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{{KBCS}}
{{CodeSnippet
|id=CS001425
|platform=S60 3rd Edition, FP1, FP2<br>S60 5th Edition
|devices=Nokia 5800 XpressMusic
|category=Qt for Symbian
|subcategory=Base/System
|creationdate=June 16, 2009
|keywords=QPluginLoader, Q_DECLARE_INTERFACE, Q_INTERFACES, Q_EXPORT_PLUGIN2
}}

==Overview==

Qt applications can be extended with Qt plug-ins. This code snippet demonstrates how to load and initialise plug-ins dynamically in your application using <tt>QPluginLoader</tt>.

Defining the plug-in interface and implementing the plug-in are described in additional snippet articles.

'''Note''': In order to use this code, you need to have Qt for S60 installed on your platform.


==Important==

* When using Qt for S60 libraries from the (qt_libs_armv5_udeb.sisx) on a device, be sure to build both the plug-in and the loading application in '''DEBUG(UDEB)''' mode. This is because Qt uses a build key for each plug-in to ensure that only compatible plug-ins are loaded, and the build mode '''[debug|release]''' is part of that build key.

* In Symbian we have to define the variable <tt>EPOCALLOWDLLDATA</tt> as true for the plug-ins (library) because Qt macros have initialised global data; see the plug-in project files for more information.


==Preconditions==


==Project (.pro) file==

The DLL (plug-in) needs to have to have at least the same set of capabilities as the process (application) that loads the plug-in.

==Header (pluginwidget.h)==

Needed headers, methods and variables.
<code cpp>
// Qt plugin loader that loads plugins dynamically
#include <QPluginLoader>
#include <QtGui>
// Our defined plugin interface ExamplePluginInterface
#include "exampleplugininterface.h"

// Methods
bool loadPlugins(QString pluginDir);
void createPlugins();
void unloadPlugins();

private:
    // Arry to store all plugins
    QList<QPluginLoader*>   plugins;
</code>


==Source (yourapp.cpp)==

Load the plug-ins.
<code cpp>
bool YourApp::loadPlugins(QString pluginDir)
    {
    QDir pluginsDir(QLibraryInfo::location
    (QLibraryInfo::PluginsPath));

    // "exampleplugins" is the folder where you are exported plugins
    // by Qt macro Q_EXPORT_PLUGIN2(exampleplugins, YourPlugin);
    pluginsDir.cd("exampleplugins");

    foreach (QString fileName, pluginsDir.entryList(QDir::Files))
        {
        // Create plugin loader
        QPluginLoader* pluginLoader = 
        new QPluginLoader(pluginsDir.absoluteFilePath(fileName));
        // Store loader to array
        plugins.append(pluginLoader);
        // Load plugin
        bool ret = pluginLoader->load();
        if (!ret)
            {
            QMessageBox::information(this, "YourApp", 
            QString("Could not load plugin %1").arg(fileName));
            }
        }

    // Did we found any plugins?
    if (plugins.isEmpty())
        return false;
    else
        return true;
    }
</code>

Create the plug-ins.
<code cpp>
void YourApp::createPlugins()
    {
    // Show data of all media plugins in different tabs
    for (int i=0 ; i<plugins.count() ; i++)
        {
        QPluginLoader* pluginLoader = plugins[i];
        // Create plugin instance
        QObject *plugin = pluginLoader->instance();
        if (plugin)
            {
            // Plugin instance created

            // Cast plugin to ExamplePluginInterface,
            // that is common for all plugins
            ExamplePluginInterface* pluginIF
            = qobject_cast<ExamplePluginInterface*>(plugin);

            // Signal / slot, if needed
            //QObject::connect(this, SIGNAL(send(QString *)),
            //        pluginIF, SLOT(someSlot(QString *)));
            }
        else
            {
            // Could not create plugin instance, delete pluginloader
            delete pluginLoader;
            plugins.removeAt(i);
            i--;
            }
        }
    }
</code>

Unload the plug-ins.
<code cpp>
void YourApp::unloadPlugins()
    {
    // Unload plugins and clear plugin array
    foreach (QPluginLoader* pluginLoader, plugins)
        {
        pluginLoader->unload();
        delete pluginLoader;
        }   
    plugins.clear();
    }
</code>



==See also==

* [[CS001390 - Defining a Qt plug-in interface]]
* [[CS001391 - Implementing the Qt plug-in interface]]

* For more information about plug-ins, see [http://doc.qtsoftware.com/4.5/plugins-howto.html How to Create Qt Plugins].


==Postconditions==
The Qt plug-in is loaded and initialised dynamically.


[[Category:Qt]][[Category:Qt for Symbian]][[Category:Code Examples]][[Category:Base/System]]