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Tk Built-In Commands                                    focus(1T)



_________________________________________________________________

NAME
     focus - Manage the input focus

SYNOPSIS
     focus
     focus window
     focus option ?arg arg ...?
_________________________________________________________________


DESCRIPTION
     The focus command 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
     whenever  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 normally 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 Tcl procedure tk_focusFollowsMouse  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 Tcl procedures tk_focusNext and tk_focusPrev 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 command can take any of the following forms:

     focus
          Returns the path  name  of  the  focus  window  on  the
          display  containing  the application's main window,  or
          an empty string if no window in  this  application  has
          the  focus  on  that  display.   Note:  it is better to



Tk                      Last change: 4.0                        1






Tk Built-In Commands                                    focus(1T)



          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 command resets the input focus
          for window's display to window  and  returns  an  empty
          string.   If the application doesn't currently have the
          input focus on window's display, window will be  remem-
          bered  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 com-
          mand 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 string.

     focus -force window
          Sets the focus of window's display to window,  even  if
          the  application doesn't currently have the input focus
          for the display.  This command  should  be  used  spar-
          ingly,  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  command
          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  con-
     taining  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.



Tk                      Last change: 4.0                        2






Tk Built-In Commands                                    focus(1T)



EXAMPLE
     To make a window that only participates in the focus traver-
     sal  ring when a variable is set, add the following bindings
     to the widgets before and after it in that focus ring:
          button .before -text "Before"
          button .middle -text "Middle"
          button .after  -text "After"
          checkbutton .flag -variable traverseToMiddle -takefocus 0
          pack .flag -side left
          pack .before .middle .after
          bind .before  {
             if {!$traverseToMiddle} {
                focus .after
                break
             }
          }
          bind .after  {
             if {!$traverseToMiddle} {
                focus .before
                break
             }
          }
          focus .before


KEYWORDS
     events, focus, keyboard, top-level, window manager

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     _______________________________________
    |   ATTRIBUTE TYPE   |  ATTRIBUTE VALUE|
    |____________________|__________________|_
    | Availability       |  runtime/tk-8   |
    |____________________|__________________|_
    | Interface Stability|  Uncommitted    |
    |____________________|_________________|

NOTES
     Source for Tk is available on http://opensolaris.org.













Tk                      Last change: 4.0                        3