NAME

       Tk::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->focusLastfor
           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 v5.18.1                                       2012-11-12                                         focus(3pm)