Q262038: PRB: COMRETURNERROR Fails if Error Occurs During Server Creation
Article: Q262038
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a,6.0
Operating System(s):
Keyword(s): kbCOMt kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet
Last Modified: 26-OCT-2000
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0
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SYMPTOMS
========
When you use Microsoft Visual FoxPro, you may make use of the COMRETURNERROR()
function in your Visual FoxPro Component Object Model (COM) servers. However,
COMRETURNERROR only works from method calls. There is no way that COM can return
an error during object creation. As a result, you do not get a detailed error
message if a problem occurs in the INIT of your object and you are using
COMRETURNERROR only.
CAUSE
=====
This problem exists because there is no way that COM can return an error during
object creation.
RESOLUTION
==========
As a possible workaround for this issue, use an approach similar to the
following when you develop your COM server:
1. Build this program code into an .exe file named GOOD_SERVER:
********* START CODE *****************
DEFINE CLASS SERVER AS CUSTOM OLEPUBLIC
xError = .F.
PROCEDURE INIT
ERROR 21
ERROR 22
ERROR 23
ERROR 24
ENDPROC
PROCEDURE ERROR
LPARAMETERS nError, cMethod, nLine
#DEFINE CRLF CHR(13) + CHR(10)
LOCAL cErrStr, cErrTxtFile
cErrTxtFile = ;
JUSTPATH(SUBSTR(SYS(16),AT(' ',SYS(16),2))) + "\COMERR.TXT"
cErrStr = "Error #: " + TRANS(nError) + CRLF + ;
"Method Name: " + cMethod + CRLF + ;
"On Line: " + TRANS(nLine) + CRLF + ;
"Message: " + MESSAGE() + CRLF + ;
"DateTime: " + TTOC(DATETIME()) + CRLF + CRLF
IF "INIT" $ UPPER(cMethod)
STRTOFILE(cErrStr, cErrTxtFile, .T.)
THIS.xError = cErrStr
ELSE
COMRETURNERROR(cMethod, cErrStr)
ENDIF
ENDPROC
ENDDEFINE
***************** END CODE ******************
2. Call the server by using the following code:
********* START CODE *****************
#DEFINE MB_ICONQUESTION 32 && Warning query
#DEFINE MB_YESNO 4 && Yes and No buttons
#DEFINE IDYES 6 && Yes button pressed
#DEFINE CRLF CHR(13) + CHR(10)
#DEFINE MB_OK 6 && OK button pressed
PUBLIC goMyServer
LOCAL lcComInitError, lnReleaseCom
lcComInitError = ""
lnReleaseCom = 0
goMyServer = CREATEOBJECT("GOOD_SERVER.SERVER")
IF VARTYPE(goMyServer) # "O"
MESSAGEBOX("Create Object Failed!")
RETURN .F.
ENDIF
*!* Text in this property means we had an error (default is logical).
IF VARTYPE(goMyServer.xError) = "C"
lcComInitError = goMyServer.xError
lnReleaseCom = MESSAGEBOX("The following error occurred:" + ;
+ CRLF + CRLF + lcComInitError + CRLF + CRLF + ;
"Additional errors may have occurred. Check COMERR.TXT" + CRLF + ;
"in the directory with the object for details. Release the object?", ;
MB_ICONQUESTION + MB_YESNO, ;
"Error Creating Object - Release It?")
IF lnReleaseCom = IDYES
RELEASE goMyServer
MESSAGEBOX("Object Released",MB_OK,"COM ERROR")
ELSE
MESSAGEBOX("Object Remains",MB_OK,"COM ERROR")
ENDIF
RETURN .F.
ENDIF
*!* If goMyServer.xError is still .F., no INIT error occurred,
*!* so do whatever...
MESSAGEBOX("Object Created Successfully")
RELEASE goMyServer
***************** END CODE ******************
The main issue with this approach is that the error message you get from the
message box is only the LAST error that occurred in the INIT of the object
(error 24). To work around this, the object writes any errors out to a file
named COMERR.TXT that resides in the same directory as the server.
STATUS
======
This behavior is by design.
MORE INFORMATION
================
Steps to Reproduce Behavior
---------------------------
1. Build the following program into an executable file called BAD_SERVER.
2. Call the server from the Visual FoxPro Command window by running the oX =
CREATEOBJECT('BAD_SERVER.SERVER') function.
When you run the CREATEOBJECT() function line, note that you see an error message
such as this:
OLE error code 0x800004002: No such interface supported
********** START CODE *************
DEFINE CLASS SERVER AS CUSTOM OLEPUBLIC
PROCEDURE INIT
*!* Cause an error
ERROR 22
ENDPROC
PROCEDURE ERROR
LPARAMETERS nError, cMethod, nLine
#DEFINE CR CHR(13)
LOCAL cErrStr
cErrStr = "Error #: " + TRANS(nError) + CR + ;
"Method Name: " + cMethod + CR + ;
"On Line: " + TRANS(nLine) + CR + ;
"Message: " + MESSAGE()
COMRETURNERROR(cMethod, cErrStr)
ENDPROC
ENDDEFINE
********** END CODE *************
REFERENCES
==========
For additional information on the COMRETURNERROR() function, click the article
numbers below to view the articles in the Microsoft Knowledge Base:
Q187908 HOWTO: Use COMRETURNERROR() Function in a OLE Server
Q259211 PRB: COMRETURNERROR() Only Works Properly if Error Has Occurred
(c) Microsoft Corporation 2000, All Rights Reserved. Contributions by Trevor
Hancock, Microsoft Corporation.
Additional query words: 24
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Keywords : kbCOMt kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet
Technology : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version : WINDOWS:5.0,5.0a,6.0
Issue type : kbprb
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