plugin.cpp Example File

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  #include <QtQml/QQmlExtensionPlugin>
  #include <QtQml/qqml.h>
  #include <qdebug.h>
  #include <qdatetime.h>
  #include <qbasictimer.h>
  #include <qcoreapplication.h>

  // Implements a "TimeModel" class with hour and minute properties
  // that change on-the-minute yet efficiently sleep the rest
  // of the time.

  class MinuteTimer : public QObject
  {
      Q_OBJECT
  public:
      MinuteTimer(QObject *parent) : QObject(parent)
      {
      }

      void start()
      {
          if (!timer.isActive()) {
              time = QTime::currentTime();
              timer.start(60000-time.second()*1000, this);
          }
      }

      void stop()
      {
          timer.stop();
      }

      int hour() const { return time.hour(); }
      int minute() const { return time.minute(); }

  signals:
      void timeChanged();

  protected:
      void timerEvent(QTimerEvent *)
      {
          QTime now = QTime::currentTime();
          if (now.second() == 59 && now.minute() == time.minute() && now.hour() == time.hour()) {
              // just missed time tick over, force it, wait extra 0.5 seconds
              time.addSecs(60);
              timer.start(60500, this);
          } else {
              time = now;
              timer.start(60000-time.second()*1000, this);
          }
          emit timeChanged();
      }

  private:
      QTime time;
      QBasicTimer timer;
  };

  class TimeModel : public QObject
  {
      Q_OBJECT
      Q_PROPERTY(int hour READ hour NOTIFY timeChanged)
      Q_PROPERTY(int minute READ minute NOTIFY timeChanged)

  public:
      TimeModel(QObject *parent=0) : QObject(parent)
      {
          if (++instances == 1) {
              if (!timer)
                  timer = new MinuteTimer(QCoreApplication::instance());
              connect(timer, &MinuteTimer::timeChanged, this, &TimeModel::timeChanged);
              timer->start();
          }
      }

      ~TimeModel()
      {
          if (--instances == 0) {
              timer->stop();
          }
      }

      int minute() const { return timer->minute(); }
      int hour() const { return timer->hour(); }

  signals:
      void timeChanged();

  private:
      QTime t;
      static MinuteTimer *timer;
      static int instances;
  };

  int TimeModel::instances=0;
  MinuteTimer *TimeModel::timer=0;

  class QExampleQmlPlugin : public QQmlExtensionPlugin
  {
      Q_OBJECT
      Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)

  public:
      void registerTypes(const char *uri)
      {
          Q_ASSERT(uri == QLatin1String("TimeExample"));
          qmlRegisterType<TimeModel>(uri, 1, 0, "Time");
      }
  };

  #include "plugin.moc"