Inherits QObject.
The session manager is responsible for session management, most importantly for interruption and resumption. A "session" is a kind of record of the state of the system, e.g. which applications were run at start up and which applications are currently running. 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. Use QSettings to save and restore an individual application's settings, e.g. window positions, recently used files, etc.
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.
During a session management action (i.e. within commitData() and saveState()), no user interaction is possible unless the application got 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 possibilites to fine-tune an application's session management behavior: setRestartCommand(), setDiscardCommand(), setRestartHint(), setProperty(), requestPhase2(). See the respective function descriptions for further details.
See also Main Window and Related Classes and Environment Classes.
The default hint is RestartIfRunning.
See also allowsInteraction(), release(), and cancel().
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& sm ) {
if ( sm.allowsInteraction() ) {
switch ( QMessageBox::warning(
yourMainWindow,
tr("Application Name"),
tr("Save changes to document Foo?"),
tr("&Yes"),
tr("&No"),
tr("Cancel"),
0, 2) ) {
case 0: // yes
sm.release();
// save document here; if saving fails, call sm.cancel()
break;
case 1: // continue without saving
break;
default: // cancel
sm.cancel();
break;
}
} 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().
See also allowsInteraction() and allowsErrorInteraction().
Note that if you want to iterate over the list, you should iterate over a copy, e.g.
QStringList list = mySession.discardCommand();
QStringList::Iterator it = list.begin();
while( it != list.end() ) {
myProcessing( *it );
++it;
}
See also setDiscardCommand(), restartCommand(), and setRestartCommand().
See also allowsInteraction() and allowsErrorInteraction().
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.
Note that if you want to iterate over the list, you should iterate over a copy, e.g.
QStringList list = mySession.restartCommand();
QStringList::Iterator it = list.begin();
while( it != list.end() ) {
myProcessing( *it );
++it;
}
See also setRestartCommand() and restartHint().
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().
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().
The property called name has its value set to the string list value.
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.
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().
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().