PRB: LCK Functions Do Not Work in a Private Data Session (180903)
The information in this article applies to:
- Microsoft Visual FoxPro for Windows 5.0
- Microsoft Visual FoxPro for Windows 5.0a
- Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q180903 SYMPTOMS
An ActiveX control (.ocx) has been written in Visual C++ that also makes
use of the Visual FoxPro Library Construction Kit (LCK) functions. The
control may work properly on forms that use the default DataSession but the
control fails when the form uses a private DataSession.
CAUSE
Library Construction Kit function calls do not occur in the DataSession
context of the form that made the call to the .ocx. There is only one
global context in which the Library Construction Kit function can call into
Visual FoxPro, no matter where the call originated.
RESOLUTION
If a private DataSession is necessary, write the ActiveX control completely
in Visual C++ or Visual Basic and expose properties and methods that can be
accessed by Visual FoxPro.
If it is absolutely necessary to use some of the Visual FoxPro LCK
functions in an .ocx that will access tables in a private DataSession, it
may be possible to get the .ocx to work by making the private DataSession
the active DataSession by using the SET DATASESSION TO <nDataSessionNumber>
command. However, this approach is not recommended. Writing the
functionality into the control with another language is a better solution.
STATUS
This behavior is by design.
MORE INFORMATION
FoxPro and Visual FoxPro have included the Library Construction Kit for
many versions. The Library Construction Kit functions allow developers to
write libraries in C that can be loaded by FoxPro or Visual FoxPro to
extend its functionality by accessing the FoxPro API. Starting with Visual
FoxPro version 5.0, the Developer's Guide has included information to help
developers get a start on creating ActiveX controls to access the Visual
FoxPro API. ActiveX controls can make use of the LCK functions if used
within the global context of Visual FoxPro.
Library Construction Kit functions that access tables that may be open in
private DataSessions, such as _DBRead and the other _DBxxxx functions,
_Load, _FindMemo and _FindVar, are some of the functions to avoid in
ActiveX controls that need to work in private DataSessions. However,
depending on what the ActiveX control does and how it does it, other LCK
functions may also fail in private DataSessions. A good test is to try the
control in the default DataSession. If it works there and not a private
DataSession, this article probably applies.
REFERENCES
Microsoft Visual FoxPro "Developer's Guide," version 5.0, pages 645-647.
Examples.dbf located in the \API\Samples folder of Visual FoxPro.
Microsoft Visual FoxPro Help: Library Construction Kit.
| Modification Type: | Major | Last Reviewed: | 12/11/1999 |
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| Keywords: | kbprb KB180903 |
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