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/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
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** this package.
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** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
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**
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****************************************************************************/
/*!
\page qt4-accessibility.html
\title Cross-Platform Accessibility Support in Qt 4
\contentspage {What's New in Qt 4}{Home}
\previouspage The New Qt Designer
\nextpage The Qt 4 Database GUI Layer
Qt 4 allows developers to write cross-platform applications that
are usable by visually impaired users as well as by users with
other disabilities. Qt accessibility will make applications
accessible to more users and opens the governmental market, where
accessibility is often a requirement.
\section1 General Overview
The accessibility classes have been extended in
various ways since Qt 3. We added new functions and new enum
values, and revised the API to make it more consistent with the
rest of Qt. We also added two properties to QWidget,
\l{QWidget::accessibleName}{accessibleName} and
\l{QWidget::accessibleDescription}{accessibleDescription}, that
can be set in \e{Qt Designer} to provide basic help texts without
having to write any code.
Qt's accessibility architecture is as follows. Qt offers one
generic interface, QAccessibleInterface, that can be used to
wrap all widgets and objects (e.g., QPushButton). This single
interface provides all the metadata necessary for the assistive
technologies. Qt provides implementations of this interface for
its built-in widgets as plugins.
A more detailed overview of the accessibility support in Qt can
be found on the \l Accessibility page.
\section1 Enabling Accessibility Support
By default, Qt applications are run with accessibility support
enabled on Windows and Mac OS X. On Unix/X11 platforms, applications
must be launched in an environment with the \c QT_ACCESSIBILITY
variable set to 1. For example, this is set in the following way with
the bash shell:
\snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc environment
Accessibility features are built into Qt by default when the libraries
are configured and built.
\section1 Creating New Accessible Interfaces
When you develop custom widgets, you can create custom subclasses
of QAccessibleInterface and distribute them as plugins (using
QAccessiblePlugin) or compile them into the application.
Likewise, Qt's predefined accessibility support can be built as
plugin (the default) or directly into the Qt library. The main
advantage of using plugins is that the accessibility classes are
only loaded into memory if they are actually used; they don't
slow down the common case where no assistive technology is being
used.
In addition to QAccessibleInterface, Qt includes two convenience
classes, QAccessibleObject and QAccessibleWidget, that
provide the lowest common denominator of metadata (e.g., widget
geometry, window title, basic help text). You can use them as
base classes when wrapping your custom QObject or QWidget
subclasses.
Another new feature in Qt 4 is that Qt can now support other
backends in addition to the predefined ones. This is done by
subclassing QAccessibleBridge.
\omit
\section1 Software Layering
Qt Application
| links to
Qt Accessibility Module
| Plugin (in-process)
Qt ATK Bridge
| links to
ATK
| Plugin (in-process)
at-spi
| CORBA
assistive technologies
Windows:
Qt Application
| links to
Qt Accessibility Module
| COM (?)
MSAA
| ?
assistive technologies
Mac:
?
\endomit
\section1 Example Code
The first example illustrates how to provide accessibility
information for a custom widget. We can use QAccessibleWidget as
a base class and reimplement various functions:
\snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 0
Here's how we would implement the
\l{QAccessibleInterface::doAction()}{doAction()} function to call
a function named click() on the wrapped MyWidget object when the
user invokes the object's default action or "presses" it.
\snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 1
To export the widget interface as a plugin, we must subclass
QAccessibleFactory:
\snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 2
*/
|
