Knowledge Base

Other Event Incorrectly Triggers CALL SETUEVENT/ON UEVENT Trap

Article ID: 46182

Article Last Modified on 11/21/2006

This article was previously published under Q46182

SYMPTOMS

Due to a software problem, you cannot use the UEVENT trapping in conjunction with any other event trapping in the Basic versions listed below. After CALL SETUEVENT is invoked just once, each subsequent non-user-defined event (such as ON TIMER, ON COM, ON KEY, or ON PLAY) also improperly activates the user-defined event (ON UEVENT GOSUB) trap.

STATUS

Microsoft has confirmed this to be a bug in Microsoft QuickBasic versions 4.0b and 4.5, and in Microsoft Basic Compiler versions 6.0 and 6.0b (buglist6.00, buglist6.00b). This problem was corrected in Microsoft Basic Professional Development System (PDS) version 7.0 for MS-DOS and MS OS/2 (fixlist7.00).

MORE INFORMATION

The problem does not apply to QuickBasic versions 4.0 and earlier because they don't support user-defined event trapping (ON UEVENT GOSUB and CALL SETUEVENT).

Example 1

SETUEVENT improperly activates at the same frequency as the ON TIMER event. This behavior continues to occur until the TIMER OFF statement is used. The problem occurs both in a compiled .EXE program and in the QB.EXE environment. SETUEVENT can be called from another language or from the Basic program itself to reproduce the problem.

The following sample code demonstrates the problem in a compiled .EXE program or in the QB.EXE environment:

' Turn the timer and uevent on:
TIMER ON
UEVENT ON

' Set up the handler routines for events:
ON UEVENT GOSUB ueventhandler
ON TIMER(1) GOSUB timerhandler   ' Timer event occurs every 1 second.

'Invoke a user-defined event just once:
CALL setuevent
PRINT "Press any key to end."
WHILE INKEY$ = ""
WEND
END

ueventhandler:

  PRINT "This uevent should only occur once."
  RETURN

timerhandler:

  PRINT "A timer event occurred."
  ' TIMER OFF   'Add this line to work around the problem.
  RETURN

Example 2

A key trapping event also causes this behavior, for example:

ON UEVENT GOSUB UEtrap
ON KEY(1) GOSUB F1trap
UEVENT ON
KEY(1) ON
PRINT "F1 is trapped. Press enter to trigger Uevent"
WHILE INKEY$ <> CHR$(13): WEND    'F1 key will be trapped
CALL SetUevent             'trigger Uevent
PRINT "Pressing F1 now will cause both events to fire"
WHILE INKEY$ <> CHR$(13): WEND    'Pressing F1 now fires both events
END
UEtrap:
  PRINT "UEvent trapped"
  RETURN
F1trap:
  PRINT "F1 trapped"
  RETURN

Microsoft KB Archive/46182

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