.X Read3_X(bool isNullable, bool checkType) {
            System.Xml.XmlQualifiedName xsiType = checkType ? GetXsiType() : null;
            bool isNull = false;
            if (isNullable) isNull = ReadNull();
            if (checkType) {
            if (xsiType == null || ((object) ((System.Xml.XmlQualifiedName)xsiType).Name == (object)id1_X && (object) ((System.Xml.XmlQualifiedName)xsiType).Namespace == (object)id2_Item)) {
            }
            else
                throw CreateUnknownTypeException((System.Xml.XmlQualifiedName)xsiType);
            }
            if (isNull) return null;
            global::expirement.X o;
            o = new global::expirement.X();
            global::System.Collections.Generic.List<global::expirement.Box>[] a_0 = null;
            int ca_0 = 0;
            bool[] paramsRead = new bool[1];
            while (Reader.MoveToNextAttribute()) {
                if (!IsXmlnsAttribute(Reader.Name)) {
                    UnknownNode((object)o);
                }
            }
            Reader.MoveToElement();
            if (Reader.IsEmptyElement) {
                Reader.Skip();
                return o;
            }
            Reader.ReadStartElement();
            Reader.MoveToContent();
            int whileIterations0 = 0;
            int readerCount0 = ReaderCount;
            while (Reader.NodeType != System.Xml.XmlNodeType.EndElement && Reader.NodeType != System.Xml.XmlNodeType.None) {
                if (Reader.NodeType == System.Xml.XmlNodeType.Element) {
                    if (((object) Reader.LocalName == (object)id3_Boxes && (object) Reader.NamespaceURI == (object)id2_Item)) {
                        if (!ReadNull()) {
                            global::System.Collections.Generic.List<global::expirement.Box>[] a_0_0 = null;
                            int ca_0_0 = 0;
                            if ((Reader.IsEmptyElement)) {
                                Reader.Skip();
                            }
                            else {
                                Reader.ReadStartElement();
                                Reader.MoveToContent();
                                int whileIterations1 = 0;
                                int readerCount1 = ReaderCount;
                                while (Reader.NodeType != System.Xml.XmlNodeType.EndElement && Reader.NodeType != System.Xml.XmlNodeType.None) {
                                    if (Reader.NodeType == System.Xml.XmlNodeType.Element) {
                                        if (((object) Reader.LocalName == (object)id4_ArrayOfBox && (object) Reader.NamespaceURI == (object)id2_Item)) {
                                            if (!ReadNull()) {
                                                if ((object)(a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++]) == null) a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++] = new global::System.Collections.Generic.List<global::expirement.Box>();
                                                global::System.Collections.Generic.List<global::expirement.Box> a_0_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>)a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++];
                                                if ((Reader.IsEmptyElement)) {
                                                    Reader.Skip();
                                                }
                                                else {
                                                    Reader.ReadStartElement();
                                                    Reader.MoveToContent();
                                                    int whileIterations2 = 0;
                                                    int readerCount2 = ReaderCount;
                                                    while (Reader.NodeType != System.Xml.XmlNodeType.EndElement && Reader.NodeType != System.Xml.XmlNodeType.None) {
                                                        if (Reader.NodeType == System.Xml.XmlNodeType.Element) {
                                                            if (((object) Reader.LocalName == (object)id5_Box && (object) Reader.NamespaceURI == (object)id2_Item)) {
                                                                if ((object)(a_0_0_0) == null) Reader.Skip(); else a_0_0_0.Add(Read2_Box(true, true));
                                                            }
                                                            else {
                                                                UnknownNode(null, @":Box");
                                                            }
                                                        }
                                                        else {
                                                            UnknownNode(null, @":Box");
                                                        }
                                                        Reader.MoveToContent();
                                                        CheckReaderCount(ref whileIterations2, ref readerCount2);
                                                    }
                                                ReadEndElement();
                                                }
                                            }
                                            else {
                                                if ((object)(a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++]) == null) a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++] = new global::System.Collections.Generic.List<global::expirement.Box>();
                                                global::System.Collections.Generic.List<global::expirement.Box> a_0_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>)a_0_0 = (global::System.Collections.Generic.List<global::expirement.Box>[])EnsureArrayIndex(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>));a_0_0[ca_0_0++];
                                            }
                                        }
                                        else {
                                            UnknownNode(null, @":ArrayOfBox");
                                        }
                                    }
                                    else {
                                        UnknownNode(null, @":ArrayOfBox");
                                    }
                                    Reader.MoveToContent();
                                    CheckReaderCount(ref whileIterations1, ref readerCount1);
                                }
                            ReadEndElement();
                            }
                            o.@Boxes = (global::System.Collections.Generic.List<global::expirement.Box>[])ShrinkArray(a_0_0, ca_0_0, typeof(global::System.Collections.Generic.List<global::expirement.Box>), false);
                        }
                    }
                    else {
                        UnknownNode((object)o, @":Boxes");
                    }
                }
                else {
                    UnknownNode((object)o, @":Boxes");
                }
                Reader.MoveToContent();
                CheckReaderCount(ref whileIterations0, ref readerCount0);
            }
            ReadEndElement();
            return o;
        }

