source: trunk/doc/src/porting/qt4-accessibility.qdoc@ 762

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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
*/