focus(n) Tk Built-In Commands focus(n)_________________________________________________________________NAMEfocus - Manage the input focusSYNOPSISfocus
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 desig-
nated 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 applica-
tion 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 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_focus-
Prev 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
Tk 4.0 1
focus(n) Tk Built-In Commands focus(n)
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 doesn't 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 win-
dow's display isn't 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 doesn't currently have the input
focus for the display. This command should be used
sparingly, if at all. In normal usage, an applica-
tion 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
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.
Tk 4.0 2
focus(n) Tk Built-In Commands focus(n)KEYWORDS
events, focus, keyboard, top-level, window manager
Tk 4.0 3