Programmieren von Applikationen in VB

Programming DCOM Clients in VB

This section contains the following topics:

Tips and Notes for Programming

Formating Dates and Times

Error Handling in the VB Program

Reference to the Type Library

Basic Structure of the Program

Example Program

Tutorial

Tips and Notes for Programming

Avoid using global instances of proxy objects. Instead, define these objects locally within individual functions. This results in a much better performance on the MTS, since all resources that are no longer required are released immediately.

Thoroughly execute error handling in your program.

Calling method InitKeys does not include an existancy check for a specific instance in the R/3 database. To do this check, call instance-dependent BAPI methods such as CheckExistence or GetDetail for the individual instances.

For transferring parameters to a BAPI or function module, prefer "Named Arguments" to "Position Arguments".

When calling BAPIs with a large number of arguments, use the OLE/COM Object Viewer. Choose View TypeLib to display the parameter definition of the BAPIs. Then cut and paste them into your VB project (which saves some typing effort).

Study the program examples delivered together with the RFC SDK.

When using the connection parameters (Destination, ClientID,…) and calling the methods PutSessionInfo and AdviceRfcGuiSink, you must cast the object reference to a VB object, since, due to a bug on the MTS, marshalling cannot be executed without this prerequisite.

As in VB the data type Date stores the date as well as the time, we recommend that you define special conversion functions for output parameters (ABAP Õ VB) for presenting dates and times.

Formatting Dates and Times

For Input Paramters (VB Õ ABAP)

When using input parameters to transfer times and dates to ABAP, use the VB data type Date. If necessary, the client can use the same variable to transfer date and time parameters to ABAP.

' example

Dim dDateAndTimeFrom As Date

Dim dDateAndTimeTo   As Date

…

    boAppointmentFactory.Create( … , _

                                       dDateAndTimeFrom, _      'ABAP parameter "FROM_DATE"

                                       dDateAndTimeFrom, _      'ABAP parameter "FROM_TIME"

                                       dDateAndTimeTo , _         'ABAP parameter "TO_DATE"

                                       dDateAndTimeTo , _        'ABAP parameter "To_TIME"

                                      .... )

For Output Paramters (ABAP Õ VB)

When using output parameters to return dates and times from ABAP, consider that in VB only one component is initialized: either date or time. The functions below demonstrate how you can separate the parameters into the respective valid components. You can use one of two different versions:

"Traditional" Version:

This version utilizes a conservative implementation using the format function.
The function "AbapDateAndTimeToDate" combines the date (ABAP type D) and the time (ABAP type T) into a variable Date in VB.

' example:

Dim bo            As new SAP.BO

Dim rs            As Recordset

Dim dateFrom   As Date

    bo.GetList rs        ' calling a BAPI method

    ......

    dateFrom = AbapDateAndTimeToDate(rs.Fields("DATE_FROM"), rs.Fields("TIME_FROM"))

    ......

' combine date and time into a VB date

Function AbapDateAndTimeToDate(aDate As Date, aTime As Date) As Date

Dim d As Date

Dim t As Date

    d = Format(aDate, "Short Date")

    t = Format(aTime, "Long Time")

    AbapDateAndTimeToDate = d + t

End Function

The two functions "AbapDateToDate" and "AbapTimeToDate" separately transform the time and date parameters from ABAP into one variable in VB each:

' returns current date in the system-defined short date format

Function AbapDateToDate(aDate As Date) As Date

AbapDateToDate = Format(aDate, "Short Date")

End Function

' returns current time in the system-defined long time format

Function AbapTimeToDate(aTime As Date) As Date

AbapTimeToDate = Format(aTime, "Long Time")

End Function

Optimized Version:

Use the optimized version to improve the performance of the conversion function.
The function "AbapDateAndTimeToDate" combines the date (ABAP type D) and the time (ABAP type T) into a variable of type Date in VB:

Function AbapDateAndTimeToDate(aDate As Date, aTime As Date) As Date

Dim d As Double

Dim t As Double

    d = Fix(aDate)

    t = (aTime - Fix(aTime))

    AbapDateAndTimeToDate = CDate(d + t)

End Function

The implementation of the function "AbapDateToDate" below enforces the conversion of the date from ABAP to a date of type Date in VB:

' sample:

Dim bo           As new SAP.BO

Dim rs           As Recordset

Dim dFrom     As Date

    ......

    bo.GetList rs       'calling a BAPI method

    .....

    dFrom = AbapDateToDate(rs.Fields("DATE_FROM"))

    .....

