BUG: Z-Order Behavior Different with OLE (.OCX) Controls

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

The z-order behavior of a control which is now an OLE (.OCX) control is different than it was for the equivalent .VBX control in Microsoft Visual Basic 3.0 for Windows. The OLE (.OCX) control does not overlap (appear on top of) a windowed control like the PictureBox control at design time. This change in z-order behavior is especially noticeable when a Visual Basic 3.0 application is imported into Visual Basic 4.0 and the .VBX controls are upgraded to OLE (.OCX) controls. A control which overlapped a windowed control is now underneath that control. Using the "Bring to Front" command on the Edit menu at design time has no effect. Even at run-time most OLE (.OCX) controls are underneath a windowed control. No matter how the control is overlapped at design time, at run-time it is always on top of lightweight controls and usually underneath windowed controls. This is especially confusing when one of these OLE (.OCX) controls is underneath a lightweight control at design time.

CAUSE

Due to a design limitation in most OLE (.OCX) controls, these controls do not have a window handle (hWnd) at design time. This is different than .VBX controls which have a window handle at design time. Both .VBX and OLE (.OCX) controls have window handles at run-time. Thus the z-order behavior of OLE (.OCX) controls is not consistent with the z-order behavior of .VBX controls because the OLE (.OCX) controls act like lightweight (non-windowed) controls at design time and windowed controls at run-time. In addition some controls do not correctly preserve the relative z-order among windowed controls at run-time, either by forcing themselves on top of or underneath the other windowed controls.

WORKAROUND

Explicitly set the z-order of the OLE (.OCX) controls at run-time with the z-order method. There is currently no way to correct this problem at design time.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The following OLE (.OCX) controls act like lightweight (non-windowed) controls at design time in Visual Basic 4.0:

AniPushButton      MAPIMessages      Slider
CommonDialog       MAPISession       SpinButton
CrystalReport      MaskEdBox         SSCheck
DBCombo            MhState           SSCommand
DBGrid             MMControl         SSOption
DBList             MSComm            SSRibbon
Graph              MSRDC             StatusBar
Grid               Outline           TreeView
ImageList          PictureClip
ListView           ProgressBar

      4.0.

      The DBGrid control cannot be placed underneath a windowed control at
      run-time with the z-order method. Use the z-order method of the
      windowed control to place it on top of the DBGrid control instead.

      The 16-bit Graph control places itself on top of windowed controls at
      run-time. Use its z-order method to place it underneath other
      windowed controls.

      The 32-bit MaskEdBox control places itself on top of windowed
      controls (except for the DBGrid control as noted above) at run-time.
      Use its z-order method to place it underneath other windowed
      controls.

      The Toolbar control places itself on top of windowed controls
     (except for the DBGrid control as noted above) at run-time. Use its
      z-order method to place it underneath other windowed controls.

Steps to Reproduce Problem

1. Start Visual Basic or click New Project (ALT, F, N) on the File menu if Visual Basic is already running. Form1 is created by default.

2. Place the following controls on Form1 in the ORDER listed and in the POSITIONS diagrammed below: Command1, Command2, Command3, Command4, Command5, Command6, Label1, Grid1 and Picture1:

           ------------------------------
          | --------  --------  -------- |
          ||Command1||Command3||Command5||
          | --------  --------  -------- |
          | --------  --------  -------- |
          ||Command2||Command4||Command6||
          | --------  --------  -------- |
          |  --------------              |
          | |Label1        |             |
          | |           ---------------  |
          | |          |Picture1       | |
          | |   -------|               | |
          | |  |Grid1  |               | |
          |  --|       |               | |
          |    |        ---------------  |
          |    |                |        |
          |     ----------------         |
           ------------------------------
   
   

3. Place the following code in Form1:

      Private Sub Form_Load()
          Command1.Caption = "Bring to Front - Label1"
          Command2.Caption = "Send to Back - Label1"
          Label1.BorderStyle = 1
          Command3.Caption = "Bring to Front - Grid1"
          Command4.Caption = "Send to Back - Grid1"
          Command5.Caption = "Bring to Front - Picture1"
          Command6.Caption = "Send to Back - Picture1"
      End Sub
   
   

4. Place the following code in Command1:

      Private Sub Command1_Click()
          Label1.ZOrder 0 'Bring to Front
      End Sub
   
   

5. Place the following code in Command2:

      Private Sub Command2_Click()
          Label1.ZOrder 1 'Send to Back
      End Sub
   
   

6. Place the following code in Command3:

      Private Sub Command3_Click()
          Grid1.ZOrder 0 'Bring to Front
      End Sub
   
   

7. Place the following code in Command4:

      Private Sub Command4_Click()
          Grid1.ZOrder 1 'Send to Back
      End Sub
   
   

8. Place the following code in Command5:

      Private Sub Command5_Click()
          Picture1.ZOrder 0 'Bring to Front
      End Sub
   
   

9. Place the following code in Command6:

      Private Sub Command6_Click()
          Picture1.ZOrder 1 'Send to Back
      End Sub
   
   

10. Select the Grid control and choose "Send to Back" from the Edit menu.

        Notice that the Grid control IS underneath the Label control. In
        Visual Basic 3.0, the Grid control remains on top of the Label
        control.
    

11. Select the PictureBox control and on the Edit menu, click "Send to

        Back". Notice that the PictureBox control IS NOT underneath the Grid
        control. In Visual Basic 3.0, the PictureBox control is underneath the
        Grid control.
    

12. Run the application. If you left the Grid control underneath the Label

        control, notice that it IS NOT underneath the Label control now. Click
        the "Send to Back - Grid1" button. Notice that the Grid control IS NOT
        underneath the Label control now either. This is the way Visual Basic
        3.0 behaves.
    

13. Click the "Send to Back - Picture1" button. Notice that the PictureBox

        control IS now underneath the Grid control. This is the way Visual
        Basic 3.0 behaves.
    

REFERENCES

- Microsoft Visual Basic, Version 4.0, "Programmer's Guide", Appendix C

  "Compatibility with Other Versions", "Visual Basic 3.0 for Windows"
  section, "Z-Order in OCX Controls" subsection.

      most OCX controls behave like lightweight controls at run-time,
      ..." should read "In Visual Basic 4.0, however, most OCX controls
      behave like windowed controls at run-time, regardless of the
      z-order setting at design time.".