Evaluating Function Codes in the Program
When you create new menu and toolbar functions, you must assign a unique code to every function. When the user chooses a function, its function code is placed in the system field SY-UCOMM and the screen field OK_CODE.
The SY-UCOMM field always contains the current function code. You do not need to declare this field in your module pool.
OK_CODE
The OK_CODE field stores the function code in your program. It is always the last field in the field list of a screen. You need to assign a name to this field in the Screen Painter. Traditionally, this field is always called "OK_CODE". However, you can call it anything you like. Once you have assigned a name to the OK_CODE field, you need to declare a field with the same name in your module pool.
Example:
If your GUI status contains the function codes 'BACK', 'EXIT', and 'SAVE', for example, you need the following code in your PAI module.
MODULE USER_COMMAND_0100.
CASE OK_CODE.
WHEN 'BACK'.
...
WHEN 'EXIT'.
...
WHEN 'SAVE'.
...
ENDCASE.
ENDMODULE.