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Deserializing Generic List<T> From XML Without XmlAttributes

I am trying to deserialize an xml list to a generic List in C#. I do not want to use XmlAttributes as the solution needs to be generic. I must be getting close as I am getting 3 Item objects but they are all populated with default values, ie: null or 0.
This is not a duplicate of how to deserialize an xml node with a value and an attribute using asp.net serialization which uses XmlAttributes and is not an option. This is clearly stated in the question.
There are a number of SO answers out there whicha I have tried and are similar to what I need, including the other list of SO responses in the [Duplicate]. The code below is modified from one of those answers but does not quite work.
<?xml version="1.0" encoding="utf-8"?>
<root>
---snip---
<Items>
<Item ItemId="1" ItemName="TestName1" Number="100" Created=""></Item>
<Item ItemId="2" ItemName="TestName2" Number="200" Created=""></Item>
<Item ItemId="3" ItemName="TestName3" Number="300" Created=""></Item>
</Items>
</root>
========================================================
var sourceData = XDocument.Parse(xml);
public List<T> GetObjectList<T>(string identifier) where T : class, new()
{
if (sourceData != null && !identifier.isNullOrEmpty())
{
var list = sourceData.Descendants(identifier)
.Select(p => DeserializeObject<T>(p.ToString()))
.ToList();
return list;
}
return new List<T>();
}
public static T DeserializeObject<T>(string xml) where T : class, new()
{
if (string.IsNullOrEmpty(xml))
{
return default(T);
}
try
{
using (var stringReader = new StringReader(xml))
{
var serializer = new XmlSerializer(typeof(T));
return (T) serializer.Deserialize(stringReader);
}
}
catch
{
return default(T);
}
}
public class Item
{
public int ItemId { get; set; }
public string ItemName { get; set; }
public int? Number { get; set;}
public DateTime? Created { get; set; }
}
// RESULT
// Item ItemId="0" ItemName="null" Number="null" Created="null"
// Item ItemId="0" ItemName="null" Number="null" Created="null"
// Item ItemId="0" ItemName="null" Number="null" Created="null"

Check out the XmlSerialzer constructor, you can specify attribute overrides there, if you do not want to modify the class -- you'll need some data defining what you serialize at some point; the XmlSerializer was never written to work without these Attributes, or types that are known to be serializable (numbers, strings, ...).
If you want to be generic, you'll have to write your own serializer, which uses reflection to decide what to serialize, how, and in which order, and what to ignore. You can use the XmlSerializer in it when serializing types that have the necessary attributes. Search for tutorials explaining how to implement IXmlSerializable, they will show you how to use XmlWriter / XmlReader to avoid handling the XML syntax yourself.
A guess why it is like this: Circular references make (de-)serialization really hard, and a generic solution would probably try to serialize this without coming to an end, causing weird bugs with the call hanging forever, when some developer changes one of those classes without being able to see (due to no attribute being there) that they have to write the class in a way avoiding serialization problems.

I asked another similar question (A Better XElement to Object Without XMLAttributes in C#) when this one got marked as a duplicate (for a while) and ended up creating a simple custom de-serializer that met my needs. See the answers there for the code if interested.

Is it possible to serialize property attributes to XML attributes in C#?

Background: This question is about logging the change tracking of a POCO class in C# .NET 4.0.
Let's say I have a Person class with a Name (string) property. That Name property has a custom Attribute called [IsDirty(true/false)] that is set dynamically by a property-auditing class.
[IsDirty(true)]
public string Name { get; set; }
After the changes are detected and the attributes are set, I'm storing the object via normal XML Serialization in a MS SQL Database (XML column type).
What I can't figure out is if it's possible to somehow serialize my custom attribute IsDirty along with it's current value - preferably as an XML attribute on the serialized XML element (Name) so that the final xml is like:
<Name IsDirty="true">John</Name>
Any ideas/info would be appreciated-

I think you're going to have to write your own XML serialization for this and mix in some reflection to check attribute values on properties.
There's a good guide to implementing the IXMLSerializable interface here. Unfortunately you will have to implement serialization of all properties in the class, but on the bright side, if you implement IXmlSerializable correctly, you can still use the XmlSerializer class.
In your serialization code, you can check the attribute value using something like this:
public class YourClass : IXmlSerializable
{
[IsDirty(true)]
public string Name { get; set; }
// skipped ReadXml and GetSchema interface methods for brevity
public void WriteXml(XmlWriter writer)
{
writer.WriteStartElement("YourClass");
var myType = typeof(YourClass);
foreach(var propInfo in myType.GetProperties())
{
writer.WriteStartElement(propInfo.Name);
foreach(var attr in propInfo.GetCustomAttributes(typeof(IsDirtyAttribute), false))
{
var myAttr = attr as IsDirtyAttribute;
writer.WriteAttributeString("Dirty", attr.Value ? "true" : "false");
}
writer.WriteEndElement();
}
writer.WriteEndElement();
}
}
This code is untested and written from memory, so there are probably some bugs lurking around, but hopefully it'll get you on the right track.

It would be possible by manually reading your Attribute and its value. You could do this by wrapping the serialization and deserialization in methods that appended/read the to/from the xml and the attribute..
However I would inherit these classes from a base class that had the property IsDirty then you neednt worry!

XMLDeserialize, "There was an error reflecting type" [duplicate]

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?

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.

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.

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.

Most common reasons by me:
- the object being serialized has no parameterless constructor
- the object contains Dictionary
- the object has some public Interface members

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

All the objects in the serialization graph have to be serializable.
Since XMLSerializer is a blackbox, check these links if you want to debug further into the serialization process..
Changing where XmlSerializer Outputs Temporary Assemblies
HOW TO: Debug into a .NET XmlSerializer Generated Assembly

If you need to handle specific attributes (i.e. Dictionary, or any class), you can implement the IXmlSerialiable interface, which will allow you more freedom at the cost of more verbose coding.
public class NetService : IXmlSerializable
{
#region Data
public string Identifier = String.Empty;
public string Name = String.Empty;
public IPAddress Address = IPAddress.None;
public int Port = 7777;
#endregion
#region IXmlSerializable Implementation
public XmlSchema GetSchema() { return (null); }
public void ReadXml(XmlReader reader)
{
// Attributes
Identifier = reader[XML_IDENTIFIER];
if (Int32.TryParse(reader[XML_NETWORK_PORT], out Port) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_PORT);
if (IPAddress.TryParse(reader[XML_NETWORK_ADDR], out Address) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_ADDR);
}
public void WriteXml(XmlWriter writer)
{
// Attributes
writer.WriteAttributeString(XML_IDENTIFIER, Identifier);
writer.WriteAttributeString(XML_NETWORK_ADDR, Address.ToString());
writer.WriteAttributeString(XML_NETWORK_PORT, Port.ToString());
}
private const string XML_IDENTIFIER = "Id";
private const string XML_NETWORK_ADDR = "Address";
private const string XML_NETWORK_PORT = "Port";
#endregion
}
There is an interesting article, which show an elegant way to implements a sophisticated way to "extend" the XmlSerializer.
The article say:
IXmlSerializable is covered in the official documentation, but the documentation states it's not intended for public use and provides no information beyond that. This indicates that the development team wanted to reserve the right to modify, disable, or even completely remove this extensibility hook down the road. However, as long as you're willing to accept this uncertainty and deal with possible changes in the future, there's no reason whatsoever you can't take advantage of it.
Because this, I suggest to implement you're own IXmlSerializable classes, in order to avoid too much complicated implementations.
...it could be straightforward to implements our custom XmlSerializer class using reflection.

I just got the same error and discovered that a property of type IEnumerable<SomeClass> was the problem. It appears that IEnumerable cannot be serialized directly.
Instead, one could use List<SomeClass>.

I've discovered that the Dictionary class in .Net 2.0 is not serializable using XML, but serializes well when binary serialization is used.
I found a work around here.

I recently got this in a web reference partial class when adding a new property. The auto generated class was adding the following attributes.
[System.Xml.Serialization.XmlElementAttribute(Order = XX)]
I needed to add a similar attribute with an order one higher than the last in the auto generated sequence and this fixed it for me.

I too thought that the Serializable attribute had to be on the object but unless I'm being a complete noob (I am in the middle of a late night coding session) the following works from the SnippetCompiler:
using System;
using System.IO;
using System.Xml;
using System.Collections.Generic;
using System.Xml.Serialization;
public class Inner
{
private string _AnotherStringProperty;
public string AnotherStringProperty
{
get { return _AnotherStringProperty; }
set { _AnotherStringProperty = value; }
}
}
public class DataClass
{
private string _StringProperty;
public string StringProperty
{
get { return _StringProperty; }
set{ _StringProperty = value; }
}
private Inner _InnerObject;
public Inner InnerObject
{
get { return _InnerObject; }
set { _InnerObject = value; }
}
}
public class MyClass
{
public static void Main()
{
try
{
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
TextWriter writer = new StreamWriter(#"c:\tmp\dataClass.xml");
DataClass clazz = new DataClass();
Inner inner = new Inner();
inner.AnotherStringProperty = "Foo2";
clazz.InnerObject = inner;
clazz.StringProperty = "foo";
serializer.Serialize(writer, clazz);
}
finally
{
Console.Write("Press any key to continue...");
Console.ReadKey();
}
}
}
I would imagine that the XmlSerializer is using reflection over the public properties.

