


focus(n)               Tk Built-In Commands              focus(n)


NAME
       focus - Manage the input focus

SYNOPSIS
       (focus)

       (focus window)

       (focus option ?arg arg ...?)


DESCRIPTION
       The focus procedure is used to manage the Tk input focus.  At any given
       time, one window on each display is designated  as  the  focus  window;
       any  key  press  or key release events for the display are sent to that
       window.  It is normally up to the window manager to redirect the  focus
       among  the  top-level  windows  of a display.  For example, some window
       managers automatically set the input focus to a top-level window  when-
       ever  the  mouse  enters it;  others redirect the input focus only when
       the user clicks on a window.  Usually the window manager will  set  the
       focus  only  to  top-level windows, leaving it up to the application to
       redirect the focus among the children of the top-level.

       Tk remembers one focus window  for  each  top-level  (the  most  recent
       descendant  of  that  top-level to receive the focus);  when the window
       manager gives the focus to a top-level, Tk automatically  redirects  it
       to the remembered window.  Within a top-level Tk uses an explicit focus
       model by default.  Moving the mouse within a top-level  does  not  nor-
       mally  change  the focus;  the focus changes only when a widget decides
       explicitly to claim the focus (e.g., because of  a  button  click),  or
       when the user types a key such as Tab that moves the focus.

       The  STk  procedure  Tk:focus-follows-mouse may be invoked to create an
       implicit focus model:  it reconfigures Tk so that the focus is set to a
       window  whenever the mouse enters it.  The STk procedures Tk:focus-next
       and  Tk:focus-prev implement a focus order among the windows of a  top-
       level;   they  are  used in the default bindings for Tab and Shift-Tab,
       among other things.

       The focus procedure can take any of the following forms:

       (focus)
              Returns the path name of the focus window on  the  display  con-
              taining  the  application's  main window,  or #f if no window in
              this application has the focus on that display.   Note:   it  is
              better  to  specify the display explicitly using :displayof (see
              below) so that the code will work in applications using multiple
              displays.

       (focus window)
              If  the  application  currently  has the input focus on window's
              display, this procedure resets the input focus for window's dis-
              play  to window and returns an empty string.  If the application
              doesn't currently have the  input  focus  on  window's  display,



STk                            3.1                              1





focus(n)               Tk Built-In Commands              focus(n)


              window  will  be remembered as the focus for its top-level;  the
              next time the focus arrives at the top-level, Tk  will  redirect
              it  to  window.  If window is an empty string then the procedure
              does nothing.

       (focus :displayof window)
              Returns the name of the focus window on the  display  containing
              window.   If the focus window for window's display isn't in this
              application, the return value is an empty list.

       (focus :force window)
              Sets the focus of window's display to window, even if the appli-
              cation  doesn't  currently have the input focus for the display.
              This procedure should be used sparingly, if at all.   In  normal
              usage,  an  application  should  not claim the focus for itself;
              instead, it should wait for the window manager to  give  it  the
              focus.   If  window  is  an empty string then the procedure does
              nothing.

       (focus :lastfor window)
              Returns the name of the most recent window  to  have  the  input
              focus among all the windows in the same top-level as window.  If
              no window in that top-level has ever had the input focus, or  if
              the  most recent focus window has been deleted, then the name of
              the top-level is returned.  The return value is the window  that
              will  receive  the  input focus the next time the window manager
              gives the focus to the top-level.


QUIRKS
       When an internal window receives the input focus, Tk  doesn't  actually
       set  the  X  focus to that window;  as far as X is concerned, the focus
       will stay on the top-level window containing the window with the focus.
       However,  Tk  generates  FocusIn  and  FocusOut events just as if the X
       focus were on the internal window.   This approach gets around a number
       of  problems  that  would occur if the X focus were actually moved; the
       fact that the X focus is on the top-level is invisible unless you use C
       code to query the X server directly.

SEE ALSO
       grab
















STk                            3.1                              2