        global::expirement.Box Read2_Box(bool isNullable, bool checkType)
        {
            System.Xml.XmlQualifiedName xsiType = checkType ? GetXsiType() : null;
            bool isNull = false;
            if (isNullable) isNull = ReadNull();
            if (checkType)
            {
                if (xsiType == null || ((object)((System.Xml.XmlQualifiedName)xsiType).Name == (object)id5_Box && (object)((System.Xml.XmlQualifiedName)xsiType).Namespace == (object)id2_Item))
                {
                }
                else
                    throw CreateUnknownTypeException((System.Xml.XmlQualifiedName)xsiType);
            }
            if (isNull) return null;
            global::expirement.Box o;
            o = new global::expirement.Box();
            bool[] paramsRead = new bool[1];
            while (Reader.MoveToNextAttribute())
            {
                if (!IsXmlnsAttribute(Reader.Name))
                {
                    UnknownNode((object)o);
                }
            }
            Reader.MoveToElement();
            if (Reader.IsEmptyElement)
            {
                Reader.Skip();
                return o;
            }
            Reader.ReadStartElement();
            Reader.MoveToContent();
            int whileIterations3 = 0;
            int readerCount3 = ReaderCount;
            while (Reader.NodeType != System.Xml.XmlNodeType.EndElement && Reader.NodeType != System.Xml.XmlNodeType.None)
            {
                if (Reader.NodeType == System.Xml.XmlNodeType.Element)
                {
                    if (!paramsRead[0] && ((object)Reader.LocalName == (object)id6_x && (object)Reader.NamespaceURI == (object)id2_Item))
                    {
                        {
                            o.@x = System.Xml.XmlConvert.ToInt32(Reader.ReadElementString());
                        }
                        paramsRead[0] = true;
                    }
                    else
                    {
                        UnknownNode((object)o, @":x");
                    }
                }
                else
                {
                    UnknownNode((object)o, @":x");
                }
                Reader.MoveToContent();
                CheckReaderCount(ref whileIterations3, ref readerCount3);
            }
            ReadEndElement();
            return o;
        }

        protected override void InitCallbacks()
        {
        }

        string id5_Box;
        string id3_Boxes;
        string id1_X;
        string id2_Item;
        string id6_x;
        string id4_ArrayOfBox;

        protected override void InitIDs()
        {
            id5_Box = Reader.NameTable.Add(@"Box");
            id3_Boxes = Reader.NameTable.Add(@"Boxes");
            id1_X = Reader.NameTable.Add(@"X");
            id2_Item = Reader.NameTable.Add(@"");
            id6_x = Reader.NameTable.Add(@"x");
            id4_ArrayOfBox = Reader.NameTable.Add(@"ArrayOfBox");
        }
    }

    public abstract class XmlSerializer1 : System.Xml.Serialization.XmlSerializer
    {
        protected override System.Xml.Serialization.XmlSerializationReader CreateReader()
        {
            return new XmlSerializationReaderX();
        }
        protected override System.Xml.Serialization.XmlSerializationWriter CreateWriter()
        {
            return new XmlSerializationWriterX();
        }
    }

    public sealed class XSerializer : XmlSerializer1
    {

        public override System.Boolean CanDeserialize(System.Xml.XmlReader xmlReader)
        {
            return xmlReader.IsStartElement(@"X", @"");
        }

        protected override void Serialize(object objectToSerialize, System.Xml.Serialization.XmlSerializationWriter writer)
        {
            ((XmlSerializationWriterX)writer).Write4_X(objectToSerialize);
        }

        protected override object Deserialize(System.Xml.Serialization.XmlSerializationReader reader)
        {
            return ((XmlSerializationReaderX)reader).Read4_X();
        }
    }

