Style Plugin Example

Files:

• tools/styleplugin/plugin/simplestyle.cpp
• tools/styleplugin/plugin/simplestyle.h
• tools/styleplugin/plugin/simplestyleplugin.cpp
• tools/styleplugin/plugin/simplestyleplugin.h
• tools/styleplugin/stylewindow/stylewindow.cpp
• tools/styleplugin/stylewindow/stylewindow.h
• tools/styleplugin/stylewindow/main.cpp
• tools/styleplugin/styleplugin.pro
• tools/styleplugin/plugin/plugin.pro
• tools/styleplugin/stylewindow/stylewindow.pro

The Style Plugin example shows how to create a plugin that extends Qt with a new GUI look and feel.

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 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 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 SimpleStylePlugin, which provides 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 StyleWindow, in which we display a QPushButton.

The SimpleStyle and 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 SimpleStylePlugin and the main() function. After we have looked at that, we examine the plugin's profile.

 class SimpleStylePlugin : public QStylePlugin
 {
     Q_OBJECT

 public:
     SimpleStylePlugin() {};

     QStringList keys() const;
     QStyle *create(const QString &key);
 };

 QStringList SimpleStylePlugin::keys() const
 {
     return QStringList() << "SimpleStyle";
 }

 QStyle *SimpleStylePlugin::create(const QString &key)
 {
     if (key.toLower() == "simplestyle")
         return new SimpleStyle;
     return 0;
 }

 int main(int argv, char *args[])
 {
     QApplication app(argv, args);
     QApplication::setStyle(QStyleFactory::create("simplestyle"));

     StyleWindow window;
     window.resize(200, 50);
     window.show();

     return app.exec();
 }

 TEMPLATE    = lib
 CONFIG     += plugin
 HEADERS     = simplestyle.h \
               simplestyleplugin.h
 SOURCES     = simplestyle.cpp \
               simplestyleplugin.cpp
 TARGET      = simplestyleplugin