Development/Tutorials/Plasma4/ApplicationShell

This page looks at the steps it takes to embed a Plasma shell inside of your application as a dashboard or summary page.

The Shell

The core of the dashboard's logic is in a KPart in kdebase-runtime (Currently still in playground/base/plasma/shells/kpart), plasma-kpart. This KPart is loaded like any other ReadOnly KPart:

// this routine will find and load our Part.  it finds the Part by
// name which is a bad idea usually.. but it's alright in this
// case since our Part is made for this Shell
KService::Ptr service = KService::serviceByDesktopPath( "plasma-kpart.desktop" );

if (service)
{  
    // now that the Part is loaded, we cast it to a Part to get
    // our hands on it
    m_part = service->createInstance<KParts::ReadOnlyPart>(0, args);
    if (m_part)
    {   
        // tell the KParts::MainWindow that this is indeed the main widget
        // If you have something better to do with the widget, this is where
        // you would do it.
        setCentralWidget(m_part->widget());

        // and integrate the part's GUI with the shell's
        createGUI(m_part);

    }   
    else
    {   
        // For whatever reason the part didn't load
        KMessageBox::error(this, i18n("Could not instantiate our Part!"));
        qApp->quit();
    }   
}   
else
{   
    // if we couldn't find our Part, we exit since the Shell by
    // itself can't do anything useful
    KMessageBox::error(this, i18n("Could not find our Part!"));
    qApp->quit();
    // we return here, cause qApp->quit() only means "exit the
    // next time we enter the event loop...
    return;
}

The Applets

There are two ways to approach writing applets, and some thought should go into this before writing your applets. The first is to use the standard method of writing Plasma applets, and provide a DataEngine which your applets can use to communicate with your application, either via DBus (allowing you to use the applets on the desktop and in other shells) or intra-process signal/slots using the PluginLoader infrastructure.

• Pros:
  • Applets can be scripted in Javascript or Python
  • Applets get all of the For Free benefits of being subclasses of Plasma::Applet
• Cons:
  • Requires writing applets from scratc

The second method is to wrap QWidgets inside of a Plasma::Applet using a QGraphicsProxyWidget. This is most useful if your application has an existing dashboard which is not based on Plasma.

• Pros:
  • No need to learn a new API to build widgets
  • Closer integration with applications
  • Can re-use pre-existing applets
• Cons:
  • No Plasma theming
  • No access to DataEngines and other Plasma services