Home

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:

 /****************************************************************************
 **
 ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the Qt Solutions component.
 **
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
 **     the names of its contributors may be used to endorse or promote
 **     products derived from this software without specific prior written
 **     permission.
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ****************************************************************************/

 #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_OS_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();
 }