How to Disable Close Command in VB Control Menu (System Menu)

- Standard and Professional Editions of Microsoft Visual Basic for

  Windows, versions 2.0 and 3.0

SUMMARY

To modify an item in the Visual Basic Control menu (also known as the System menu), you need to call the API functions GetSystemMenu and ModifyMenu. This article describes how to disable the Close command in the Control menu.

MORE INFORMATION

If you do not want the user to be able to choose the Close command from the Control menu or to be able to double-click the Control-menu box to end the application, you can disable the Close command. GetSystemMenu returns the handle to the Control menu. That handle can be used by ModifyMenu to change the control menu.

The following code example disables (grays out) the Close command in the Visual Basic Control menu.

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

2. Place a command button (Command1) on Form1. Change its Caption property to Disable Close.

3. Place another command button (Command2) on Form1. Change its caption to Exit.

4. Add the following declarations and constants to the general Declarations section of Form1:

      ' Enter each Declare statement as one, single line:
      Declare Function GetSystemMenu Lib "User" (ByVal hWnd%,
         ByVal bRevert%) as Integer
      Declare Function ModifyMenu Lib "User" (ByVal hMenu%, ByVal nPosition%,
         ByVal wFlags%, ByVal wIDNewItem%, ByVal lpNewItem as Any) as Integer
   
      Const MF_BYCOMMAND = &H0
      Const MF_GRAYED = &H1
      Const SC_CLOSE = &HF060
   
      NOTE: Other constants to disable other menu items in the Control
      menu are described in the CONSTANT.TXT file.
   
   

5. Add the following code to the Command1 Click event:

      Sub Command1_Click ()
         ' See the notes at the end of this article for important additional
         ' information about this code.
         nPosition% = SC_CLOSE
         idNewItem%=-10
         s$ = "Close"
         hMenu% = GetSystemMenu(hWnd, 0)
         wFlags% = MF_BYCOMMAND Or MF_GRAYED
         success% = ModifyMenu(hMenu%, nPosition%, wFlags%, idNewItem%, s$)
      End Sub
   
   

6. Add the following code to the Command2 Click event:

      Sub Command2_Click ()
         End
      End Sub
   
   

7. Press the F5 key to run the program.

8. Click the Control-menu box to see that all the menu items are available.

9. Click the Disable Close command button. Then click the Control-menu box. Notice that the Close menu command is unavailable.

Notes on the Use of ModifyMenu() in the Code

The code listed above uses the ModifyMenu() function, but the EnableMenuItem() may be more appropriate in your particular situation.

Here's the syntax for ModifyMenu():

   ModifyMenu(hMenu, SC_CLOSE, MF_BYCOMMAND|MF_GRAYED, SC_CLOSE, "Close")

   EnableMenuItem(hMenu, SC_CLOSE, MF_BYCOMMAND|MF_GRAYED)

To work around this problem in the code listed above, the second to last argument (idNewItem%) is set to -10 (0 would also work):

   ModifyMenu(hMenu, SC_CLOSE, MF_BYCOMMAND|MF_GRAYED, -10, "Close")

However, because of this workaround, another limitation is introduced. The problem is that the ID of the Close menu item is changed to -10. If you want the program to be able to re-enable the Close item, you'll need to use this alternative version:

   ModifyMenu(hMenu, -10, MF_BYCOMMAND|MF_GRAYED, SC_CLOSE, "Close")

Another alternative solution is to use DeleteMenu to remove Close and the separator above it, and use InsertMenu to add the Close and the separator.

REFERENCES

"Microsoft Windows Programmer's Reference Book and Online Resource" (Visual Basic Add-on kit number 1-55615-413-5)