Serialize Strong Typed Collection. "There was an error reflecting type.."

Question

HI,

I have a class that looks like this:

[Serializable]

public class NewsItems : System.Collections.Generic.List<NewsItem>

{

};

Any it works just fine for 99% of my needs... Here is the 1% problem, when I want to write out the contents of my collection to XML, I get the following error (pasted below) anyone know how to remedy this?

System.InvalidOperationException was unhandled
  Message="There was an error reflecting type 'NewsItems'."
  Source="System.Xml"
  StackTrace:
       at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel)
       at System.Xml.Serialization.XmlReflectionImporter.ImportElement(TypeModel model, XmlRootAttribute root, String defaultNamespace)
       at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type, XmlRootAttribute root, String defaultNamespace)
       at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
       at System.Xml.Serialization.XmlSerializer..ctor(Type type)
       at Driver.Form1.button1_Click(Object sender, EventArgs e) in E:\eZamiRSS\Driver\Form1.cs:line 34
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Driver.Program.Main() in E:\eZamiRSS\Driver\Program.cs:line 17
       at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()

Answer 1

Quick sanity check, is the NewsItem Serializable?

 

Answer 2

Yes it is, (see below) unless there is another attrubute I need to add to the methods/fields/properties?

One thing I can say is when passed through web service, the newsitems is serialized just fine...

 

[Serializable]

public class NewsItem

{

String publishDate;

String originURL;

String link;

String comments;

String title;

String description;

String feedID;

String author;

String rawXML;

Dictionary<String, String> otherValues;

[public get/set properties for each field is only other thing in class]

}

Answer 3

What does the innerException say? (if more than 1 the innermost)

Generally that exception includes an inner exception that explains the problem more explicitly

Answer 4

Yes, I only dug down 1 level, and the inner had a inner, which said that the property I have of type Dictionary<String,String> was unserializable!

 

Thanks

Answer 5

Aha...I knew I had seen this somewhere else before. The SOAP/XML Serializer doesn't support Generics, the team will be implementing all of that jazz in WCF. See this thread for more info.

Answer 6

Mike - The Xml Serializer and SOAP Serializer are not the same thing. The SOAP serailizer is really a formatter used for "deep" serialization, and can be used in remoting along with the binary formatter. The Xml Serializer is used to serialize/deserialize parameters passed to web methods. The Xml Serializer can handle generic collections in Framework 2.0, but it is not capable of serializing dictionaries (including generic ones).

Answer 7

I stand corrected. I guess its understandable why dictionaries would be difficult to support in XML.

Answer 8

Starting in .NET 3.0 you can use the DataContractSerializer instead.  The DataContractSerializer supports generics and dictionaries.  You can find a list of the types supports here: http://msdn2.microsoft.com/en-us/library/ms731923.aspx.

 

Daniel Roth

Answer 9

HI All,

I had similar situation when sending the object to MSMQ, but setting up queue formatter as

Queue.Formatter =

 

new BinaryMessageFormatter(); resolved above issue...

hope it helps,

HydPhani

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HydPhani

Answer 10

The problem is with one of the items you added to the dictionary - it is not serializable.

When the dictionary is empty - does serialization work?

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