Article ID: 246460
Article Last Modified on 2/23/2007
APPLIES TO
- Microsoft Message Queuing 2.0
This article was previously published under Q246460
SYMPTOMS
The IsLastInTransaction property of a Microsoft Message Queuing, also known as MSMQ, MSMQMessage object returns an Integer result rather than a Boolean. IsLastInTransaction returns a 1 if the message is the last in the transaction 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 message is the last in a transaction both "message.IsLastInTransaction" and "Not message.IsLastInTransaction" evaluate true. In the following example code, if the message is the last in a transaction both message boxes appear:
If message.IsLastInTransaction Then
MsgBox "The message was the last message sent in the transaction."
End If
If Not message.IsLastInTransaction Then
MsgBox "The message was not the last message sent in the transaction."
End If
RESOLUTION
There are two possible workarounds for the problem:
Explicitly test the value of the IsLastInTransaction property against 0 and 1. A value of 1 indicates that the message is the last in the transaction, a value of 0 indicates that the message is not the last in the transaction. An example of this test is shown in the following code:
If MSMQMessageObject.IsLastInTransaction = 1 Then MsgBox "The message was the last message sent in the transaction." End If If MSMQMessageObject.IsLastInTransaction = 0 Then MsgBox "The message was not the last message sent in the transaction." End If- Avoid "negative" tests that use the Not operator with the IsLastInTransaction 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 Message Queuing and will remain consistent. Future versions of the 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 IsLastInTransaction property as follows:
MSMQMessage.IsLastInTransaction
Returned Value
1
The message was the last message sent in the transaction.
0
The message was not the last message sent in the transaction.
REFERENCES
MSDN Online Help for the MSMQMessage Object
Visual Basic Programmer's 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
245753 MSMQQueue Object IsOpen Property Returns an Integer
246458 MSMQMessage Object IsFirstInTransaction Property Returns An Integer
Additional query words: MSMQ MSMQMessage IsLastInTransaction
Keywords: kbprb KB246460
