KDE 4.1.2 here.
I want to have a ShowDesktop icon in the quicklauncher plasmoid that I have placed next to the icon of K menu.
The ShowDesktop widget that now sits next to the quicklauncher takes too much place (I like small icons like those of quicklaunch in Windows XP and Vista).
Dragging the ShowDesktop widget to the quicklauncher doesn't work as the quicklauncher widget can't work with "services", it expects a .desktop file with an exec command.
In KDE 3.5.9 I could do this with a dcop command.

qdbusviewer shows that there are no dbus methods for toggling showdesktop.
I looked at the source code of plasma_applet_showdesktop.so:

Code: Select all

NETRootInfo info(QX11Info::display(), 0);
 ...
info.setShowingDesktop(m_down);    //m_down is a boolean


I fear I have to write my own C++ code to be able to toggle showdesktop with a click on an icon in quicklauncher but I don't know anything yet about the plasma source code.
I'll ask this question also in plasma-devel mailing list.
If there is no existing command I'll file a wish request at bugs.kde.org

Aseigo replied to me in plasma-devel mailing list that there is no existing command.
I filed a wish report at https://bugs.kde.org/show_bug.cgi?id=173759 .
I also noticed at http://techbase.kde.org/Schedules/KDE4/4.2_Feature_Plan that dbus interface for plasma is a TO DO.