Visual Basic Code Example: Navigating Using Cursors

 

Applies To: Windows 10, Windows 7, Windows 8, Windows 8.1, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, Windows Server Technical Preview, Windows Vista

This example provides a private Sub procedure that synchronously peeks at each message in the queue, navigating through the queue using a cursor supplied by Message Queuing.

For information about navigating queues with cursors or lookup identifiers, see Navigating Queues.

To navigate a queue using cursors

1. Declare the objects needed to read the messages in the queue.

Note

When declaring the MSMQMessage object when reading messages, the New keyword cannot be used.

1. Obtain an MSMQQueueInfo object. The following example initializes the MSMQQueueInfo object by setting the MSMQQueueInfo.PathName property using the computer name and queue name provided by the caller.

   Because this procedure sets the PathName property of the MSMQQueueInfo object, Message Queuing must obtain the format name of the queue before opening the queue. The format name of a public queue must be retrieved from the directory service, and the format name of a local private queue can be obtained from information stored on the local computer. However, a remote private queue cannot be opened unless the MSMQQueueInfo.FormatName property is set with a direct format name. This procedure can be modified to receive the format name from the caller or to generate a direct format name. The applicable format name can then be used to set the FormatName property. For more information, see Format Names.

2. Call MSMQQueueInfo.Open to open the queue with receive access. When opening a queue with receive access the application can peek at or retrieve the messages in the queue.

3. Call MSMQQueue.PeekCurrent to initialize the cursor. This call points the cursor to the first message in the queue.

4. Using a loop, peek at each message in the queue.

5. When there are no messages left, call MSMQQueue.Close to release resources used to open queue and exit the Sub procedure.

Code Example

The following code example can be run on all versions of Message Queuing.

Private Sub NavigateWithCursor( _  
                               strComputerName As String, _  
                               strQueueName As String _  
                               )  
  ' Declare Message Queuing objects.  
  Dim qinfo As New MSMQQueueInfo  
  Dim q As MSMQQueue  
  Dim msg As MSMQMessage  
  
  ' Set the path name in the MSMQQueueInfo object.  
  qinfo.PathName = strComputerName & "\" & strQueueName  
  On Error GoTo ErrorHandler  
  
  ' Open the queue with receive access.  
  Set q = qinfo.Open(Access:=MQ_RECEIVE_ACCESS, ShareMode:=MQ_DENY_NONE)  
  
  ' Initialize the cursor.  
  Set msg = q.PeekCurrent(ReceiveTimeout:=1000)  
  
  ' Peek at messages in the queue using the cursor.  
  Do While Not msg Is Nothing  
    MsgBox "A message was found in the queue."  
    Set msg = q.PeekNext(ReceiveTimeout:=1000)  
  Loop  
  
  ' Close the queue.  
  q.Close  
  Exit Sub  
  
ErrorHandler:  
  MsgBox "Error " + Hex(Err.Number) + " returned. " + Chr(13) + _  
         "Description: " + Err.Description  
  If Not q Is Nothing And q.IsOpen2 Then  
    q.Close  
  EndIf  
End Sub