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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  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	 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  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  con‐
	      taining 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  specify the display explicitly using
	      -displayof (see below) so that the code will  work  in  applica‐
	      tions 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  dis‐
	      play  to window and returns an empty string.  If the application
	      does not currently have the input	 focus	on  window's  display,
	      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 command
	      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 is not 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 appli‐
	      cation  does not currently have the input focus for the display.
	      This command 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 command does noth‐
	      ing.

       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 does not  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.

EXAMPLE
       To  make	 a  window  that only participates in the focus traversal 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 <Tab> {
		 if {!$traverseToMiddle} {
		    focus .after
		    break
		 }
	      }
	      bind .after <Shift-Tab> {
		 if {!$traverseToMiddle} {
		    focus .before
		    break
		 }
	      }
	      focus .before

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

Tk				      4.0			      focus(n)
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