The information in this article applies to:
- Professional and Enterprise Editions of Microsoft Visual Basic for
Windows, 16-bit only, version 4.0
SUMMARY
Displaying a modal dialog in the Terminate event of a class module can
cause a lockup of the server providing the class and any clients. This
happens with the 16-bit version of Visual Basic 4.0 on the Windows 95
operating system and can be demonstrated by the ds.vbp and thingtst.vbp
samples in the oleserv sample directory.
STATUS
Microsoft has confirmed this to be an issue 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.
WORKAROUND
Do not show any modal dialogs in the Terminate event of a class. Showing
any modal dialogs, including message boxes, is not recommended in either
the Initialize or Terminate events of a class module because it can
interfere with the creation and/or termination of objects. Both client and
server are halted until the modal dialog is dismissed.
MORE INFORMATION
Steps to reproduce
- Start two instances of Visual Basic 4.0, 16-bit, on Windows 95. Load the
ds.vbp sample located in the \vb4\samples\oleserv directory and click F5
to start the server application.
- Switch to the other running instance of VB4 16 and load the thingtst.vbp
sample, which is also located in the \vb4\samples\oleserv directory. Say
yes to the Could not create reference dialog box if it appears. The
instance of the thing server running in the IDE has changed the registry
so that it is used instead of any previously compiled instances of
ds.exe. The references need to be changed in the client so this is taken
into account.
- On the Tools menu, choose References to show the References dialog box.
Find the MISSING: Demonstration OLE Server entry and clear it. Close the
dialog by clicking OK. Reopen the References dialog and check the
Demonstration OLE Server entry.
- Run the client application and enter a name for the Form Thing. Click
OK, then click OK again to dismiss the message box shown in the
Initialize event.
- Click the New Form Thing button to set the old object reference to
nothing and create a new instance of the Form Thing class. The Thing
Terminate modal dialog box displays, but no longer responds to the
mouse. The client and server are locked up at this point. The server
can be shut down with the Close Program dialog (CTRL+ALT+DELETE and
End Task).