Question

I’m having a frustrating time with C# message serialization.
I have a class which has a constructor which looks like this:

public ProposalRequestMessage(int imaNumber, int proposalId, bool trainingFlag, string firstSiteAddress,
                                  bool lastSiteFlag, string lastSiteAddress, int reasonCode,
                                  List<LaneSelection> theLaneSelections)
    {
        ImaNumber = imaNumber;
        ProposalId = proposalId;
        TrainingFlag = trainingFlag;
        FirstSiteAddress = firstSiteAddress;
        LastSiteFlag = lastSiteFlag;
        LastSiteAddress = lastSiteAddress;
        ReasonCode = reasonCode;
        laneSelections = new List<LaneSelection>(theLaneSelections);
    }

The lanesSelections member of the class of of type System.Collections.Generic.List, where a LaneSelection looks like this:

public class LaneSelection
{
    public int LaneId { get; set; }
    public SignalAspect AspectCode { get; set; }

    public LaneSelection()
    {
    }
    public LaneSelection(int laneId, SignalAspect aspectCode)
    {
        LaneId = laneId;
        AspectCode = aspectCode;
    }
}  

A SignalAspect is an enumeration.

I send a message containing an instance of this class over an MSMQ as follows:

System.Messaging.MessageQueue queue = new System.Messaging.MessageQueue(queuename);
        queue.Purge();

System.Messaging.Message msg = new System.Messaging.Message(theMessage, new System.Messaging.XmlMessageFormatter());
        queue.Send(msg);

Using some debug tools, I have found that the resulting XML looks a bit like this:

<?xml version="1.0"?>
<IvtmMessage xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">  
<MessageType>ProposalRequest</MessageType>  
<ProposalRequestMessage>    
    <ImaNumber>0</ImaNumber>    
    <ProposalId>2</ProposalId>    
    <TrainingFlag>false</TrainingFlag>    
    <FirstSiteAddress>M25/4690A</FirstSiteAddress>    
    <LastSiteFlag>false</LastSiteFlag>    
    <LastSiteAddress />    
    <ReasonCode>3</ReasonCode>    
    <LaneSelections>      
        <LaneSelection>        
            <LaneId>1</LaneId>        
            <AspectCode>Advisory20</AspectCode>      
        </LaneSelection>    
    </LaneSelections>  
</ProposalRequestMessage>  

I deserialize the message at the other end like so:

Queue = new System.Messaging.MessageQueue(queueName);
Queue.Formatter = new System.Messaging.XmlMessageFormatter(new Type[] { typeof(IvtmMessage) });
Queue.ReceiveCompleted += new System.Messaging.ReceiveCompletedEventHandler(Queue_ReceiveCompleted);
Queue.BeginReceive(new System.TimeSpan(0, 0, 0, 30));
...
System.Messaging.MessageQueue mq = (System.Messaging.MessageQueue)sender;
try
{    
     // End the asynchronous Receive operation.
     System.Messaging.Message m = mq.EndReceive(e.AsyncResult);

     IvtmMessage message = (IvtmMessage)m.Body;
     DecodeMessage(message);
}
catch (System.Messaging.MessageQueueException ex)
{
     string exception = ex.Message;
}
mq.BeginReceive();

return; 

Every member of the class is correctly deserialized except for the laneSelections element which, although it clearly has a value in the XML, evaluates to a null instances in the deserialized message.

In deseparation I tried adding a List to the class, populating it with the values 1-5 on construction. If this serialized correctly then it would show me that the problem is with the LaneSelection class, but if not then the issue would be with serializing a List. The List did not serialize correctly.

Does anyone know what’s going wrong?

Answer 1

two things;

1. There is “laneSelections” in the IvtmMessage declaration but the serialized XML is “LaneSelections” with a capital L. Xml serialization/deserialization is case sensitive and this is caught me out more than once
2. Have you tried adding the following to the LaneSelections property of the IvtmMessage class as in the code below;

Property definition;

 [XmlArray("LaneSelections"), XmlArrayElement("LaneSelection")]
 public List<LaneSelection> LaneSelections { get; set; }

Without the proper Xml attributes on the properties and classes you’re leaving it up to the serializer to interpret how the properties/objects should be translated