Function AbapDateToDate(aDate As Date) As Date

Dim d As Double

    d = Fix(aDate)

    AbapDateToDate = CDate(d)

End Function

The implementation of the function "AbapTimeToDate" below enforces the conversion of the time from ABAP to a date of type Date in VB:

' sample:

Dim bo             As new SAP.BO

Dim rs              As Recordset

Dim dTimeFrom As Date

   ......

    bo.GetList rs        'calling a BAPI method

    dFrom = AbapTimeToDate(rs.Fields("TIME_FROM"))

   ......

Function AbapTimeToDate(aTime As Date) As Date

Dim t As Double

    t = (aTime - Fix(aTime))

    AbapTimeToDate = CDate(t)

End Function

Error Handling in the Client Program

For error handling in the client program, it is reasonable to distinguish between three categories of errors:

Errors connected to the RFC connection.
Errors at the remote call of function modules that raise the exceptions defined in ABAP.
Errors at the call of BAPI methods. Usually, BAPIs do not trigger exceptions. To find the errors, you must evaluate the return parameters, which are defined as structures or, very rarely, as tables.

The error information of the first two categories is recorded by the DCOM Connector; you can query it in VB. If these types of errors occur, the value of Err.Number is unequal to zero. Execute a query accordingly and let the system display a description of the error from Err.Description.

Note: In this case, use the statement On error resume next before starting a call.

For errors at a BAPI call, apart from the query above, you can access predefined return parameters. The most commonly used ABAP Dictionary structures for return parameters are:

BAPIRETURN

BAPIRETURN1

BAPIRET2

Example: Structure of BAPIRETURN

Reference to the Type Library

To be able access generated proxy objects in a VB project, you must create a reference to the corresponding Type Library. Choose Project ® References.

The figure below shows the naming convention for the reference you must make to the Type Library:

Basic Structure of the Program

Programming a VB application consists of the following steps:

Creating an instance for the session object.

Establishing the connection to R/3 system.

Creating anonymous business object.

Defining structure and table parameters using method DimAs (only for importing parameters !)

Filling the input parameters with values.

Calling the object methods (BAPIs or remote functions)

Creating the instance for a certain object type from R/3 (if necessary).

Handling errors and checking the return code information

Displaying and using the R/3 data. Using the Data Bound Grid Control to represent the data.

Example Program: Sales.vbp

Prerequisites

Visual Basic development environment installed on the client machine.

DCOM proxies installed in the MTS.

Reference to Microsoft ADO Recordset 1.5 Library or higher.

If the client application does not run on the same machine like MTS, so you have to install the Export Package from MTS to the client. See also Exporting MTS Packages.

Procedure

To execute the example program, proceed as follows:

Choose rfcsdk ® ccsamp ® Sales.VB.

Double-click on the project file Sales.vbp.
The system starts the development environment of Visual Basic and opens the project SalesOrder.

Choose Project ® References to show or create a reference to the generated DCOM proxies.
A list of all available references appears.

If not created, select the reference to the appropriate Type Library and confirm with OK.

Note: For information on the naming convention, see Reference to the Type Library.

Choose Start to start the application.

In the initial screen, choose SAP ® Logon to log on to a system.
The window for entering the logon data appears.

Enter your logon data if they differ from the preset values and confirm with OK.
Show Maintaining Destinations.

In the initial screen, choose SAP ® Place Order.

Enter valid values for the input parameters.
The example program also contains functions for verifying certain entries.

Note: Use the appropriate input data from your system!

Result

The result containing customer-specific data is displayed in a table:

Tutorial