source: trunk/doc/src/qt4-accessibility.qdoc@ 109

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41
42/*!
43 \page qt4-accessibility.html
44 \title Cross-Platform Accessibility Support in Qt 4
45 \ingroup accessibility
46
47 \contentspage {What's New in Qt 4}{Home}
48 \previouspage The New Qt Designer
49 \nextpage The Qt 4 Database GUI Layer
50
51 Qt 4 allows developers to write cross-platform applications that
52 are usable by visually impaired users as well as by users with
53 other disabilities. Qt accessibility will make applications
54 accessible to more users and opens the governmental market, where
55 accessibility is often a requirement.
56
57 \section1 General Overview
58
59 The accessibility classes have been extended in
60 various ways since Qt 3. We added new functions and new enum
61 values, and revised the API to make it more consistent with the
62 rest of Qt. We also added two properties to QWidget,
63 \l{QWidget::accessibleName}{accessibleName} and
64 \l{QWidget::accessibleDescription}{accessibleDescription}, that
65 can be set in \e{Qt Designer} to provide basic help texts without
66 having to write any code.
67
68 Qt's accessibility architecture is as follows. Qt offers one
69 generic interface, QAccessibleInterface, that can be used to
70 wrap all widgets and objects (e.g., QPushButton). This single
71 interface provides all the metadata necessary for the assistive
72 technologies. Qt provides implementations of this interface for
73 its built-in widgets as plugins.
74
75 A more detailed overview of the accessibility support in Qt can
76 be found on the \l Accessibility page.
77
78 \section1 Enabling Accessibility Support
79
80 By default, Qt applications are run with accessibility support
81 enabled on Windows and Mac OS X. On Unix/X11 platforms, applications
82 must be launched in an environment with the \c QT_ACCESSIBILITY
83 variable set to 1. For example, this is set in the following way with
84 the bash shell:
85
86 \snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc environment
87
88 Accessibility features are built into Qt by default when the libraries
89 are configured and built.
90
91 \section1 Creating New Accessible Interfaces
92
93 When you develop custom widgets, you can create custom subclasses
94 of QAccessibleInterface and distribute them as plugins (using
95 QAccessiblePlugin) or compile them into the application.
96 Likewise, Qt's predefined accessibility support can be built as
97 plugin (the default) or directly into the Qt library. The main
98 advantage of using plugins is that the accessibility classes are
99 only loaded into memory if they are actually used; they don't
100 slow down the common case where no assistive technology is being
101 used.
102
103 In addition to QAccessibleInterface, Qt includes two convenience
104 classes, QAccessibleObject and QAccessibleWidget, that
105 provide the lowest common denominator of metadata (e.g., widget
106 geometry, window title, basic help text). You can use them as
107 base classes when wrapping your custom QObject or QWidget
108 subclasses.
109
110 Another new feature in Qt 4 is that Qt can now support other
111 backends in addition to the predefined ones. This is done by
112 subclassing QAccessibleBridge.
113
114 \omit
115 \section1 Software Layering
116
117 Qt Application
118 | links to
119 Qt Accessibility Module
120 | Plugin (in-process)
121 Qt ATK Bridge
122 | links to
123 ATK
124 | Plugin (in-process)
125 at-spi
126 | CORBA
127 assistive technologies
128
129 Windows:
130
131 Qt Application
132 | links to
133 Qt Accessibility Module
134 | COM (?)
135 MSAA
136 | ?
137 assistive technologies
138
139 Mac:
140
141 ?
142 \endomit
143
144 \section1 Example Code
145
146 The first example illustrates how to provide accessibility
147 information for a custom widget. We can use QAccessibleWidget as
148 a base class and reimplement various functions:
149
150 \snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 0
151
152 Here's how we would implement the
153 \l{QAccessibleInterface::doAction()}{doAction()} function to call
154 a function named click() on the wrapped MyWidget object when the
155 user invokes the object's default action or "presses" it.
156
157 \snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 1
158
159 To export the widget interface as a plugin, we must subclass
160 QAccessibleFactory:
161
162 \snippet doc/src/snippets/code/doc_src_qt4-accessibility.qdoc 2
163*/
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