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/****************************************************************************
**
** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
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** use the contact form at http://qt.digia.com/contact-us.
**
** GNU Free Documentation License Usage
** 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. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example tools/styleplugin
\title Style Plugin Example
\ingroup examples-widgets-tools
\brief This example shows how to create a plugin that extends Qt with a new
GUI look and feel.
\image stylepluginexample.png
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
contributes to widget styling by drawing button backgrounds in
red - not a major contribution, but it still makes a new style.
The new style is platform agnostic in the sense that it is not
based on any specific style implementation, but uses QProxyStyle
to merely tweak the looks in the current application style that
defaults to the native system style.
\note 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., fusion).
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 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 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 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 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 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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