1
/****************************************************************************
3
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
4
** Contact: Nokia Corporation (qt-info@nokia.com)
6
** This file is part of the documentation of the Qt Toolkit.
8
** $QT_BEGIN_LICENSE:LGPL$
10
** Licensees holding valid Qt Commercial licenses may use this file in
11
** accordance with the Qt Commercial License Agreement provided with the
12
** Software or, alternatively, in accordance with the terms contained in
13
** a written agreement between you and Nokia.
15
** GNU Lesser General Public License Usage
16
** Alternatively, this file may be used under the terms of the GNU Lesser
17
** General Public License version 2.1 as published by the Free Software
18
** Foundation and appearing in the file LICENSE.LGPL included in the
19
** packaging of this file. Please review the following information to
20
** ensure the GNU Lesser General Public License version 2.1 requirements
21
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
23
** In addition, as a special exception, Nokia gives you certain
24
** additional rights. These rights are described in the Nokia Qt LGPL
25
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
28
** GNU General Public License Usage
29
** Alternatively, this file may be used under the terms of the GNU
30
** General Public License version 3.0 as published by the Free Software
31
** Foundation and appearing in the file LICENSE.GPL included in the
32
** packaging of this file. Please review the following information to
33
** ensure the GNU General Public License version 3.0 requirements will be
34
** met: http://www.gnu.org/copyleft/gpl.html.
36
** If you are unsure which license is appropriate for your use, please
37
** contact the sales department at http://www.qtsoftware.com/contact.
40
****************************************************************************/
42
/****************************************************************************
44
** Documentation of focus handling in Qt.
46
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
47
** Contact: Nokia Corporation (qt-info@nokia.com)
49
** This file is part of the Qt GUI Toolkit.
50
** EDITIONS: FREE, PROFESSIONAL, ENTERPRISE
52
****************************************************************************/
58
\ingroup gui-programming
59
\brief An overview of the keyboard focus management and handling.
61
\keyword keyboard focus
63
Qt's widgets handle keyboard focus in the ways that have become
66
The basic issue is that the user's key strokes can be directed at any
67
of several windows on the screen, and any of several widgets inside
68
the intended window. When the user presses a key, they expect it to go
69
to the right place, and the software must try to meet this
70
expectation. The system must determine which application the key stroke
71
is directed at, which window within that application, and which widget
74
\section1 Focus Motion
76
The customs which have evolved for directing keyboard focus to a
77
particular widget are these:
81
\o The user presses \key Tab (or \key Shift+Tab).
82
\o The user clicks a widget.
83
\o The user presses a keyboard shortcut.
84
\o The user uses the mouse wheel.
85
\o The user moves the focus to a window, and the application must
86
determine which widget within the window should get the focus.
89
Each of these motion mechanisms is different, and different types of
90
widgets receive focus in only some of them. We'll cover each of them
93
\section2 Tab or Shift+Tab
95
Pressing \key Tab is by far the most common way to move focus
96
using the keyboard. (Sometimes in data-entry applications Enter
97
does the same as \key{Tab}; this can easily be achieved in Qt by
98
implementing an \l{Events and Event Filters}{event filter}.)
100
Pressing \key Tab, in all window systems in common use today,
101
moves the keyboard focus to the next widget in a circular
102
per-window list. \key Tab moves focus along the circular list in
103
one direction, \key Shift+Tab in the other. The order in which
104
\key Tab presses move from widget to widget is called the tab order.
106
You can customize the tab order using QWidget::setTabOrder(). (If
107
you don't, \key Tab generally moves focus in the order of widget
108
construction.) \l{Qt Designer} provides a means of visually
109
changing the tab order.
111
Since pressing \key Tab is so common, most widgets that can have focus
112
should support tab focus. The major exception is widgets that are
113
rarely used, and where there is some keyboard accelerator or error
114
handler that moves the focus.
116
For example, in a data entry dialog, there might be a field that
117
is only necessary in one per cent of all cases. In such a dialog,
118
\key Tab could skip this field, and the dialog could use one of
123
\o If the program can determine whether the field is needed, it can
124
move focus there when the user finishes entry and presses \gui OK, or when
125
the user presses Enter after finishing the other fields. Alternately,
126
include the field in the tab order but disable it. Enable it if it
127
becomes appropriate in view of what the user has set in the other
130
\o The label for the field can include a keyboard shortcut that moves
135
Another exception to \key Tab support is text-entry widgets that
136
must support the insertion of tabs; almost all text editors fall
137
into this class. Qt treats \key Ctrl+Tab as \key Tab and \key
138
Ctrl+Shift+Tab as \key Shift+Tab, and such widgets can
139
reimplement QWidget::event() and handle Tab before calling
140
QWidget::event() to get normal processing of all other keys.
141
However, since some systems use \key Ctrl+Tab for other purposes,
142
and many users aren't aware of \key Ctrl+Tab anyway, this isn't a
145
\section2 The User Clicks a Widget
147
This is perhaps even more common than pressing \key Tab on
148
computers with a mouse or other pointing device.
150
Clicking to move the focus is slightly more powerful than \key
151
Tab. While it moves the focus \e to a widget, for editor widgets
152
it also moves the text cursor (the widget's internal focus) to
153
the spot where the mouse is clicked.
155
Since it is so common and people are used to it, it's a good idea to
156
support it for most widgets. However, there is also an important
157
reason to avoid it: you may not want to remove focus from the widget
160
For example, in a word processor, when the user clicks the 'B' (bold)
161
tool button, what should happen to the keyboard focus? Should it
162
remain where it was, almost certainly in the editing widget, or should
163
it move to the 'B' button?
165
We advise supporting click-to-focus for widgets that support text
166
entry, and to avoid it for most widgets where a mouse click has a
167
different effect. (For buttons, we also recommend adding a keyboard
168
shortcut: QAbstractButton and its subclasses make this very easy.)
170
In Qt, only the QWidget::setFocusPolicy() function affects
173
\section2 The User Presses a Keyboard Shortcut
175
It's not unusual for keyboard shortcuts to move the focus. This
176
can happen implicitly by opening modal dialogs, but also
177
explicitly using focus accelerators such as those provided by
178
QLabel::setBuddy(), QGroupBox, and QTabBar.
180
We advise supporting shortcut focus for all widgets that the user
181
may want to jump to. For example, a tab dialog can have keyboard
182
shortcuts for each of its pages, so the user can press e.g. \key
183
Alt+P to step to the \underline{P}rinting page. It is easy to
184
overdo this: there are only a few keys, and it's also important
185
to provide keyboard shortcuts for commands. \key Alt+P is also
186
used for Paste, Play, Print, and Print Here in the \l{Standard
187
Accelerator Keys} list, for example.
189
\section2 The User Rotates the Mouse Wheel
191
On Microsoft Windows, mouse wheel usage is always handled by the
192
widget that has keyboard focus. On Mac OS X and X11, it's handled by
193
the widget that gets other mouse events.
195
The way Qt handles this platform difference is by letting widgets move
196
the keyboard focus when the wheel is used. With the right focus policy
197
on each widget, applications can work idiomatically correctly on
198
Windows, Mac OS X, and X11.
200
\section2 The User Moves the Focus to This Window
202
In this situation the application must determine which widget within
203
the window should receive the focus.
205
This can be simple: If the focus has been in this window before,
206
then the last widget to have focus should regain it. Qt does this
209
If focus has never been in this window before and you know where
210
focus should start out, call QWidget::setFocus() on the widget
211
which should receive focus before you call QWidget::show() it. If
212
you don't, Qt will pick a suitable widget.