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Q187909: HOWTO: How to Prevent UI in an Out of Process Server

Article: Q187909
Product(s): Microsoft FoxPro
Version(s): WINDOWS:2.5,6.0
Operating System(s): 
Keyword(s): kbvfp600 kbMDAC250
Last Modified: 22-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 6.0 
- Microsoft Data Access Components version 2.5 
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SUMMARY
=======

In an Out of Process Automation Server, it is possible to display a modal dialog
box, Messagebox, error message or Wait Window. However, if you distribute the
server remotely, you do not want to have any user interface display. To prevent
a server from going into a modal state, issue the SYS(2335,0) function.

MORE INFORMATION
================

If any type of modal dialog appears in a remote server, the server processing
stops and the client appears to hang until some type of user interaction handles
the dialog. To prevent the server from going into a modal state, use the
SYS(2335,0) function early in the code. This is the "Unattended Server Mode" and
it causes Visual FoxPro to generate an error if any type of modal user interface
(UI) is attempted in the server code. The error code is 2031:"User-interface
operation not allowed at this time", which is a trappable error.

The following code is a sample of how the SYS(2335,0) prevents any UI from
displaying in an out of process server.

Sample Code
-----------

     DEFINE CLASS sampclass AS custom OLEPUBLIC

        Name = "sampclass"

        Procedure Init
           *!* Turn on unattended mode as early as possible.
           SYS(2335,0)
        ENDPROC

        PROCEDURE GenDisp
           *!* Display some type of UI, this could be anything from an error
           *!* message to a dialog box caused by an ODBC Logon.
           WAIT WINDOW "test"
        ENDPROC

        PROCEDURE Error
           LPARAMETERS nError, cMethod, nLine
           *!* Trap error and return the error message to client.
           returnstr = ALLTRIM(STR(nError)) + ': "'+MESSAGE()+'" on Line ' ;
                       +ALLTRIM(STR(nline))
           ComReturnError(cMethod,returnstr)
        ENDPROC

     ENDDEFINE

To build this code, create a project and name it MySample. Copy and paste this
code into a .prg file and add it to the project. Build the project as an EXE. To
run the sample code from the Command window, issue the following:

     oX = Createobject("MySample.sampclass")
     oX.GenDisp()

A Dialog box should display stating the 2031 error number, message, and line
number where the error occurs.

The SYS(2335) function is only for Out of Process Servers (EXE's); the In Process
servers (DLL's) are by default in unattended mode and can not display any UI.

REFERENCES
==========

Visual FoxPro Help; search on: "SYS(2335)"; topic: "SYS(2335)- Unattended Mode"

(c) Microsoft Corporation 1998, All Rights Reserved.
Contributions by David Botzenhart, Microsoft Corporation


Additional query words: kbvfp600

======================================================================
Keywords          : kbvfp600 kbMDAC250 
Technology        : kbVFPsearch kbAudDeveloper kbMDACSearch kbMDAC250 kbVFP600
Version           : WINDOWS:2.5,6.0
Issue type        : kbhowto

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