DOCUMENT:Q262038 26-OCT-2000 [foxpro] TITLE :PRB: COMRETURNERROR Fails if Error Occurs During Server Creation PRODUCT :Microsoft FoxPro PROD/VER:WINDOWS:5.0,5.0a,6.0 OPER/SYS: KEYWORDS:kbCOMt kbvfp500 kbvfp500a kbvfp600 kbGrpDSFox kbDSupport kbCodeSnippet ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 ------------------------------------------------------------------------------- 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 ====================================================================== 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 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2000.