QSessionManager Class Reference
^{[QtGui module]}

Detailed Description

The QSessionManager class provides access to the session manager.

A session manager in a desktop environment (in which Qt GUI applications live) keeps track of a session, which is a group of running applications, each of which has a particular state. The state of an application contains (most notably) the documents the application has open and the position and size of its windows.

The session manager is used to save the session, e.g. when the machine is shut down, and to restore a session, e.g. when the machine is started up. We recommend that you use QSettings to save an individual application's settings, e.g. window positions, recently used files, etc. When the application is restarted by the session manager, you can restore the settings.

QSessionManager provides an interface between the application and the session manager so that the program can work well with the session manager. In Qt, session management requests for action are handled by the two virtual functions QApplication::commitData() and QApplication::saveState(). Both provide a reference to a session manager object as argument, to allow the application to communicate with the session manager. The session manager can only be accessed through these functions.

No user interaction is possible unless the application gets explicit permission from the session manager. You ask for permission by calling allowsInteraction() or, if it's really urgent, allowsErrorInteraction(). Qt does not enforce this, but the session manager may.

You can try to abort the shutdown process by calling cancel(). The default commitData() function does this if some top-level window rejected its closeEvent().

For sophisticated session managers provided on Unix/X11, QSessionManager offers further possibilities to fine-tune an application's session management behavior: setRestartCommand(), setDiscardCommand(), setRestartHint(), setProperty(), requestPhase2(). See the respective function descriptions for further details.

See also QApplication and Session Management.

Member Type Documentation

enum QSessionManager::RestartHint

This enum type defines the circumstances under which this application wants to be restarted by the session manager. The current values are

The default hint is RestartIfRunning.

Member Function Documentation

bool QSessionManager::allowsErrorInteraction ()

Returns true if error interaction is permitted; otherwise returns false.

This is similar to allowsInteraction(), but also enables the application to tell the user about any errors that occur. Session managers may give error interaction requests higher priority, which means that it is more likely that an error interaction is permitted. However, you are still not guaranteed that the session manager will allow interaction.

See also allowsInteraction(), release(), and cancel().

bool QSessionManager::allowsInteraction ()

Asks the session manager for permission to interact with the user. Returns true if interaction is permitted; otherwise returns false.

The rationale behind this mechanism is to make it possible to synchronize user interaction during a shutdown. Advanced session managers may ask all applications simultaneously to commit their data, resulting in a much faster shutdown.

When the interaction is completed we strongly recommend releasing the user interaction semaphore with a call to release(). This way, other applications may get the chance to interact with the user while your application is still busy saving data. (The semaphore is implicitly released when the application exits.)

If the user decides to cancel the shutdown process during the interaction phase, you must tell the session manager that this has happened by calling cancel().

Here's an example of how an application's QApplication::commitData() might be implemented:

 void MyApplication::commitData(QSessionManager& manager)
 {
     if (manager.allowsInteraction()) {
         int ret = QMessageBox::warning(
                     mainWindow,
                     tr("My Application"),
                     tr("Save changes to document?"),
                     QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel);

         switch (ret) {
         case QMessageBox::Save:
             manager.release();
             if (!saveDocument())
                 manager.cancel();
             break;
         case QMessageBox::Discard:
             break;
         case QMessageBox::Cancel:
         default:
             manager.cancel();
         }
     } else {
         // we did not get permission to interact, then
         // do something reasonable instead
     }
 }

If an error occurred within the application while saving its data, you may want to try allowsErrorInteraction() instead.

See also QApplication::commitData(), release(), and cancel().

void QSessionManager::cancel ()

Tells the session manager to cancel the shutdown process. Applications should not call this function without first asking the user.

See also allowsInteraction() and allowsErrorInteraction().

QStringList QSessionManager::discardCommand () const

Returns the currently set discard command.

To iterate over the list, you can use the foreach pseudo-keyword:

 foreach (QString command, mySession.discardCommand())
     do_something(command);

See also setDiscardCommand(), restartCommand(), and setRestartCommand().

bool QSessionManager::isPhase2 () const

Returns true if the session manager is currently performing a second session management phase; otherwise returns false.

See also requestPhase2().

void QSessionManager::release ()

Releases the session manager's interaction semaphore after an interaction phase.

See also allowsInteraction() and allowsErrorInteraction().

void QSessionManager::requestPhase2 ()

Requests a second session management phase for the application. The application may then return immediately from the QApplication::commitData() or QApplication::saveState() function, and they will be called again once most or all other applications have finished their session management.

The two phases are useful for applications such as the X11 window manager that need to store information about another application's windows and therefore have to wait until these applications have completed their respective session management tasks.

Note that if another application has requested a second phase it may get called before, simultaneously with, or after your application's second phase.

See also isPhase2().

QStringList QSessionManager::restartCommand () const

Returns the currently set restart command.

To iterate over the list, you can use the foreach pseudo-keyword:

 foreach (QString command, mySession.restartCommand())
     do_something(command);

See also setRestartCommand() and restartHint().

RestartHint QSessionManager::restartHint () const

Returns the application's current restart hint. The default is RestartIfRunning.

See also setRestartHint().

QString QSessionManager::sessionId () const

Returns the identifier of the current session.

If the application has been restored from an earlier session, this identifier is the same as it was in that earlier session.

See also sessionKey() and QApplication::sessionId().

QString QSessionManager::sessionKey () const

Returns the session key in the current session.

If the application has been restored from an earlier session, this key is the same as it was when the previous session ended.

The session key changes with every call of commitData() or saveState().

See also sessionId() and QApplication::sessionKey().

void QSessionManager::setDiscardCommand ( const QStringList & list )

Sets the discard command to the given list.

See also discardCommand() and setRestartCommand().

void QSessionManager::setManagerProperty ( const QString & name, const QStringList & value )

Low-level write access to the application's identification and state record are kept in the session manager.

The property called name has its value set to the string list value.

void QSessionManager::setManagerProperty ( const QString & name, const QString & value )

This is an overloaded member function, provided for convenience.

Low-level write access to the application's identification and state records are kept in the session manager.

The property called name has its value set to the string value.

void QSessionManager::setRestartCommand ( const QStringList & command )

If the session manager is capable of restoring sessions it will execute command in order to restore the application. The command defaults to

 appname -session id

The -session option is mandatory; otherwise QApplication cannot tell whether it has been restored or what the current session identifier is. See QApplication::isSessionRestored() and QApplication::sessionId() for details.

If your application is very simple, it may be possible to store the entire application state in additional command line options. This is usually a very bad idea because command lines are often limited to a few hundred bytes. Instead, use QSettings, or temporary files or a database for this purpose. By marking the data with the unique sessionId(), you will be able to restore the application in a future session.

See also restartCommand(), setDiscardCommand(), and setRestartHint().

void QSessionManager::setRestartHint ( RestartHint hint )

Sets the application's restart hint to hint. On application startup the hint is set to RestartIfRunning.

Note that these flags are only hints, a session manager may or may not respect them.

We recommend setting the restart hint in QApplication::saveState() because most session managers perform a checkpoint shortly after an application's startup.

See also restartHint().