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

NAME

       focus - Manage the input focus

SYNOPSIS

	  $widget->focus

	  $widget->focusOption

	  $widget->focusNext

	  $widget->focusPrev

	  $widget->focusFollowsMouse

DESCRIPTION

       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
       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 method 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 methods focusNext and 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 methods can take any of the following forms:

       $widget->focusCurrent
	   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.

       $widget->focus
	   If the application currently has the input focus on $widget's display, 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.

       $widget->focusForce
	   Sets the focus of $widget's display to $widget, even if the application 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.

       $widget->focusLast
	   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
	   window 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
	   top-level.

       $widget->focusNext
       $widget->focusPrev
	   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.

       $widget->focusFollowsMouse
	   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.

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.

CAVEATS

       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
       Canvas widget, which sets the focus on individual canvas tags.

	   $canvas->Tk::focus

KEYWORDS

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

perl v5.12.1							    2007-05-05								  focus(3)