focus(3tk)						       Tk Built-In Commands							focus(3tk)

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NAME

       focus - Manage the input focus

SYNOPSIS

       focus
       focus window
       focus option ?arg arg ...?
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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 man-
       ager 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 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 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 application 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 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 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(3tk)