Error Handling

When an error occurs in a COM object e.g. a method invocation failed, the control may throw a COM exception and return an error code. When this happens, FlexCOM raises a DataFlex error. This allows you to trap the error using a standard DataFlex error handler, and handle it in an appropriate way or optionally suppress the error.

The following example demonstrates how to write DataFlex code to handle errors in a currency converter COM object (cComEDConverter). The function IsExchangeRateAvailable tests if the passed currency symbol is available by executing ComGetExchangeRate method and trapping any errors raised and returned by the COM method.

Object oEDConverter is a cComEDConverter

    Property Boolean pbErrorFree True

    Procedure Error_Report Integer iErrNum ;

        Integer iErrLine String sErrMsg

        // Internal error handler to suppress error messages and Set

        // an internal flag.

        Set pbErrorFree To False

    End_Procedure

    Function IsExchangeRateAvailable String sCurrencySymbol ;

        Returns Boolean

        // Tests If the exchange rate is available. This works by

        // trapping the returned error code from ComGetExchangeRate.

        Integer hoOldErrorId

        Boolean bErrFree

        Real rExchangeRate

        // Re-rout DataFlex errors to internal Error_Report Procedure.

        Move Error_Object_ID To hoOldErrorId

        Move Self To Error_Object_ID

        // Send ComGetExchangeRate and test for any returned errors.

        Set pbErrorFree To True

        Get ComGetExchangeRate sCurrencySymbol To rExchangeRate

        Get pbErrorFree To bErrFree

        // reset the DataFlex error handler.

        Move hoOldErrorId To Error_Object_ID

        Function_Return bErrFree

    End_Function // IsExchangeRateAvailable

End_Object

Note that the techniques used here are identical to the error handling techniques you would use in any DataFlex code.

See Also

Error_Report

Error_Object_ID

Programming with COM – General Topics