Sometime, this type of error is because you dont have constructur of class without argument

I had a situation where the Order was the same for two elements in a row
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "SeriousInjuryFlag")]
.... some code ...
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "AccidentFlag")]
When I changed the code to increment the order by one for each new Property in the class, the error went away.

I was getting the same error when I created a property having a datatype - Type. On this, I was getting an error - There was an error reflecting type. I kept checking the 'InnerException' of every exception from the debug dock and got the specific field name (which was Type) in my case. The solution is as follows:
[XmlIgnore]
public Type Type { get; set; }

Also note that you cannot serialize user interface controls and that any object you want to pass onto the clipboard must be serializable otherwise it cannot be passed across to other processes.

I have been using the NetDataSerialiser class to serialise
my domain classes. NetDataContractSerializer Class.
The domain classes are shared between client and server.

I had the same issue and in my case the object had a ReadOnlyCollection. A collection must implement Add method to be serializable.

I have a slightly different solution to all described here so far, so for any future civilisation here's mine!
I had declared a datatype of "time" as the original type was a TimeSpan and subsequently changed to a String:
[System.Xml.Serialization.XmlElementAttribute(DataType="time", Order=3)]
however the actual type was a string
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
by removing the DateType property the Xml can be serialized
[System.Xml.Serialization.XmlElementAttribute(Order=3)]
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}

[System.Xml.Serialization.XmlElementAttribute("strFieldName", Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
Or
[XmlIgnore]
string [] strFielsName {get;set;}

serialize only one property of a class

I have a class which have about 20 members. I need to serialize my the object of this class in a XML. But condition is I need only one member in the XML.
How can I do this.
EDIT : But at some time, I would like to serialize all the members. So I can't use [XMLIgnore] attribute.

Add the following attribute for all the members you don't want to serialize,
[XmlIgnore()]
public Type X
{
get;set;
}

You could explicitly implement the IXmlSerializable interface and control the reading/writing of the fields yourself, based on some external parameter, i.e.
class CustomXml: IXmlSerializable
{
public System.Xml.Schema.XmlSchema GetSchema()
{
//
}
public void ReadXml(System.Xml.XmlReader reader)
{
if (SerializationParameter.FullSerialization)
//deserialize everything
else
//deserialize one field only
}
public void WriteXml(System.Xml.XmlWriter writer)
{
if (SerializationParameter.FullSerialization)
//serialize everything
else
//serialize one field only
}
}
where SerializationParameter.FullSerialization is an example of how you could control what is serialized when.

you can put [XmlIgnore] attribute on all members you do not want to be serialized.

There is two ways to make properties non-serializable in.NET using attributes.
You may set attributes [NonSerialized] or [XmlIgnore]
If you serializing in binary or SOAP you should use [NonSerialized], if you want to serialize just in XML you should use [XmlIgnore].
So in your case the answer is [XmlIgnore]
EDIT:
There is no way to apply attributes to properties dynamically.
Here some info about that here: Can attributes be added dynamically in C#? and here Remove C# attribute of a property dynamically
Also as a workout you may have different copies of your class with different attributes.
OR
Have a copy of your class set all props as serializable but populate only properties you need, this way every thing else will be null/empty and after serialization of that class you should get the XML you need.

mark the other attributes
<NonSerializable()> _
Property someproperty
End Property

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?

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.

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.

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.

Most common reasons by me:
- the object being serialized has no parameterless constructor
- the object contains Dictionary
- the object has some public Interface members

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

All the objects in the serialization graph have to be serializable.
Since XMLSerializer is a blackbox, check these links if you want to debug further into the serialization process..
Changing where XmlSerializer Outputs Temporary Assemblies
HOW TO: Debug into a .NET XmlSerializer Generated Assembly

