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'\" RCS: @(#) $Id: focus.n,v 1.1.1.1 2002-01-16 10:25:49 markom Exp $

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.so man.macros

.TH focus n 4.0 Tk "Tk Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

focus \- Manage the input focus

.SH SYNOPSIS

\fBfocus\fR

.sp

\fBfocus \fIwindow\fR

.sp

\fBfocus \fIoption\fR ?\fIarg arg ...\fR?

.BE

.SH DESCRIPTION

.PP

The \fBfocus\fR command is used to manage the Tk input focus.

At any given time, one window on each display is designated as

the \fIfocus window\fR;  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.

.PP

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 \fIexplicit\fR 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.

.PP

The Tcl procedure \fBtk_focusFollowsMouse\fR may be invoked to

create an \fIimplicit\fR focus model:  it reconfigures Tk so that

the focus is set to a window whenever the mouse enters it.

The Tcl procedures \fBtk_focusNext\fR and \fBtk_focusPrev\fR

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.

.PP

The \fBfocus\fR command can take any of the following forms:

.TP

\fBfocus\fR

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 \fB\-displayof\fR

(see below) so that the code will work in applications using multiple

displays.

.TP

\fBfocus \fIwindow\fR

If the application currently has the input focus on \fIwindow\fR's

display, this command resets the input focus for \fIwindow\fR's display

to \fIwindow\fR and returns an empty string.

If the application doesn't currently have the  input focus on

\fIwindow\fR's display, \fIwindow\fR 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 \fIwindow\fR.

If \fIwindow\fR is an empty string then the command does nothing.

.TP

\fBfocus \-displayof\fR \fIwindow\fR

Returns the name of the focus window on the display containing \fIwindow\fR.

If the focus window for \fIwindow\fR's display isn't in this

application, the return value is an empty string.

.TP

\fBfocus \-force \fIwindow\fR

Sets the focus of \fIwindow\fR's display to \fIwindow\fR, 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 \fIwindow\fR is an empty string then the command does nothing.

.TP

\fBfocus \-lastfor\fR \fIwindow\fR

Returns the name of the most recent window to have the input focus

among all the windows in the same top-level as \fIwindow\fR.

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.

.SH "QUIRKS"

.PP

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.

.SH KEYWORDS

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