QSessionManager Class Reference
The QSessionManager class provides access to the session manager.
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#include <qsessionmanager.h>
Inherits QObject.
List of all member functions.
Public Members
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RestartHint { RestartIfRunning, RestartAnyway, RestartImmediately, RestartNever }
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Detailed Description
The QSessionManager class provides access to the session manager.
The session manager is responsible for session management, most
importantly interruption and resumption.
QSessionManager provides an interface between the application and
the session manager, so that the program can work well with the
session manager. In Qt, the session management requests for action
are handled by the two virtual functions QApplication::commitData()
and QApplication::saveState(). Both functions provide a reference to
a session manager object as argument, thus allowing the application
to communicate with the session manager.
During a session management action, i.e. within one of the two
mentioned functions, no user interaction is possible, unless the
application got explicit permission from the session manager. You
can ask for permission by calling allowsInteraction() or, if it's
really urgent, allowsErrorInteraction(). Qt does not enforce this,
but the session manager may. Perhaps.
You can try to abort the shutdown process by calling cancel. The
default commitData() function does that if some top-level window
rejected its closeEvent().
For sophisticated session managers as provided on Unix/X11,
QSessionManager offers further possibilities to fine-tune an
application's session management behaviour: setRestartCommand(),
setDiscardCommand(), setRestartHint(), setProperty(),
requestPhase2(). Please see the respective function descriptions
for further details.
Member Type Documentation
This enum type defines the circumstances under which this
application wants to be restarted by the session manager. The
current values are:
-
RestartIfRunning - if the application still runs by the time
the session is shut down, it wants to be restarted at the start of
the next session.
-
RestartAnyway - the application wants to be started at the
start of the next session, no matter what. (This is useful for
utilities that run just after startup, then quit.)
-
RestartImmediately - the application wants to be started
immediately whenever it is not running.
-
RestartNever - the application does not want to be restarted
automatically.
The default hint is RestartIfRunning.
Member Function Documentation
bool QSessionManager::allowsErrorInteraction ()
Like allowsInteraction() but tells the session manager in addition
that an error occurred. Session managers may give error interaction
request higher priority. That means it is more likely that an error
interaction is granted. However, you are still not guaranteed that
the session manager will grant your request.
See also allowsInteraction(), release() and cancel().
bool QSessionManager::allowsInteraction ()
Asks the session manager for permission to interact with the
user. Returns TRUE if the interaction was granted, FALSE
otherwise.
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 done 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 so by calling
cancel().
Here's an example usage of the mentioned functions that may occur
in the QApplication::commitData() function of an application:
void MyApplication::commitData( QSessionManager& sm ) {
if ( sm.allowsInteraction() ) {
switch ( QMessageBox::warning( yourMainWindow, "Application Name",
"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: // no
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().
void QSessionManager::cancel ()
Tells the session manager to cancel the shutdown process. Applications
should not call this function without asking the user first.
See also allowsInteraction() and allowsErrorInteraction().
QStringList QSessionManager::discardCommand () const
Returns the currently set discard command.
See also setDiscardCommand(), restartCommand() and setRestartCommand().
bool QSessionManager::isPhase2 () const
Returns whether the session manager is currently performing a second
session management phase.
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/all other applications have
finished their session management.
The two phases are useful for applications like X11 window manager,
that need to store informations about other application's windows
and therefore have to wait until these applications finished 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.
See also setRestartCommand() and restartHint().
QSessionManager::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 previous session.
See also QApplication::sessionId().
void QSessionManager::setDiscardCommand ( const QStringList & )
See also discardCommand() and setRestartCommand().
void QSessionManager::setProperty ( const QString & name, const QString & value )
Low-level write access to the application's identification and state
record kept in the session manager.
void QSessionManager::setProperty ( const QString & name, const QStringList & value )
Low-level write access to the application's identification and state
record kept in the session manager.
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 can not
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. In general, this is a very bad
idea, since command lines are often limited to a few hundred bytes.
Instead, use 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
start-up the hint is set to RestartIfRunning.
Note that these flags are only hints, a session manager may or may
not obey them.
We recommend setting the restart hint in QApplication::saveState()
since most session managers perform a checkpoint shortly after an
application's startup.
See also restartHint().
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