Article ID: 245753
Article Last Modified on 2/22/2007
APPLIES TO
- Microsoft Message Queue Server 1.0
- Microsoft Message Queuing 2.0
This article was previously published under Q245753
SYMPTOMS
The IsOpen property of a Microsoft Message Queuing MSMQQueue object returns an Integer result rather than a Boolean.
Note Microsoft Message Queuing is also known as MSMQ.
The IsOpen property returns a 1 if the queue is open and a 0 if it is not. This can cause logic errors in a Visual Basic (VB) program if the property is used in the expression portion of an If, While, or similar conditional statement.
When a numeric value is used in a condition statement in VB, 0 is evaluated as false and all non-zero values are evaluated as true. The Not operator in VB inverts the bits of a value when used on a numeric value. The expression "Not 1" produces the result "-2" which is considered a "true" value in a VB condition statement.
Since VB evaluates both "1" and "Not 1" as true statements, if a queue is open both "queue.IsOpen" and "Not queue.IsOpen" will evaluate true. In the following example code, if the queue is open both message boxes appear:
If queue.IsOpen Then
MsgBox "The queue is open"
End If
If Not queue.IsOpen Then
MsgBox "The queue is closed"
End If
RESOLUTION
There are two possible workarounds for the problem:
Explicitly test the value of the IsOpen property against 0 and 1. A value of 1 indicates that the queue is open, a value of 0 indicates that the queue is not open. An example of this test is shown in the following code:
If MSMQQueueObject.IsOpen = 1 Then MsgBox "The queue is open." End If If MSMQQueueObject.IsOpen = 0 Then MsgBox "The queue is closed" End If- Avoid "negative" tests that use the Not operator with the IsOpen property.
STATUS
It is safe to test explicitly for the 1 and 0 values. These values will not be changed in any future version of Microsoft Message Queuing and will remain consistent. Future versions of the Microsoft Message Queuing ActiveX components may add a property that may be evaluated as a true Boolean type for testing this characteristic.
MORE INFORMATION
The MSDN Online help describes the return values for the IsOpen property as follows:
MSMQQueue.IsOpen
Return Values
1
The queue is open.
0
The queue is not open.
REFERENCES
MSDN Online help for the MSMQQueue object type.
Visual Basic Programmers Guide
246218 MSMQMessage Object IsAuthenticated Property Returns an Integer
246222 MSMQQueueInfo Object IsTransactional Property Returns An Integer
246225 MSMQQueueInfo Object IsWorldReadable Property Returns and Integer
246458 MSMQMessage Object IsFirstInTransaction Property Returns An Integer
246460 MSMQMessage Object IsLastInTransaction Property Returns An Integer
Additional query words: MSMQ MSMQQueue IsOpen
Keywords: kbbug kbprb KB245753
