focus(n) Tk (4.0) focus(n)
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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
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 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
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focus(n) Tk (4.0) focus(n)
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 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 window'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 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 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
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focus(n) Tk (4.0) focus(n)
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.
KEYWORDS
events, focus, keyboard, top-level, window manager
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