Qt插件系統的概要實例介紹

一、 對於每一種類型的插件，通常至少需要兩個類：
（1.） 一個是插件封裝器類，它實現了插件通用的API函數；
比如QWSMouseHandler，其定義如下：

1. class Q_GUI_EXPORT QWSMouseHandler
2. {
3. public:
4. explicit QWSMouseHandler(const QString &driver = QString(),
5. const QString &device = QString());
6. virtual ~QWSMouseHandler();
9. virtual void clearCalibration() {}
10. virtual void calibrate(const QWSPointerCalibrationData *) {}
11. virtual void getCalibration(QWSPointerCalibrationData *) const {}
14. virtual void resume() = 0;
15. virtual void suspend() = 0;
18. void limitToScreen(QPoint &pt);
19. void mouseChanged(const QPoint& pos, int bstate, int wheel = 0);
20. const QPoint &pos() const { return mousePos; }
23. void setScreen(const QScreen *screen);
26. protected:
27. QPoint &mousePos;
28. QWSMouseHandlerPrivate *d_ptr;
29. }

該類實現了在嵌入式平台上，一個鼠標設備所具有的屬性和方法。

（2.）一個是一個或多個處理器類，每個處理器類都實現了一種用於特殊類型插件的API；
比如QWSLinuxInputMouseHandler，兩者的關系如下：
QWSLinuxInputMouseHandler --> QWSCalibratedMouseHandler --> QWSMouseHandler
通過封裝器類才能訪問這些處理器類。
除此之外往往還會有一個名稱含有"Factory"的類來在程序運行的時候自動創建合適的插件對象。

比如，QMouseDriverFactory，其定義如下：

1. class Q_GUI_EXPORT QMouseDriverFactory
2. {
3. public:
4. static QStringList keys();
5. static QWSMouseHandler *create(const QString&, const QString &);
6. };

create的實現如下：

1. QWSMouseHandler *QMouseDriverFactory::create(const QString& key, const QString &device){
2. QString driver = key.toLower();
3. #if defined(Q_OS_QNX) && !defined(QT_NO_QWS_MOUSE_QNX)
4. if (driver == QLatin1String("qnx") || driver.isEmpty())
5. return new QQnxMouseHandler(key, device);
6. #endif
7. #if defined(Q_OS_INTEGRITY) && !defined(QT_NO_MOUSE_INTEGRITY)
8. if (driver == QLatin1String("integrity") || driver.isEmpty())
9. return new QIntMouseHandler(key, device);
10. #endif
11. #ifndef QT_NO_QWS_MOUSE_LINUXTP
12. if (driver == QLatin1String("linuxtp") || driver.isEmpty())
13. return new QWSLinuxTPMouseHandler(key, device);
14. #endif
15. #ifndef QT_NO_QWS_MOUSE_PC
16. if (driver == QLatin1String("auto")
17. || driver == QLatin1String("intellimouse")
18. || driver == QLatin1String("microsoft")
19. || driver == QLatin1String("mousesystems")
20. || driver == QLatin1String("mouseman")
21. || driver.isEmpty()) {
22. return new QWSPcMouseHandler(key, device);
23. }
24. #endif
25. #ifndef QT_NO_QWS_MOUSE_TSLIB
26. if (driver == QLatin1String("tslib") || driver.isEmpty())
27. return new QWSTslibMouseHandler(key, device);
28. #endif
29. # ifndef QT_NO_QWS_MOUSE_LINUXINPUT
30. if (driver == QLatin1String("linuxinput") || \
31. driver == QLatin1String("usb") || \
32. driver == QLatin1String("linuxis"))
33. return new QWSLinuxInputMouseHandler(device);
34. # endif
35. #ifndef QT_NO_QWS_MOUSE_QVFB
36. if (driver == QLatin1String("qvfbmouse") || driver == QLatin1String("qvfb"))
37. return new QVFbMouseHandler(key, device);
38. #endif
40. #if !defined(Q_OS_WIN32) || defined(QT_MAKEDLL)
41. #ifndef QT_NO_LIBRARY
42. if (QWSMouseHandlerFactoryInterface *factory = qobject_cast<QWSMouseHandlerFactoryInterface*>(loader()->instance(driver)))
43. return factory->create(driver, device); /*注意：這個地方就會創建QMouseDriverPlugin實現的自定義插件類*/
44. #endif
45. #endif
46. return 0;
47. }

注意：QMouseDriverFactory用於探測並且實例化可用的鼠標驅動，Embeded QT for Linux 在server application運行的時候加載合適的鼠標驅動。 Embeded QT for Linux提供幾個內置的類來實現某些鼠標驅動，比如QWSLinuxInputMouseHandler ；另外，也支持使用Qt的插件機制來實現自定義的驅動程序，驅動程序的編寫也要繼承QWSMouseHandler來具體的進行實現。

二、使用QMouseDriverPlugin來創建自定義的鼠標驅動程序

下面的文字來自於Qt的源文檔：

1. /*!
2. \class QMouseDriverPlugin
3. \ingroup plugins
4. \ingroup qws
6. \brief The QMouseDriverPlugin class is an abstract base class for
7. mouse driver plugins in Qt for Embedded Linux.
9. Note that this class is only available in \l{Qt for Embedded Linux}.
11. \l{Qt for Embedded Linux} provides ready-made drivers for several mouse
12. protocols, see the \l{Qt for Embedded Linux Pointer Handling}{pointer
13. handling} documentation for details. Custom mouse drivers can be
14. implemented by subclassing the QWSMouseHandler class and creating
15. a mouse driver plugin.
17. A mouse driver plugin can be created by subclassing
18. QMouseDriverPlugin and reimplementing the pure virtual keys() and
19. create() functions. By exporting the derived class using the
20. Q_EXPORT_PLUGIN2() macro, The default implementation of the
21. QMouseDriverFactory class will automatically detect the plugin and
22. load the driver into the server application at run-time. See \l
23. {How to Create Qt Plugins} for details.
25. \sa QWSMouseHandler, QMouseDriverFactory
26. */
27. /*!
28. \fn QStringList QMouseDriverPlugin::keys() const
30. Implement this function to return the list of valid keys, i.e. the
31. mouse drivers supported by this plugin.
33. \l{Qt for Embedded Linux} provides ready-made drivers for several mouse
34. protocols, see the \l {Qt for Embedded Linux Pointer Handling}{pointer
35. handling} documentation for details.
37. \sa create()
38. */
39. /*!
40. Constructs a mouse driver plugin with the given \a parent.
42. Note that this constructor is invoked automatically by the
43. Q_EXPORT_PLUGIN2() macro, so there is no need for calling it
44. explicitly.
45. */

具體的創建plugin的實例參見：

《How to Create Qt Plugins》

《Qt for Embedded Linux Pointer Handling》