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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><!-- /home/edba/dist/qtopia/main-Sunday/qtopia/doc/pluginintro.doc:1 --><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Qtopia Plugins</title><style type="text/css"><!--h3.fn,span.fn { margin-left: 1cm; text-indent: -1cm; }a:link { color: #004faf; text-decoration: none }a:visited { color: #672967; text-decoration: none }body { background: #ffffff; color: black; }--></style></head><body><table border="0" cellpadding="0" cellspacing="0" width="100%"><tr><td width="200" align="left" valign="top"><a href="index.html"><img height="27" width="472" src="dochead.png" border="0"></a><br><font face="Arial,Helvetica,Geneva,Swiss,SunSans-Regular" align="center" size=32>Qtopia</font>   <a href="index.html">Home</a> - <a href="qtopiaclasses.html">Classes</a> - <a href="qtopiaannotated.html">Annotated</a> - <a href="qtopiafunctions.html">Functions</a> - <a href="qtindex.html">Qt Embedded</a></td><td align="right" valign="top">  <table border="0" cellpadding="0" cellspacing="0" width="137">  <tr>  <td><a href="http://www.trolltech.com/company/about/trolls.html"><img height="100" width="100" src="face.png" border="0"></a></td>  <td><img height="100" width="100" src="qtlogo.png" align="top" border="0"></td>  </tr>  </table></td></tr></table><h1 align=center>Qtopia Plugins</h1><p> <p> Contents<!-- toc --><ul><li><a href="#1"> Introduction</a><li><a href="#2"> Writing the functionality</a><li><a href="#3"> Subclassing the interface</a><li><a href="#4"> Implementing the interface</a><li><a href="#5"> Creating an instance</a><li><a href="#6"> Loading Plugins</a></ul><!-- endtoc --><p> <h2> Introduction</h2><a name="1"></a><p> Plugins are implemented in Qtopia via a COM-like layer.  The basic stepsto writing any Qtopia plugin are:<ul><li> Write the functionality that the plugin will provide.<li> Subclass the interface for the plugin you wish to write.<li> Provide implemetations for the interface methods.<li> Create an instance of the plugin.</ul><p> There are also some basic rules to follow when writing a plugin:<ul><li> Due to the implementation details of moc, it is important that any QObjectsubclasses in your plugin have unique names to prevent clashes betweentwo plugins.  As a rule, use a unique prefix for all classes includinginternal classes.  For example, if a plugin "foo" has an internal helperclass that is a QObject subclass, it should be named FooHelperrather than Helper.<li> Plugins should not leak memory.  Since a plugin may be unloaded at anytime it is important to cleanup all used memory when your plugin interfaceis destructed.</ul><p> <h2> Writing the functionality</h2><a name="2"></a><p> Consider the following fictious plugin interface:<p> <pre>// {05E0A4AB-DDC5-4449-85A9-828100DE00A9} #ifndef IID_WidgetPlugin#define IID_WidgetPlugin QUuid( 0x05e0a4ab, 0xddc5, 0x4449, 0x85, 0xa9, 0x82, 0x81, 0x00, 0xde, 0x00, 0xa9)#endifstruct WidgetPluginInterface : public QUnknownInterface{    virtual QWidget *widget( QWidget *parent ) = 0;    virtual QString name() const = 0;};</pre> <p> This is a simple interface that provides a plugin name and a widget thatis created with the supplied parent.<p> IID_WidgetPlugin defines a unique ID for this interface.<p> The plugin that we are writing provides a widget that draws an ellipse inits center.  The code below implements the functionality that this pluginprovides.<p> <pre>class EllipseWidget : public QWidget{    Q_OBJECTpublic:    EllipseWidget( QWidget *parent=0 ) : QWidget( parent, "Ellipse" )    {    }protected:    void paintEvent( QPaintEvent * )    {        QPainter p( this );        p.drawEllipse( rect() );    }};</pre> <p> <h2> Subclassing the interface</h2><a name="3"></a><p> Now you can subclass the WidgetPluginInterface:<p> <pre>struct CirclePlugin : public WidgetPluginInterface{public:    virtual QWidget *widget( QWidget *parent );    virtual QString name() const;    QRESULT queryInterface( const <a href="quuid.html">QUuid</a>&amp;, QUnknownInterface** );    Q_REFCOUNTprotected:    CircleWidget *w;    ulong ref;};</pre> <p> There are two things to note in the CirclePlugin struct:<ul><li> the queryInterface() function allows the plugin loader to querywhat interfaces the plugin implements.<li> Q_REFCOUNT is a macro to simplify the reference counting.This macro expects the ulog ref variable to be present.</ul><p> <h2> Implementing the interface</h2><a name="4"></a><p> The constructor an destructor are straight-forward.  The most importantpoint is that ref must be initialised with 0.<pre>CirclePlugin::CirclePlugin()    : w(0), ref(0){}CirclePlugin::~CirclePlugin(){    delete w;}</pre> <p> The queryInterface() function can be implemented using thefollowing boilerplate code:<p> <pre>QRESULT CirclePlugin::queryInterface( const <a href="quuid.html">QUuid</a> &amp;uuid, QUnknownInterface **iface ){    *iface = 0;    if ( uuid == IID_QUnknown )        *iface = this;    else if ( uuid == IID_WidgetPlugin )        *iface = this;    else        return QS_FALSE;    (*iface)-&gt;addRef();    return QS_OK;}</pre> <p> A plugin can provide several interfaces.  At the very least QUnknownInterfaceis provided by all plugins.<p> The widget() function returns the widget.<p> <pre>QWidget *CirclePlugin::widget( QWidget *parent ){    if ( !w )        w = new CircleWidget( parent );    return w;}</pre> <p> The name() function returns the name of the plugin.<p> <pre>QString CirclePlugin::name(){    return qApp-&gt;translate( "WidgetPlugin", "Circle" );}</pre> <p> <h2> Creating an instance</h2><a name="5"></a><p> You must also create an instance of the widget plugin using thefollowing boilerplate code:<p> <pre>Q_EXPORT_INTERFACE(){    Q_CREATE_INSTANCE( CirclePlugin )}</pre> <p> <h2> Loading Plugins</h2><a name="6"></a><p> The recommended method for loading plugins is to use the <a href="pluginloader.html">PluginLoader</a> class.The PluginLoader class provides simplified enumeration and loading ofplugins and provides safety in cases where the system has been booted inSafe Mode.<p> <pre>PluginLoader loader( "Widgets" );QStringList list = pluginLoader.list();QStringList::Iterator it;QValueList&lt;WidgetPluginInterface*&gt; widgetsList;for ( it = list.begin(); it != list.end(); ++it ) {    WidgetPluginInterface *iface = 0;    if ( pluginLoader.queryInterface( *it, IID_WidgetPlugin, (QUnknownInterface**)&amp;iface ) == QS_OK &amp;&amp; iface ) {        widgetsList.append( iface );    }}</pre> <p> The PluginLoader class expects the plugins to be installed in the$QPEDIR/plugins/<i>type</i> directory.<p> <!-- eof --><p><address><hr><div align="center"><table width="100%" cellspacing="0" border="0"><tr><td>Copyright &copy; 2001-2004 Trolltech<td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a><td align="right"><div align="right">Qtopia version 2.0.0</div></table></div></address></body></html>
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