I have a class Team that holds a generic list:
[DataContract(Name = "TeamDTO", IsReference = true)]
public class Team
{
[DataMember]
private IList<Person> members = new List<Person>();
public Team()
{
Init();
}
private void Init()
{
members = new List<Person>();
}
[System.Runtime.Serialization.OnDeserializing]
protected void OnDeserializing(StreamingContext ctx)
{
Log("OnDeserializing of Team called");
Init();
if (members != null) Log(members.ToString());
}
[System.Runtime.Serialization.OnSerializing]
private void OnSerializing(StreamingContext ctx)
{
Log("OnSerializing of Team called");
if (members != null) Log(members.ToString());
}
[System.Runtime.Serialization.OnDeserialized]
protected void OnDeserialized(StreamingContext ctx)
{
Log("OnDeserialized of Team called");
if (members != null) Log(members.ToString());
}
[System.Runtime.Serialization.OnSerialized]
private void OnSerialized(StreamingContext ctx)
{
Log("OnSerialized of Team called");
Log(members.ToString());
}
When I use this class in a WCF service, I get following log output
OnSerializing of Team called
System.Collections.Generic.List 1[XXX.Person]
OnSerialized of Team called
System.Collections.Generic.List 1[XXX.Person]
OnDeserializing of Team called
System.Collections.Generic.List 1[XXX.Person]
OnDeserialized of Team called
XXX.Person[]
After the deserialization members
is an Array and no longer a generic list although the field type is IList<> (?!)
When I try to send this object back over the WCF service I get the log output
OnSerializing of Team called
XXX.Person[]
After this my unit test crashes with a System.ExecutionEngineException, which means the WCF service is not able to serialize the array. (maybe because it expected a IList<>)
So, my question is: Does anybody know why the type of my IList<> is an array after deserializing and why I can't serialize my Team object any longer after that?
Thanks
For an introduction to data contracts, see Using Data Contracts. When deserializing XML, the serializer uses the XmlReader and XmlWriter classes. It also supports the XmlDictionaryReader and XmlDictionaryWriter classes to enable it to produce optimized XML in some cases, such as when using the WCF binary XML format.
Windows Communication Foundation (WCF) uses the DataContractSerializer as its default serialization engine to convert data into XML and to convert XML back into data.
Serialization is the process of converting an object into a stream of bytes to store the object or transmit it to memory, a database, or a file. Its main purpose is to save the state of an object in order to be able to recreate it when needed. The reverse process is called deserialization.
DataContractSerializer as the Default By default WCF uses the DataContractSerializer class to serialize data types.
You've run into one of the DataContractSerializer
gotchas.
Fix: Change your private member declaration to:
[DataMember]
private List<Person> members = new List<Person>();
OR change the property to:
[DataMember()]
public IList<Person> Feedback {
get { return m_Feedback; }
set {
if ((value != null)) {
m_Feedback = new List<Person>(value);
} else {
m_Feedback = new List<Person>();
}
}
}
And it will work. The Microsoft Connect bug is here
This problem occurs when you deserialize an object with an IList<T>
DataMember and then try to serialize the same instance again.
If you want to see something cool:
using System;
using System.Collections.Generic;
class TestArrayAncestry
{
static void Main(string[] args)
{
int[] values = new[] { 1, 2, 3 };
Console.WriteLine("int[] is IList<int>: {0}", values is IList<int>);
}
}
It will print int[] is IList<int>: True
.
I suspect this is possibly the reason you see it come back as an array after deserialization, but it is quite non-intuitive.
If you call the Add() method on the IList<int>
of the array though, it throws NotSupportedException
.
One of those .NET quirks.
I got this error while transporting an IList read from a database via LINQ. The WCF was hosted in IIS 7 on a Windows Server 2008 x64.
The app pool crashed with no warnings.
[ServiceBehavior]
public class Webservice : IWebservice
{
public IList<object> GetObjects()
{
return Database.Instance.GetObjects();
}
}
Its not exactly the same problem but may have the same cause.
The resolution for was to install MS hotfix KB973110 http://support.microsoft.com/kb/971030/en-us
It sounds like your WCF service reference is creating a proxy class rather than using the existing type. Proxy classes can only use simple arrays and not any .NET specific types like the generic List.
To avoid this proxy class conversion, in the Add Service Reference screen, click the Advanced button, and then make sure "Reuse types in referenced assemblies" is checked. This will ensure that the existing class (with the generic List) is used when serializing and deserializing the object.
Taken straight from my blog. i hope it will be helpful:
I recently ran into an issue where we were consuming a WCF service and using a custom model binder in our ASP.net MVC app. Everything worked fine excerpt when we were serializing our ILists. IList gets serialized to arrays by default. I ended up converting our the arrays back to ILists using Reflection and calling the following method in the custom model binder. Here is how method looks like:
public object ConvertArraysToIList(object returnObj)
{
if (returnObj != null)
{
var allProps = returnObj.GetType().GetProperties().Where(p => p.PropertyType.IsPublic
&& p.PropertyType.IsGenericType
&& p.PropertyType.Name==typeof(IList<>).Name).ToList();
foreach (var prop in allProps)
{
var value = prop.GetValue(returnObj,null);
//set the current property to a new instance of the IList<>
var arr=(System.Array)value;
Type listType=null;
if(arr!=null)
{
listType= arr.GetType().GetElementType();
}
//create an empty list of the specific type
var listInstance = typeof(List<>)
.MakeGenericType(listType)
.GetConstructor(Type.EmptyTypes)
.Invoke(null);
foreach (var currentValue in arr)
{
listInstance.GetType().GetMethod("Add").Invoke(listInstance, new[] { currentValue });
}
prop.SetValue(returnObj, listInstance, null);
}
}
return returnObj;
}
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