    public class XmlSerializerContract : global::System.Xml.Serialization.XmlSerializerImplementation
    {
        public override global::System.Xml.Serialization.XmlSerializationReader Reader { get { return new XmlSerializationReaderX(); } }
        public override global::System.Xml.Serialization.XmlSerializationWriter Writer { get { return new XmlSerializationWriterX(); } }
        System.Collections.Hashtable readMethods = null;
        public override System.Collections.Hashtable ReadMethods
        {
            get
            {
                if (readMethods == null)
                {
                    System.Collections.Hashtable _tmp = new System.Collections.Hashtable();
                    _tmp[@"expirement.X::"] = @"Read4_X";
                    if (readMethods == null) readMethods = _tmp;
                }
                return readMethods;
            }
        }
        System.Collections.Hashtable writeMethods = null;
        public override System.Collections.Hashtable WriteMethods
        {
            get
            {
                if (writeMethods == null)
                {
                    System.Collections.Hashtable _tmp = new System.Collections.Hashtable();
                    _tmp[@"expirement.X::"] = @"Write4_X";
                    if (writeMethods == null) writeMethods = _tmp;
                }
                return writeMethods;
            }
        }
        System.Collections.Hashtable typedSerializers = null;
        public override System.Collections.Hashtable TypedSerializers
        {
            get
            {
                if (typedSerializers == null)
                {
                    System.Collections.Hashtable _tmp = new System.Collections.Hashtable();
                    _tmp.Add(@"expirement.X::", new XSerializer());
                    if (typedSerializers == null) typedSerializers = _tmp;
                }
                return typedSerializers;
            }
        }
        public override System.Boolean CanSerialize(System.Type type)
        {
            if (type == typeof(global::expirement.X)) return true;
            return false;
        }
        public override System.Xml.Serialization.XmlSerializer GetSerializer(System.Type type)
        {
            if (type == typeof(global::expirement.X)) return new XSerializer();
            return null;
        }
    }
}

Answer 2

Try converting the list to an array, before attempting to serialize it:

List<Box>[] MainArr = new List<Box>[1];
MainArr[0] = new List<Box>();
Box Box1 = new Box(1);
MainArr[0].Add(Box1);

var arr = Array.ConvertAll(MainArr, x => x.ToArray());

System.Xml.Serialization.XmlSerializer writer = new System.Xml.Serialization.XmlSerializer(arr.GetType());
System.IO.StreamWriter fileWrite = new System.IO.StreamWriter(@"C:\Users\Giorgos\Desktop\ConsoleApplication1\ArrListBox.xml");
writer.Serialize(fileWrite, arr);
fileWrite.Close();

The above piece of code produces the following xml on my machine:

    <?xml version="1.0" encoding="utf-8"?>
<ArrayOfArrayOfBox xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ArrayOfBox>
    <Box>
      <x>1</x>
    </Box>
  </ArrayOfBox>
</ArrayOfArrayOfBox>

Answer 3

As a note, you should use a using block for your StreamWriter (see my comments in the code below).

Based on the comments to your question, this looks like a bug in .NET. There are a couple of workarounds that I can see:

Option 1) Use List<List<Box> instead of List<Box>[]

Option 2) Override List<T> (or create your own IList<T> implementation) that implements System.Xml.Serialization.IXmlSerializable . I tested the code below in .NET 3.5 and 4.5.

using System;
using System.Collections.Generic;
using System.IO;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;

namespace experiment
{
    public class Box
    {
        public int x;
        public Box(int a)
        {
            x = a;
        }
        public Box()
        {
        }
    }

    public class XmlList<T> : List<T>, IXmlSerializable
    {
        public XmlSchema GetSchema()
        {
            return null;
        }

        public void ReadXml(XmlReader reader)
        {
            reader.MoveToContent();
            reader.ReadStartElement();
            if (reader.IsEmptyElement)
                return;
            var ser = new XmlSerializer(typeof(T));
            var nodeType = reader.MoveToContent();
            if (nodeType == XmlNodeType.None)
                return;
            while (nodeType != XmlNodeType.EndElement)
            {
                var item = (T)ser.Deserialize(reader);
                if (item == null)
                    continue;
                Add(item);
                nodeType = reader.MoveToContent();
            }
            reader.ReadEndElement();
        }

        public void WriteXml(XmlWriter writer)
        {
            var ser = new XmlSerializer(typeof(T));
            foreach (T item in this)
            {
                ser.Serialize(writer, item);
            }
        }
    }

    public class Program
    {
        static void Main(string[] args)
        {
            var MainArr = new XmlList<Box>[]
            {
                new XmlList<Box>
                {
                    new Box(1),
                    new Box(4)
                }
            };
            var writer = new XmlSerializer(MainArr.GetType());

            // Make sure to use a 'using' block to ensure that the stream gets closed, even if there was a serialization error.
            using (var fileWrite = new StreamWriter(@"test.xml"))
            {
                writer.Serialize(fileWrite, MainArr);
            }
        }
    }
}