Using message and exception listeners in .NET

A .NET application uses a message listener to receive messages asynchronously, and it uses an exception listener to be notified asynchronously of a problem with a connection.

• To set up a message listener in order to receive messages asynchronously, complete the following steps:
  1. Define a method that matches the signature of the message listener delegate.
     The method that you define can be either a static or an instance method and can be defined in any accessible class. The delegate signature is as follows:

     
     public delegate void MessageListener(IMessage msg); 
     

     and so you could define the method as:

     
     void SomeMethodName(IMessage msg);
     

  2. Instantiate this method as a delegate using something similar to the following example:

     
     MessageListener OnMsgMethod = new MessageListener(SomeMethodName)

  3. Register the delegate with one or more consumers by setting it to the MessageListener property of the consumer:

     
     consumer.MessageListener = OnMsgMethod;

     You can remove the delegate by setting the MessageListener back to null:

     
     consumer.MessageListener = null;

• To set up an exception listener, complete the following steps.
  The exception listener works in much the same way as the message listener, but has a different delegate definition and is assigned to the connection rather then the message consumer. This is the same as for C++.
  1. Define the method.
     The delegate signature is as follows:

     
     public delegate void ExceptionListener(Exception ex);  

     and so the method defined could be:

     
     void SomeMethodName(Exception ex);

  2. Instantiate this method as a delegate using something similar to the following example:

     
     ExceptionListener OnExMethod = new ExceptionListener(SomeMethodName)

  3. Register the delegate with the connection by setting its ExceptionListener property:

     
     connection.ExceptionListener = OnExMethod ;  

     You can remove the delegate by resetting the ExceptionListener to:

     
     null:  connection.ExceptionListener = null;