Archive:Development/Tutorials/Session Management (zh CN)

Development/Tutorials/Session Management

关于KDE和X11会话管理

Since KDE 1.0, the legacy X11R4 and ICCCM session management protocols are supported. Legacy applications that define the WM_COMMAND property or support the WM_SAVE_YOURSELF protocol will be restarted with the specified command. The window geometries will be restored on a best effort basis.

Since KDE 2.0, also the standard X11R6 session management protocol XSMP is supported and used. The official documentation of the standard can be download from the X Consortium's FTP server 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.

Implementing session management in your application

Here's just a brief overview how things are done. Again, see the respective class documentation for details.

Implementing session management in KDE is easy. If your main window inherits from KMainWindow, you have just 2 things to do:

Reimplement some virtual functions of KMainWindow.
Add session management support to your main() function.

That's all.

Reimplement some virtual functions of KMainWindow

KMainWindow will save its position, geometry and positions of toolbars and menubar on logout.

To warn the user that the application or some windows have unsaved data on close or logout (for example: show a dialog with the buttons "Save changes" and "Discard changes"), reimplement queryClose().
To save additional data, reimplement saveProperties(). (For a text editor, that would be the loaded files, for example.) Note that no user interaction is allowed in this function! For example, you may not display any dialog!
To read the additional data again on next login, reimplement readProperties().

These functions are called automatically by KMainWindow respectively by the session manager. Note that it is not determined if saveProperties() is called before or after queryClose()! Please read documentation of the respective functions before reimplementing them.

To save your application-wide properties (data that is only needed once per application, and not for each main window) reimplement saveGlobalProperties() and it's counterpart readGlobalProperties. Normally, you don't need these functions.

在main()函数添加会话管理

While KMainWindow::saveProperties() and KMainWindow::queryClose() will work out of the box, KMainWindow::readProperties() will not. You have to add some code to your main() function to implement session restoring.

Imagine you have an application with a main window MyWindow inherited from KMainWindow (or from KXmlGuiWindow, which inherits from KMainWindow). In your main() function, you would then create/restore the application windows with something like:

KApplication app; if ( app.isSessionRestored() ) {

 kRestoreMainWindows< MyWindow >();

} else {

 // create default application as usual
 // for example:
 MyWindow * window = new MyWindow();
 // # will be replaced with numbers that are guaranteed
 // to be unique in the application:
 window->setObjectName("MyWindow#");
 window->show();

} return app.exec();

kRestoreMainWindows<>() will create (on the heap) as many instances of your main windows as have existed in the last session and call KMainWindow::restore() with the correct arguments. Note that also QWidget::show() is called implicitly.

About setObjectName("MyWindow#"): For session management and window management to work properly, all main windows in the application should have a different name. If you don't do it, KMainWindow will create a unique name, but it's recommended to explicitly pass a window name that will also describe the type of the window. If there can be several windows of the same type, append '#' (hash) to the name, and KMainWindow will replace it with numbers to make the names unique. For example, for a mail client which has one main window showing the mails and folders, and which can also have one or more windows for composing mails, the name for the folders window should be e.g. "mainwindow" and for the composer windows "composer#".

With this you can easily restore all toplevel windows of your application.

It is also possible to restore different types of toplevel windows (each derived from KMainWindow, of course) within one application. Imagine you have three classes of main windows: childMW1, childMW2 and childMW3:

KApplication app; if ( app.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();
 // # will be replaced with numbers that are guaranteed
 // to be unique in the application:
 window1->setObjectName("type1mainWindow#");
 window2->setObjectName("type2mainWindow#");
 window3->setObjectName("type3mainWindow#");
 window1->show();
 window2->show();
 window3->show();

} return app.exec();

现在, kRestoreMainWindows<>()的方法模版提供最多三个模版参数。

附录: KDE会话管理架构

KDE的会话管理服务器叫做ksmserver，他是kdebase的一部分。服务进程与KDE的窗口管理服务进程kwin进行交互，保存和恢复窗口信息，进行遗留的会话管理。要启用会话管理, ksmserver必须X登陆过程的最后一个进程。这个会在startkde脚本的末尾体现.

初始作者: Matthias Ettrich