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/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example tools/styleplugin
\title Style Plugin Example
This example shows how to create a plugin that extends Qt with a new
GUI look and feel.
\image stylepluginexample.png
On some platforms, the native style will prevent the button
from having a red background. In this case, try to run the example
in another style (e.g., plastique).
A plugin in Qt is a class stored in a shared library that can be
loaded by a QPluginLoader at run-time. When you create plugins in
Qt, they either extend a Qt application or Qt itself. Writing a
plugin that extends Qt itself is achieved by inheriting one of the
plugin \l{Plugin Classes}{base classes}, reimplementing functions
from that class, and adding a macro. In this example we extend Qt
by adding a new GUI look and feel (i.e., making a new QStyle
available). A high-level introduction to plugins is given in the
plugin \l{How to Create Qt Plugins}{overview document}.
Plugins that provide new styles inherit the QStylePlugin base
class. Style plugins are loaded by Qt and made available through
QStyleFactory; we will look at this later. We have implemented \c
SimpleStylePlugin, which provides \c SimpleStyle. The new style
inherits QWindowsStyle and contributes to widget styling by
drawing button backgrounds in red - not a major contribution, but
it still makes a new style. We test the plugin with \c
StyleWindow, in which we display a QPushButton.
The \c SimpleStyle and \c StyleWindow classes do not contain any
plugin specific functionality and their implementations are
trivial; we will therefore leap past them and head on to the \c
SimpleStylePlugin and the \c main() function. After we have looked
at that, we examine the plugin's profile.
\section1 SimpleStylePlugin Class Definition
\c SimpleStylePlugin inherits QStylePlugin and is the plugin
class.
\snippet examples/tools/styleplugin/plugin/simplestyleplugin.h 0
\c keys() returns a list of style names that this plugin can
create, while \c create() takes such a string and returns the
QStyle corresponding to the key. Both functions are pure virtual
functions reimplemented from QStylePlugin. When an application
requests an instance of the \c SimpleStyle style, which this
plugin creates, Qt will create it with this plugin.
\section1 SimpleStylePlugin Class Implementation
Here is the implementation of \c keys():
\snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 0
Since this plugin only supports one style, we return a QStringList
with the class name of that style.
Here is the \c create() function:
\snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 1
Note that the key for style plugins are case insensitive.
The case sensitivity varies from plugin to plugin, so you need to
check this when implementing new plugins.
\section1 The \c main() function
\snippet examples/tools/styleplugin/stylewindow/main.cpp 0
Qt loads the available style plugins when the QApplication object
is initialized. The QStyleFactory class knows about all styles and
produces them with \l{QStyleFactory::}{create()} (it is a
wrapper around all the style plugins).
\section1 The Simple Style Plugin Profile
The \c SimpleStylePlugin lives in its own directory and have
its own profile:
\snippet examples/tools/styleplugin/plugin/plugin.pro 0
In the plugin profile we need to set the lib template as we are
building a shared library instead of an executable. We must also
set the config to plugin. We set the library to be stored in the
styles folder under stylewindow because this is a path in which Qt
will search for style plugins.
\section1 Related articles and examples
In addition to the plugin \l{How to Create Qt Plugins}{overview
document}, we have other examples and articles that concern
plugins.
In the \l{Echo Plugin Example}{echo plugin example} we show how to
implement plugins that extends Qt applications rather than Qt
itself, which is the case with the style plugin of this example.
The \l{Plug & Paint Example}{plug & paint} example shows how to
implement a static plugin as well as being a more involved example
on plugins that extend applications.
*/
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