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focus(3)	      User Contributed Perl Documentation	      focus(3)

       focus - Manage the input focus






       The focus methods are 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 method focusFollowsMouse may be invoked to create an implicit focus
       model:  it reconfigures Tk so that the focus is set to a window when‐
       ever the mouse enters it.  The methods focusNext and focusPrev imple‐
       ment 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 methods can take any of the following forms:

	   Returns the focus window on the display containing the $widget,  or
	   an empty string if no window in this application has the focus on
	   that display.

	   If the application currently has the input focus on $widget's dis‐
	   play, this command resets the input focus for $widget's display to
	   $widget and returns an empty string.	 If the application doesn't
	   currently have the  input focus on $widget's display, $widget 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 $widget.

	   Sets the focus of $widget's display to $widget, even if the appli‐
	   cation doesn't 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.

	   Returns the name of the most recent window to have the input focus
	   among all the windows in the same top-level as $widget.  If no win‐
	   dow in that top-level has ever had the input focus, or if the most
	   recent focus window has been deleted, then 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

	   focusNext is a utility method used for keyboard traversal, but can
	   be useful in other contexts.	 It sets the focus to the ``next''
	   window after $widget in focus order.	 The focus order is determined
	   by the stacking order of windows and the structure of the window
	   hierarchy.  Among siblings, the focus order is the same as the
	   stacking order, with the lowest window being first.	If a window
	   has children, the window is visited first, followed by its children
	   (recursively), followed by its next sibling.	 Top-level windows
	   other than $widget are skipped, so that focusNext never returns a
	   window in a different top-level from $widget.

	   After computing the next window, focusNext examines the window's
	   -takefocus option to see whether it should be skipped.  If so,
	   focusNext continues on to the next window in the focus order, until
	   it eventually finds a window that will accept the focus or returns
	   back to $widget.

	   focusPrev is similar to focusNext except that it sets the focus to
	   the window just before $widget in the focus order.

	   focusFollowsMouse changes the focus model for the application to an
	   implicit one where the window under the mouse gets the focus.
	   After this procedure is called, whenever the mouse enters a window
	   Tk will automatically give it the input focus.  The focus command
	   may be used to move the focus to a window other than the one under
	   the mouse, but as soon as the mouse moves into a new window the
	   focus will jump to that window.  Note: at present there is no
	   built-in support for returning the application to an explicit focus
	   model;  to do this you'll have to write a script that deletes the
	   bindings created by focusFollowsMouse.

       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.

       Note that for the Canvas widget, the call to focus has to be fully
       qualified. This is because there is already a focus method for the Can‐
       vas widget, which sets the focus on individual canvas tags.


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

perl v5.8.8			  2004-02-28			      focus(3)

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