Receiving Messages with Events
The technique illustrated in Receiving a Message to receive message has a significant
drawback. As long as the process is waiting to receive a message, it can do nothing
else. In other words, the message queue holds the process thread hostage. An
alternative is to establish an MSMQEvent object that allows your application
to respond to incoming messages as events that are raised through this object.
The code below shows an example of how to accomplish this. Be aware that there
are actually three parts to this code. The first two lines are in the General
Declaration portion of the form. They are followed by the Form_Load and event
procedures.
Private RequestQ As MSMQQueue
Private WithEvents RequestEvent As MSMQEvent
Private Sub Form_Load()
Dim QI As New MSMQQueueInfo
QI.PathName = "MyServer\QueueName"
Set RequestQ = QI.Open(MQ_RECEIVE_ACCESS, MQ_DENY_NONE)
Set RequestEvent = New MSMQEvent
RequestQ.EnableNotification RequestEvent
End Sub
Sub RequestEvent_Arrived(ByVal Queue as Object, ByVal Cursor As Long)
Dim InQueue As MSMQQueue
Dim msg As MSMQMessage
Set InQueue = Queue
Set msg = InQueue.Receive(ReceiveTimeOut:=0)
If Not msg is Nothing Then
' Process the message
End If
InQueue.EnableNotification RequestEvent
End Sub
In this example, the EnableNotification method is used to associate an MSMQEvent
object with a queue. This causes the Arrived event to be triggered whenever a
message is posted to that queue. You should also notice that the EnableNotification
method was called again at the bottom of the Arrived procedure. That is because
EnableNotification only sets up the event for the next message.