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An Interactive Service

This example implements a service with a simple user interface.

Services are usually non-interactive console applications. User interaction, if required, is usually implemented in a separate, normal GUI application that communicates with the service through an IPC channel. For simple communication, QtServiceController::sendCommand() and QtService::processCommand() may be used, possibly in combination with a shared settings file. For more complex, interactive communication, a custom IPC channel should be used, e.g. based on Qt's networking classes.

However, although not recommended in the general case, in certain circumstances a service may provide a GUI itself. This is typically only possible if the service process is run as the same user as the one that is logged in, so that it will have access to the screen. Note however that on Windows Vista, service GUIs are not allowed at all, since services run in a diferent session than all user sessions, for security reasons.

This example demonstrates how to subclass the QtService class, the use of start(), stop(), pause(), resume(), and how to use processCommand() to receive control commands while running.

Here is the complete source code:

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 #include <QtGui/QApplication>
 #include <QtGui/QDesktopWidget>
 #include <QtGui/QLabel>
 #include <QtCore/QDir>
 #include <QtCore/QSettings>
 #include "qtservice.h"

 class InteractiveService : public QtService<QApplication>
 {
 public:
     InteractiveService(int argc, char **argv);
     ~InteractiveService();

 protected:

     void start();
     void stop();
     void pause();
     void resume();
     void processCommand(int code);

 private:
     QLabel *gui;
 };

 InteractiveService::InteractiveService(int argc, char **argv)
     : QtService<QApplication>(argc, argv, "Qt Interactive Service"), gui(0)
 {
     setServiceDescription("A Qt service with user interface.");
     setServiceFlags(QtServiceBase::CanBeSuspended);
 }

 InteractiveService::~InteractiveService()
 {
 }

 void InteractiveService::start()
 {
 #if defined(Q_OS_WIN)
     if ((QSysInfo::WindowsVersion & QSysInfo::WV_NT_based) &&
         (QSysInfo::WindowsVersion >= QSysInfo::WV_VISTA)) {
         logMessage( "Service GUI not allowed on Windows Vista. See the documentation for this example for more information.", QtServiceBase::Error );
         return;
     }
 #endif

     qApp->setQuitOnLastWindowClosed(false);

     gui = new QLabel("Service", 0, Qt::WindowStaysOnTopHint | Qt::FramelessWindowHint);
     gui->move(QApplication::desktop()->availableGeometry().topLeft());
     gui->show();
 }

 void InteractiveService::stop()
 {
     delete gui;
 }

 void InteractiveService::pause()
 {
     if (gui)
         gui->hide();
 }

 void InteractiveService::resume()
 {
     if (gui)
         gui->show();
 }

 void InteractiveService::processCommand(int code)
 {
     gui->setText("Command code " + QString::number(code));
     gui->adjustSize();
 }

 int main(int argc, char **argv)
 {
 #if !defined(Q_WS_WIN)
     // QtService stores service settings in SystemScope, which normally require root privileges.
     // To allow testing this example as non-root, we change the directory of the SystemScope settings file.
     QSettings::setPath(QSettings::NativeFormat, QSettings::SystemScope, QDir::tempPath());
     qWarning("(Example uses dummy settings file: %s/QtSoftware.conf)", QDir::tempPath().toLatin1().constData());
 #endif
     InteractiveService service(argc, argv);
     return service.exec();
 }