If you need to handle specific attributes (i.e. Dictionary, or any class), you can implement the IXmlSerialiable interface, which will allow you more freedom at the cost of more verbose coding.
public class NetService : IXmlSerializable
{
#region Data
public string Identifier = String.Empty;
public string Name = String.Empty;
public IPAddress Address = IPAddress.None;
public int Port = 7777;
#endregion
#region IXmlSerializable Implementation
public XmlSchema GetSchema() { return (null); }
public void ReadXml(XmlReader reader)
{
// Attributes
Identifier = reader[XML_IDENTIFIER];
if (Int32.TryParse(reader[XML_NETWORK_PORT], out Port) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_PORT);
if (IPAddress.TryParse(reader[XML_NETWORK_ADDR], out Address) == false)
throw new XmlException("unable to parse the element " + typeof(NetService).Name + " (badly formatted parameter " + XML_NETWORK_ADDR);
}
public void WriteXml(XmlWriter writer)
{
// Attributes
writer.WriteAttributeString(XML_IDENTIFIER, Identifier);
writer.WriteAttributeString(XML_NETWORK_ADDR, Address.ToString());
writer.WriteAttributeString(XML_NETWORK_PORT, Port.ToString());
}
private const string XML_IDENTIFIER = "Id";
private const string XML_NETWORK_ADDR = "Address";
private const string XML_NETWORK_PORT = "Port";
#endregion
}
There is an interesting article, which show an elegant way to implements a sophisticated way to "extend" the XmlSerializer.
The article say:
IXmlSerializable is covered in the official documentation, but the documentation states it's not intended for public use and provides no information beyond that. This indicates that the development team wanted to reserve the right to modify, disable, or even completely remove this extensibility hook down the road. However, as long as you're willing to accept this uncertainty and deal with possible changes in the future, there's no reason whatsoever you can't take advantage of it.
Because this, I suggest to implement you're own IXmlSerializable classes, in order to avoid too much complicated implementations.
...it could be straightforward to implements our custom XmlSerializer class using reflection.

I just got the same error and discovered that a property of type IEnumerable<SomeClass> was the problem. It appears that IEnumerable cannot be serialized directly.
Instead, one could use List<SomeClass>.

I've discovered that the Dictionary class in .Net 2.0 is not serializable using XML, but serializes well when binary serialization is used.
I found a work around here.

I recently got this in a web reference partial class when adding a new property. The auto generated class was adding the following attributes.
[System.Xml.Serialization.XmlElementAttribute(Order = XX)]
I needed to add a similar attribute with an order one higher than the last in the auto generated sequence and this fixed it for me.

I too thought that the Serializable attribute had to be on the object but unless I'm being a complete noob (I am in the middle of a late night coding session) the following works from the SnippetCompiler:
using System;
using System.IO;
using System.Xml;
using System.Collections.Generic;
using System.Xml.Serialization;
public class Inner
{
private string _AnotherStringProperty;
public string AnotherStringProperty
{
get { return _AnotherStringProperty; }
set { _AnotherStringProperty = value; }
}
}
public class DataClass
{
private string _StringProperty;
public string StringProperty
{
get { return _StringProperty; }
set{ _StringProperty = value; }
}
private Inner _InnerObject;
public Inner InnerObject
{
get { return _InnerObject; }
set { _InnerObject = value; }
}
}
public class MyClass
{
public static void Main()
{
try
{
XmlSerializer serializer = new XmlSerializer(typeof(DataClass));
TextWriter writer = new StreamWriter(#"c:\tmp\dataClass.xml");
DataClass clazz = new DataClass();
Inner inner = new Inner();
inner.AnotherStringProperty = "Foo2";
clazz.InnerObject = inner;
clazz.StringProperty = "foo";
serializer.Serialize(writer, clazz);
}
finally
{
Console.Write("Press any key to continue...");
Console.ReadKey();
}
}
}
I would imagine that the XmlSerializer is using reflection over the public properties.

Sometime, this type of error is because you dont have constructur of class without argument

I had a situation where the Order was the same for two elements in a row
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "SeriousInjuryFlag")]
.... some code ...
[System.Xml.Serialization.XmlElementAttribute(IsNullable = true, Order = 0, ElementName = "AccidentFlag")]
When I changed the code to increment the order by one for each new Property in the class, the error went away.

I was getting the same error when I created a property having a datatype - Type. On this, I was getting an error - There was an error reflecting type. I kept checking the 'InnerException' of every exception from the debug dock and got the specific field name (which was Type) in my case. The solution is as follows:
[XmlIgnore]
public Type Type { get; set; }

Also note that you cannot serialize user interface controls and that any object you want to pass onto the clipboard must be serializable otherwise it cannot be passed across to other processes.

I have been using the NetDataSerialiser class to serialise
my domain classes. NetDataContractSerializer Class.
The domain classes are shared between client and server.

I had the same issue and in my case the object had a ReadOnlyCollection. A collection must implement Add method to be serializable.

I have a slightly different solution to all described here so far, so for any future civilisation here's mine!
I had declared a datatype of "time" as the original type was a TimeSpan and subsequently changed to a String:
[System.Xml.Serialization.XmlElementAttribute(DataType="time", Order=3)]
however the actual type was a string
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}
by removing the DateType property the Xml can be serialized
[System.Xml.Serialization.XmlElementAttribute(Order=3)]
public string TimeProperty {
get {
return this.timePropertyField;
}
set {
this.timePropertyField = value;
this.RaisePropertyChanged("TimeProperty");
}
}

[System.Xml.Serialization.XmlElementAttribute("strFieldName", Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
Or
[XmlIgnore]
string [] strFielsName {get;set;}