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+ − /*!+ −
\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.+ −
*/+ −