SCons.git - SCons is an Open Source software construction tool

	Commit message (Expand)	Author	Age	Files	Lines
*	Raise an error if a builder is called multiple times for a given target, unle...	Steven Knight	2002-05-06	1	-2/+4

*	Add tests for AR and ARFLAGS.	Steven Knight	2002-03-02	1	-0/+97

/**************************************************************************** ** ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:LGPL$ ** No Commercial Usage ** This file contains pre-release code and may not be distributed. ** You may use this file in accordance with the terms and conditions ** contained in the either Technology Preview License Agreement or the ** Beta Release License Agreement. ** ** GNU Lesser General Public License Usage ** Alternatively, this file may be used under the terms of the GNU Lesser ** General Public License version 2.1 as published by the Free Software ** Foundation and appearing in the file LICENSE.LGPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU Lesser General Public License version 2.1 requirements ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Nokia gives you certain ** additional rights. These rights are described in the Nokia Qt LGPL ** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this ** package. ** ** GNU General Public License Usage ** Alternatively, this file may be used under the terms of the GNU ** General Public License version 3.0 as published by the Free Software ** Foundation and appearing in the file LICENSE.GPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU General Public License version 3.0 requirements will be ** met: http://www.gnu.org/copyleft/gpl.html. ** ** If you are unsure which license is appropriate for your use, please ** contact the sales department at http://www.qtsoftware.com/contact. ** $QT_END_LICENSE$ ** ****************************************************************************/ /**************************************************************************** ** ** Documentation of focus handling in Qt. ** ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the Qt GUI Toolkit. ** EDITIONS: FREE, PROFESSIONAL, ENTERPRISE ** ****************************************************************************/ /*! \page focus.html \title Keyboard Focus \ingroup architecture \ingroup gui-programming \brief An overview of the keyboard focus management and handling. \keyword keyboard focus Qt's widgets handle keyboard focus in the ways that have become customary in GUIs. The basic issue is that the user's key strokes can be directed at any of several windows on the screen, and any of several widgets inside the intended window. When the user presses a key, they expect it to go to the right place, and the software must try to meet this expectation. The system must determine which application the key stroke is directed at, which window within that application, and which widget within that window. \section1 Focus Motion The customs which have evolved for directing keyboard focus to a particular widget are these: \list 1 \o The user presses \key Tab (or \key Shift+Tab). \o The user clicks a widget. \o The user presses a keyboard shortcut. \o The user uses the mouse wheel. \o The user moves the focus to a window, and the application must determine which widget within the window should get the focus. \endlist Each of these motion mechanisms is different, and different types of widgets receive focus in only some of them. We'll cover each of them in turn. \section2 Tab or Shift+Tab Pressing \key Tab is by far the most common way to move focus using the keyboard. (Sometimes in data-entry applications Enter does the same as \key{Tab}; this can easily be achieved in Qt by implementing an \l{Events and Event Filters}{event filter}.) Pressing \key Tab, in all window systems in common use today, moves the keyboard focus to the next widget in a circular per-window list. \key Tab moves focus along the circular list in one direction, \key Shift+Tab in the other. The order in which \key Tab presses move from widget to widget is called the tab order. You can customize the tab order using QWidget::setTabOrder(). (If you don't, \key Tab generally moves focus in the order of widget construction.) \l{Qt Designer} provides a means of visually changing the tab order. Since pressing \key Tab is so common, most widgets that can have focus should support tab focus. The major exception is widgets that are rarely used, and where there is some keyboard accelerator or error handler that moves the focus. For example, in a data entry dialog, there might be a field that is only necessary in one per cent of all cases. In such a dialog, \key Tab could skip this field, and the dialog could use one of these mechanisms: \list 1 \o If the program can determine whether the field is needed, it can move focus there when the user finishes entry and presses \gui OK, or when the user presses Enter after finishing the other fields. Alternately, include the field in the tab order but disable it. Enable it if it becomes appropriate in view of what the user has set in the other fields. \o The label for the field can include a keyboard shortcut that moves focus to this field. \endlist Another exception to \key Tab support is text-entry widgets that must support the insertion of tabs; almost all text editors fall into this class. Qt treats \key Ctrl+Tab as \key Tab and \key Ctrl+Shift+Tab as \key Shift+Tab, and such widgets can reimplement QWidget::event() and handle Tab before calling QWidget::event() to get normal processing of all other keys. However, since some systems use \key Ctrl+Tab for other purposes, and many users aren't aware of \key Ctrl+Tab anyway, this isn't a complete solution. \section2 The User Clicks a Widget This is perhaps even more common than pressing \key Tab on computers with a mouse or other pointing device. Clicking to move the focus is slightly more powerful than \key Tab. While it moves the focus \e to a widget, for editor widgets it also moves the text cursor (the widget's internal focus) to the spot where the mouse is clicked. Since it is so common and people are used to it, it's a good idea to support it for most widgets. However, there is also an important reason to avoid it: you may not want to remove focus from the widget where it was. For example, in a word processor, when the user clicks the 'B' (bold) tool button, what should happen to the keyboard focus? Should it remain where it was, almost certainly in the editing widget, or should it move to the 'B' button? We advise supporting click-to-focus for widgets that support text entry, and to avoid it for most widgets where a mouse click has a different effect. (For buttons, we also recommend adding a keyboard shortcut: QAbstractButton and its subclasses make this very easy.) In Qt, only the QWidget::setFocusPolicy() function affects click-to-focus. \section2 The User Presses a Keyboard Shortcut It's not unusual for keyboard shortcuts to move the focus. This can happen implicitly by opening modal dialogs, but also explicitly using focus accelerators such as those provided by QLabel::setBuddy(), QGroupBox, and QTabBar. We advise supporting shortcut focus for all widgets that the user may want to jump to. For example, a tab dialog can have keyboard shortcuts for each of its pages, so the user can press e.g. \key Alt+P to step to the \underline{P}rinting page. It is easy to overdo this: there are only a few keys, and it's also important to provide keyboard shortcuts for commands. \key Alt+P is also used for Paste, Play, Print, and Print Here in the \l{Standard Accelerator Keys} list, for example. \section2 The User Rotates the Mouse Wheel On Microsoft Windows, mouse wheel usage is always handled by the widget that has keyboard focus. On Mac OS X and X11, it's handled by the widget that gets other mouse events. The way Qt handles this platform difference is by letting widgets move the keyboard focus when the wheel is used. With the right focus policy on each widget, applications can work idiomatically correctly on Windows, Mac OS X, and X11. \section2 The User Moves the Focus to This Window In this situation the application must determine which widget within the window should receive the focus. This can be simple: If the focus has been in this window before, then the last widget to have focus should regain it. Qt does this automatically. If focus has never been in this window before and you know where focus should start out, call QWidget::setFocus() on the widget which should receive focus before you call QWidget::show() it. If you don't, Qt will pick a suitable widget. */