From Forum Nokia Wiki

ID	CS001425	Creation date	June 16, 2009
Platform	S60 3rd Edition, FP1, FP2 S60 5th Edition	Tested on devices	Nokia 5800 XpressMusic
Category	Qt for Symbian	Subcategory	Base/System

Keywords (APIs, classes, methods, functions): 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 QPluginLoader.

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 EPOCALLOWDLLDATA 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.

// 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;

Source (yourapp.cpp)

Load the plug-ins.

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;
    }

Create the plug-ins.

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--;
            }
        }
    }

Unload the plug-ins.

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

See also

• CS001390 - Defining a Qt plug-in interface
• CS001391 - Implementing the Qt plug-in interface

• For more information about plug-ins, see How to Create Qt Plugins.

Postconditions

The Qt plug-in is loaded and initialised dynamically.