DOCUMENT:Q192003 11-JAN-2001 [vbwin] TITLE :BUG: Phantom MouseMove Events with a Transparent UserControl PRODUCT :Microsoft Visual Basic for Windows PROD/VER:WINDOWS:5.0,6.0 OPER/SYS: KEYWORDS:kbGrpDSVB ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 ------------------------------------------------------------------------------- SYMPTOMS ======== A Visual Basic UserControl, whose BackStyle property is set to Transparent, may erroneously receive MouseMove messages when the mouse is over the control but is not currently moving. CAUSE ===== The problem occurs because a property or method has been called on the control that causes the control to repaint itself. The repaint event results in a change in the window region for the control, which in turn fires the MouseMove event. This behavior does not occur if the UserControl's BackStyle property is set to Opaque. RESOLUTION ========== Setting the BackStyle property to Opaque offers one approach to working around this problem. However, if this property must be set to Transparent, another potential workaround is to use two static variables to monitor the values of the X and Y coordinates sent to the MouseMove event. If these values are the same as the previous MouseMove event, then you can treat this mouse message as a phantom message. STATUS ====== Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. MORE INFORMATION ================ Steps to Reproduce Behavior --------------------------- 1. Create a new Standard EXE project. Form1 is created by default. 2. From the File menu, add an ActiveX Control project. UserControl1 is created by default. 3. Add a Shape control to UserControl1. 4. Paste the following code into UserControl1's code window: Option Explicit Private Sub UserControl_Initialize() UserControl.BackStyle = 0 'Transparent Shape1.BackStyle = 1 'Opaque End Sub Private Sub UserControl_MouseMove(Button As Integer, Shift As _ Integer, X As Single, Y As Single) Debug.Print "UserControl: Mouse Move" End Sub Public Sub Refresh() Shape1.Refresh End Sub 5. Close the UserControl's code and design windows. 6. Add an instance of UserControl1 to Form1. 7. Add a Timer control to Form1 and set its Interval property to 2000. 8. Paste the following code into Form1's code window: Private Sub Timer1_Timer() Debug.Print "Timer: Is mouse moving?" UserControl11.Refresh End Sub 9. Run the project by pressing the F5 key. 10. Move the mouse over the shape and notice the MouseMove messages in the Immediate Window. 11. Position the mouse over the shape control and stop moving it. When the Timer event fires, a Timer message appears in the Immediate Window, followed immediately by another MouseMove message. The mouse does not need to be moving for this mouse message to appear; it is caused by the Refresh method. 12. Stop the program and change the code in the UserControl_MouseMove event to monitor the values of X and Y and only respond to messages whose X or Y values have changed between calls: Private Sub UserControl_MouseMove(Button As Integer, Shift As _ Integer, X As Single, Y As Single) Static mX As Single, mY As Single If mX <> X Or mY <> Y Then Debug.Print "UserControl: Mouse Move" mX = X mY = Y End If End Sub 13. Repeat steps 9 through 11. With the mouse stationary over the shape, you should see the Timer messages in the Immediate Window, but not the phantom mouse messages. Additional query words: kbDSupport kbDSD extra kbVBp kbCtrl kbVBp600bug kbVBp500bug ====================================================================== Keywords : kbGrpDSVB Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600 Version : WINDOWS:5.0,6.0 Issue type : kbbug ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.