HOWTO: Use COMRETURNERROR() Function in a OLE Server

• Microsoft Visual FoxPro for Windows, version 6.0

SUMMARY

ComReturnError allows Visual FoxPro 6.0 to make reporting errors from the Visual FoxPro OLE Servers easier. This function gives programmers the ability to create more meaningful messages to return to the client, instead of having the client receive a cryptic message that does not make sense.

MORE INFORMATION

The ComReturnError has two parameters, Source and Description. The Source parameter is at which place the error occurs in code. You may use the Program() function or the cMethod parameter in the Error event to populate the Source parameter.

The Description parameter can be anything needed to describe the error. The information that you may want to return to the client is the actual error message and error number from Visual FoxPro and on which line number that error message occurs. The following class is an example of how to use the ComReturnError function:

1. Create a program called Test.prg and add the following code:

   
         DEFINE CLASS sampleclass AS CUSTOM OLEPUBLIC
          NAME = "sampleclass"
   
         *!* Generror accepts one numeric parameter, which is the error number
         *!* of the Visual FoxPro (VFP) error to generate.
         PROCEDURE generror
         PARAMETER errno
         *!* This raises the error.
         ERROR errno
         ENDPROC
   
         *!* When the error is generated, it triggers the Error event, which
         *!* creates a return statment to pass back to the client.
         PROCEDURE ERROR
         LPARAMETERS nError, cMethod, nLine
         returnstr = ALLTRIM(STR(nError)) + ": "+MESSAGE() +"on Line ;
         "+ALLTRIM(STR(nLine))+" In the sample DLL that was created for this ;
         article"
         ComReturnError(cMethod,returnstr)
         ENDPROC
         ENDDEFINE 




2. Create a project and name it MySample. Add the Test.prg file to the project and make sure it is marked as the main file. Save the project and build a COM DLL.



3. Create an object reference to the class, and call the GenError method by issuing the following code in the Command window:

   
         oX = CreateObject('Mysample.sampleclass')
         oX.generror(1) 

   An error dialog box appears with the following message:

   OLE IDispatch error code 120 from generror: 1: File does not exist. On line 3..

REFERENCES

Visual FoxPro 6.0 Help; search on: "ComReturnError"

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

Additional query words: kbvfp600

Keywords :
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbhowto