 |
ActiveTcl User Guide |
 |
- NAME
- focus - Manage the input focus
- SYNOPSIS
- focus
- focus window
- focus option ?arg arg ...?
- DESCRIPTION
- focus
- focus
window
- focus -displayof
window
- focus -force
window
- focus -lastfor
window
- QUIRKS
- EXAMPLE
- KEYWORDS
focus - Manage the input focus
focus
focus window
focus option ?arg arg ...?
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 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.
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.
To make a window that only participates in the focus traversal ring
when a variable is set, add the following bindings to the widgets
before and after it in that focus ring:
button .before -text "Before"
button .middle -text "Middle"
button .after -text "After"
checkbutton .flag -variable traverseToMiddle -takefocus 0
pack .flag -side left
pack .before .middle .after
bind .before <Tab> {
if {!$traverseToMiddle} {
focus .after
break
}
}
bind .after <Shift-Tab> {
if {!$traverseToMiddle} {
focus .before
break
}
}
focus .before
events, focus, keyboard, top-level, window manager
Copyright © 1990-1994 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.