I always had an interest in socket programming. I have created several chat applications and complex socket based applications. When I learned about events in Remoting I was so glad, and the first thing that I thought about was creating a chat application. But in the test, I met with some problems.
The first problem was a security exception:
System.Security.SecurityException: Type System.DelegateSerializationHolder
and the types derived from it (such as System.DelegateSerializationHolder)
are not permitted to be deserialized at this security level.
This problem was solved by adding the
typeFilterLevel attribute with
Full value to the
formatter element of both configuration files.
<formatter ref="soap" typeFilterLevel="Full" />
But again, it did not work and an IO exception occurred:
Exception has been thrown by the target of an invocation. --->
System.IO.FileNotFoundException: Could not load file or assembly
'Client, Version=220.127.116.11, Culture=neutral, PublicKeyToken=null'
or one of its dependencies. The system cannot find the file specified.
This exception occurs while the request is deserialized at the server. The server tries to call the event handler whereas the event handler exists in the client assembly. Because the client assembly is not available at the server, the exception is thrown.
An intermediate wrapper class,
MarshalByRefObject will solve this problem. This wrapper class is located in the shared assembly, accessible for both the client and the server; therefore, a delegate can resolve the method's signature. In the client application, we will associate the shared object event with the
WrapperMessageReceivedHandler method of the wrapper class and associate an event handler on the client with the
MessageReceived event of the wrapper class.
Why [OneWay] Attribute
Without defining the remote method as
[OneWay], an exception will occur when the client is unreachable or has been disconnected without disassociating the event handler. By using
[OneWay], no exception will occur on the client, but it will be in the invocation list of the server and, in longtime, will make your server slower to respond.
Instead of using the normal event invocation mechanism, you must invoke each delegate on your own, and if an exception occurs, you must disassociate the delegate from the invocation list of the event. In the end, you can remove the
public delegate void MessageHandler(string message);
public class RemoteClass:MarshalByRefObject
public event MessageHandler MessageReceived;
public override object InitializeLifetimeService()
public void Send(string message)
if (MessageReceived != null)
MessageHandler messageDelegate = null;
Delegate invocationList_ = null;
invocationList_ = MessageReceived.GetInvocationList();
catch (MemberAccessException ex)
if (invocationList_ != null)
foreach (Delegate del in invocationList_)
messageDelegate = (MessageHandler)del;
catch (Exception e)
MessageReceived -= messageDelegate;
private void Form1_Load(object sender, EventArgs e)
remoteClass = (RemoteClass)Activator.GetObject(typeof(RemoteClass),
wrapperClass = new WrapperClass();
remoteClass.MessageReceived += new
wrapperClass.WrapperMessageReceived += new
public event MessageHandler WrapperMessageReceived;
public void WrapperMessageReceivedHandler(string message)
if(WrapperMessageReceived != null)