Error when calling a popup window in the initial screen of an application

Question

Hi,
    I am calling a popup window in the Initial screen to select the variant list.
I am getting an error reference to Null Object reference.
Here is the Error.
Runtime Errors         OBJECTS_OBJREF_NOT_ASSIGNED_NO
Exception              CX_SY_REF_IS_INITIAL
Date and Time          15.06.2007 10:00:16
Short text
Access via 'NULL' object reference not possible.
What happened?
Error in the ABAP Application Program
The current ABAP program "CL_WDR_MESSAGE_AREA===========CP" had to be
terminated because it has
come across a statement that unfortunately cannot be executed.
What can you do?
Note down which actions and inputs caused the error.
To process the problem further, contact you SAP system
administrator.
Using Transaction ST22 for ABAP Dump Analysis, you can look
at and manage termination messages, and you can also
keep them for a long time.
Error analysis
An exception occurred that is explained in detail below.
The exception, which is assigned to class 'CX_SY_REF_IS_INITIAL', was not
caught in
procedure "SUPPLY_VIEW_DATA" "(METHOD)", nor was it propagated by a RAISING
clause.
Since the caller of the procedure could not have anticipated that the
exception would occur, the current program is terminated.
The reason for the exception is:
You attempted to use a 'NULL' object reference (points to 'nothing')
access a component.
An object reference must point to an object (an instance of a class)
before it can be used to access components.
Either the reference was never set or it was set to 'NULL' using the
CLEAR statement.
How to correct the error
Probably the only way to eliminate the error is to correct the program.
If the error occures in a non-modified SAP program, you may be able to
find an interim solution in an SAP Note.
If you have access to SAP Notes, carry out a search with the following
keywords:
"OBJECTS_OBJREF_NOT_ASSIGNED_NO" "CX_SY_REF_IS_INITIAL"
"CL_WDR_MESSAGE_AREA===========CP" or "CL_WDR_MESSAGE_AREA===========CM00Q"
"SUPPLY_VIEW_DATA"
If you cannot solve the problem yourself and want to send an error
notification to SAP, include the following information:
1. The description of the current problem (short dump)
To save the description, choose "System->List->Save->Local File
(Unconverted)".
2. Corresponding system log
Display the system log by calling transaction SM21.
Restrict the time interval to 10 minutes before and five minutes
after the short dump. Then choose "System->List->Save->Local File
(Unconverted)".
3. If the problem occurs in a problem of your own or a modified SAP
program: The source code of the program
In the editor, choose "Utilities->More
Utilities->Upload/Download->Download".
4. Details about the conditions under which the error occurred or which
actions and input led to the error.
The exception must either be prevented, caught within proedure
"SUPPLY_VIEW_DATA" "(METHOD)", or its possible occurrence must be declared in
the
RAISING clause of the procedure.
To prevent the exception, note the following:
Looking for Ur valuable suggestions.
Cheers,
Sam

Answer 1

Hi Sam,
The correct code for creating a popup window will be:
  data lo_window_manager type ref to if_wd_window_manager.
  data lo_api_component  type ref to if_wd_component.
  data lo_window         type ref to if_wd_window.
  lo_api_component  = wd_comp_controller->wd_get_api( ).
  lo_window_manager = lo_api_component->get_window_manager( ).
  lo_window         = lo_window_manager->create_window(
                     window_name            = 'WINDOW_NAME'
*                    title                  =
*                    close_in_any_case      = abap_true
                     message_display_mode   = if_wd_window=>co_msg_display_mode_selected
*                    close_button           = abap_true
                     button_kind            = if_wd_window=>co_buttons_okcancel
                     message_type           = if_wd_window=>co_msg_type_none
                     default_button         = if_wd_window=>co_button_ok
  lo_window->open( ).
Hope this helps.
Regards,
Ram