Development/Tutorials/Session Management: Difference between revisions

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    This tutorial was updated and moved to https://develop.kde.org/docs/configuration/introduction/


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    [[Category:MovedDevelop]]
     
    ==About KDE and X11 session management==
     
    KDE supports the legacy X11R4 and ICCCM session
    management protocols.  Legacy applications that define the <tt>WM_COMMAND</tt>
    property or support the <tt>WM_SAVE_YOURSELF</tt> protocol will be restarted
    with the specified command.  The window geometries will be restored on a best
    effort basis.
     
    Since version 2.0, KDE also supports and uses the standard X11R6
    session management protocol XSMP. The official documentation of the
    standard can be download from the X Consortium's FTP server
    [http://stuff.mit.edu/afs/sipb/contrib/doc/X11/hardcopy/SM/xsmp.PS.gz ftp.x.org].
     
    Unlike these legacy protocols, the new X11R6 session management gives a
    chance to save application dependent settings when you log out.  A text
    editor, for instance, would save the names of the loaded files and would
    reload them when you log in again.  Another major advantage of the new
    protocol is the support for a clean and safe logout procedure even if the
    users decides not to restore the session next time. The protocol gives
    applications the possibility to interact with the user in case they are in
    danger to lose some data, and to cancel the shutdown process if necessary.
     
    ==Further Reading==
     
    An introductive overview of session management functionality and
    the Qt API for it is available from [http://doc.trolltech.com/4.4/session.html doc.trolltech.com].
     
    In KDE, the classes [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKApplication.html KApplication]
    and [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow]
    hide all the ugly details from the programmer. Basically, a
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKApplication.html KApplication] manages a
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdecore/html/classKConfig.html KConfig] configuration object
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKApplication.html#8f88369c240d6d90a04d29b2761989d9 sessionConfig()]
    for you, that your application can utilize to store session specific data.
     
    Please read the respective class documentation, especially the one of
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], for a detailed interface description. With the advanced
    functionality in [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], it's really just a matter of a few lines to get even a multi-window application to retains its state between
    different user sessions.
     
    ==Implementing session management in your application==
     
    Here's just a brief overview how things are done. Again, see the
    respective class documentation for details.
     
    ===Add session management support to your main() function===
     
    ====For one kind of toplevel widget====
     
    If your client has only one kind of toplevel widgets (which should be pretty usual) then you should use the RESTORE-macro for backwards compatibility with 3.1 and 3.0 branches.
     
    Imagine you have an
    application with a main window MyWindow inherited from
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow] (or from
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKXmlGuiWindow.html KXmlGuiWindow], which inherits from
    [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow]). In your main() function, you would then create/restore the
    application windows with something like:
     
    <code cppqt>
    KApplication app;
    if ( kapp->isSessionRestored() ) {
      RESTORE( MyWindow )
    } else {
      // create default application as usual
      // for example:
      MyWindow* window = new MyWindow();
      window->show();
    }
    return app.exec();
    </code>
     
    Note that QWidget::show() is called implicitly in RESTORE.
     
    With this you can easily restore all toplevel windows of your application.
     
    ====For several kinds of toplevel widgets====
     
    It is also possible to
    restore different types of toplevel windows within one application. In
    that case, the RESTORE macro is too primitive. If you have more than one
    kind of toplevel widget (each derived from [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], of course), you
    can use the templated kRestoreMainWindows global functions:
     
    <code cppqt>
    KApplication app;
    if ( kapp->isSessionRestored() ) {
      kRestoreMainWindows< childMW1, childMW2, childMW3 >();
    } else {
      // create default application as usual
      // for example:
      childMW1* window1 = new childMW1();
      childMW2* window2 = new childMW2();
      childMW3* window3 = new childMW3();
      window1->show();
      window2->show();
      window3->show();
    }
    return app.exec();
    </code>
     
    Currently, these functions are provided for up to three template arguments.
     
    ===Reimplement some virtual functions of KMainWindow===
     
    KMainWindow will save its position, geometry and positions of toolbars and menubar on logout. To save additional data, reimplement saveProperties() and (to read them again on next login) readProperties(). (For a text editor, that would be the loaded files, for example.) To warn the user that the application or some windows have unsaved data on close or logout, reimplement queryClose().
     
    To save special data about your data, reimplement saveGlobalProperties().
     
    ==Appendix: Architecture of the KDE session manager==
     
    The session management server in KDE is called '''ksmserver''' and it is
    part of the '''kdebase''' package.  The server interacts with the KDE window
    manager '''kwin''' to save and restore the window geometries and to perform
    legacy session management.  To make session management work, '''ksmserver'''
    has to be started as last process of the X login procedure. This happens
    automatically at the end of the '''startkde''' script.
     
     
    ''Initial Author:'' [mailto:[email protected] Matthias Ettrich]
     
    [[Category:Programming]]
    [[Category:Tutorial]]
    [[Category:FAQs]]

    Revision as of 09:36, 4 October 2020

    This tutorial was updated and moved to https://develop.kde.org/docs/configuration/introduction/