Calling Windows API From Forms.

Question

For example, how can i call the MessageBoxA function from user32.dll whilst working in an Oracle Forms Application.
Thank you.

Answer 1

You shall have to use the WEBUTIL_C_API.Invoke_Int function for this purpose. Please see the following example that Locks the workstation.
-- IMPORTANT
-- Be sure to review the following My Oracle Support Note
-- Doc ID: 285331.1 - "Exception When Calling PASCAL style Function Via WebUTIL_C_API"
declare
  rc pls_integer;
     f_handle WEBUTIL_C_API.FUNCTIONHANDLE;
     args Webutil_c_api.parameterlist;
     winSysDir varchar2(255) := Client_Win_API_ENVIRONMENT.Get_Windows_Directory || '\system32\';
--- IMPORTANT ---
-- WEBUTIL_C_API CURRENTLY ONLY SUPPORTS CALLING C STYLE LIBRARIES, THEREFORE SOME WINDOWS LIBRARIES CANNOT BE CALLED.
-- ADDITIONALLY, IT IS NOT RECOMMENDED THAT YOU ATTEMPT TO CALL FUNCTIONS WHICH REQUIRE ARGS.
-- USE EXTREME CAUTION WHEN CALLING WINDOWS APIS.
-- BE SURE TO THOROUGHLY TEST BEFORE MOVING TO PRODUCTION
-- LOOK CLOSELY AT BOTH STABILITY AND MEMORY USAGE AS SOME CALLS
-- MAY RESULT IN THE APPEARANCE OF A MEMORY LEAK.
-- This call to USER32.DLL will reference the LOCKWORKSTATION function.
-- If the current OS user does not have a password configured, the workstation may not lock.
-- The Windows LockWorkStation function requires no args to be passed in.
-- WebUtil expects something to be passed in. So an empty paramlist will be created.
begin
If webutil_clientinfo.get_operating_system LIKE 'Win%' Then          
     f_handle := WEBUTIL_C_API.register_function(winSysDir||'user32.dll','LockWorkStation');
     args := WEBUTIL_C_API.create_parameter_list;          
If the function succeeds, the return value is nonzero. Because the function executes asynchronously,
a nonzero return value indicates that the operation has been initiated. It does not indicate whether
the workstation has been successfully locked.  If the function fails, the return value is zero.
    http://msdn.microsoft.com/en-us/library/aa376875(v=VS.85).aspx
     rc := WEBUTIL_C_API.Invoke_Int(winSysDir||'user32.dll','LockWorkStation',args);     
End if;
  WEBUTIL_C_API.Destroy_Parameter_List(args);
  WEBUTIL_C_API.Deregister_Function(f_handle);               
  SYNCHRONIZE;
end;