QtSingleApplication Class Reference

The QtSingleApplication class provides an API to detect and communicate with running instances of an application. More...

#include <qtsingleapplication.h>

List of all members.

Public Slots

bool sendMessage (const QString &message, int timeout=5000)
void activateWindow ()

Signals

void messageReceived (const QString &message)

Public Member Functions

 QtSingleApplication (int &argc, char **argv, bool GUIenabled=true)
 QtSingleApplication (const QString &id, int &argc, char **argv)
 QtSingleApplication (int &argc, char **argv, Type type)
bool isRunning ()
QString id () const
void setActivationWindow (QWidget *aw, bool activateOnMessage=true)
QWidget * activationWindow () const
void initialize (bool dummy=true)

Private Member Functions

void sysInit (const QString &appId=QString())

Private Attributes

QtLocalPeerpeer
QWidget * actWin


Detailed Description

The QtSingleApplication class provides an API to detect and communicate with running instances of an application.

This class allows you to create applications where only one instance should be running at a time. I.e., if the user tries to launch another instance, the already running instance will be activated instead. Another usecase is a client-server system, where the first started instance will assume the role of server, and the later instances will act as clients of that server.

By default, the full path of the executable file is used to determine whether two processes are instances of the same application. You can also provide an explicit identifier string that will be compared instead.

The application should create the QtSingleApplication object early in the startup phase, and call isRunning() or sendMessage() to find out if another instance of this application is already running. Startup parameters (e.g. the name of the file the user wanted this new instance to open) can be passed to the running instance in the sendMessage() function.

If isRunning() or sendMessage() returns false, it means that no other instance is running, and this instance has assumed the role as the running instance. The application should continue with the initialization of the application user interface before entering the event loop with exec(), as normal. The messageReceived() signal will be emitted when the application receives messages from another instance of the same application.

If isRunning() or sendMessage() returns true, another instance is already running, and the application should terminate or enter client mode.

If a message is received it might be helpful to the user to raise the application so that it becomes visible. To facilitate this, QtSingleApplication provides the setActivationWindow() function and the activateWindow() slot.

Here's an example that shows how to convert an existing application to use QtSingleApplication. It is very simple and does not make use of all QtSingleApplication's functionality (see the examples for that).

    // Original
    int main(int argc, char **argv)
    {
        QApplication app(argc, argv);

        MyMainWidget mmw;

        mmw.show();
        return app.exec();
    }

    // Single instance
    int main(int argc, char **argv)
    {
        QtSingleApplication app(argc, argv);

        if (app.isRunning())
            return 0;

        MyMainWidget mmw;

        app.setActivationWindow(&mmw);

        mmw.show();
        return app.exec();
    }

Once this QtSingleApplication instance is destroyed(for example, when the user quits), when the user next attempts to run the application this instance will not, of course, be encountered. The next instance to call isRunning() or sendMessage() will assume the role as the new running instance.

For console (non-GUI) applications, QtSingleCoreApplication may be used instead of this class, to avoid the dependency on the QtGui library.

See also:
QtSingleCoreApplication

Constructor & Destructor Documentation

QtSingleApplication::QtSingleApplication ( int &  argc,
char **  argv,
bool  GUIenabled = true 
)

Creates a QtSingleApplication object. The application identifier will be QCoreApplication::applicationFilePath(). argc, argv, and GUIenabled are passed on to the QAppliation constructor.

If you are creating a console application (i.e. setting GUIenabled to false), you may consider using QtSingleCoreApplication instead.

QtSingleApplication::QtSingleApplication ( const QString &  appId,
int &  argc,
char **  argv 
)

Creates a QtSingleApplication object with the application identifier appId. argc and argv are passed on to the QAppliation constructor.

QtSingleApplication::QtSingleApplication ( int &  argc,
char **  argv,
Type  type 
)

Creates a QtSingleApplication object. The application identifier will be QCoreApplication::applicationFilePath(). argc, argv, and type are passed on to the QAppliation constructor.


Member Function Documentation

void QtSingleApplication::activateWindow (  )  [slot]

De-minimizes, raises, and activates this application's activation window. This function does nothing if no activation window has been set.

This is a convenience function to show the user that this application instance has been activated when he has tried to start another instance.

This function should typically be called in response to the messageReceived() signal. By default, that will happen automatically, if an activation window has been set.

See also:
setActivationWindow(), messageReceived(), initialize()

QWidget * QtSingleApplication::activationWindow (  )  const

Returns the applications activation window if one has been set by calling setActivationWindow(), otherwise returns 0.

See also:
setActivationWindow()

QString QtSingleApplication::id (  )  const

Returns the application identifier. Two processes with the same identifier will be regarded as instances of the same application.

void QtSingleApplication::initialize ( bool  dummy = true  )  [inline]

bool QtSingleApplication::isRunning (  ) 

Returns true if another instance of this application is running; otherwise false.

This function does not find instances of this application that are being run by a different user (on Windows: that are running in another session).

See also:
sendMessage()

void QtSingleApplication::messageReceived ( const QString &  message  )  [signal]

This signal is emitted when the current instance receives a message from another instance of this application.

See also:
sendMessage(), setActivationWindow(), activateWindow()

bool QtSingleApplication::sendMessage ( const QString &  message,
int  timeout = 5000 
) [slot]

Tries to send the text message to the currently running instance. The QtSingleApplication object in the running instance will emit the messageReceived() signal when it receives the message.

This function returns true if the message has been sent to, and processed by, the current instance. If there is no instance currently running, or if the running instance fails to process the message within timeout milliseconds, this function return false.

See also:
isRunning(), messageReceived()

void QtSingleApplication::setActivationWindow ( QWidget *  aw,
bool  activateOnMessage = true 
)

Sets the activation window of this application to aw. The activation window is the widget that will be activated by activateWindow(). This is typically the application's main window.

If activateOnMessage is true (the default), the window will be activated automatically every time a message is received, just prior to the messageReceived() signal being emitted.

See also:
activateWindow(), messageReceived()

void QtSingleApplication::sysInit ( const QString &  appId = QString()  )  [private]


Member Data Documentation

QWidget* QtSingleApplication::actWin [private]


The documentation for this class was generated from the following files:

Generated on Sun Jun 14 15:11:35 2009 for PLCEdit by  doxygen 1.5.9