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update(3tcl)


NAME

   update - Process pending events and idle callbacks

SYNOPSIS

   update ?idletasks?
______________________________________________________________________________

DESCRIPTION

   This  command is used to bring the application "up to date" by entering
   the event loop repeatedly until  all  pending  events  (including  idle
   callbacks) have been processed.

   If  the  idletasks  keyword is specified as an argument to the command,
   then no new events or errors are processed;  only  idle  callbacks  are
   invoked.   This  causes  operations that are normally deferred, such as
   display  updates  and  window  layout  calculations,  to  be  performed
   immediately.

   The  update  idletasks  command is useful in scripts where changes have
   been made to the application's state and  you  want  those  changes  to
   appear  on  the display immediately, rather than waiting for the script
   to complete.  Most display updates are performed as idle callbacks,  so
   update idletasks will cause them to run.  However, there are some kinds
   of updates that only happen  in  response  to  events,  such  as  those
   triggered  by  window  size  changes;  these  updates will not occur in
   update idletasks.

   The update command with no options is useful in scripts where  you  are
   performing   a   long-running   computation  but  you  still  want  the
   application to respond to events such as  user  interactions;   if  you
   occasionally  call  update then user input will be processed during the
   next call to update.

EXAMPLE

   Run computations for about a second and then finish:
          set x 1000
          set done 0
          after 1000 set done 1
          while {!$done} {
              # A very silly example!
              set x [expr {log($x) ** 2.8}]

              # Test to see if our time-limit has been hit.  This would
              # also give a chance for serving network sockets and, if
              # the Tk package is loaded, updating a user interface.
              update
          }

SEE ALSO

   after(3tcl), interp(3tcl)

KEYWORDS

   event, flush, handler, idle, update



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