CHAPTER 4. DEVELOPING APPLICATIONS

4.9 PLUG-IN

A. An overview of Plug-in structure

MzLibLoader was created to support plug-in function in MIZI Prizm 2.0.
This section explains not only HOW-TO use the class but also explains HOW-TO design plug-in.

The Plug-in consists of following three units;

Body: This is a part which implements functionalities of your plug-in.
Factory (class MzLibFactory): A plug-in contains multiple bodies which are controlled by factory. Loader will provide information regarding to factory, and then factory can create body. You need to create a factory which runs with plug-in well.
Loader (class MzLibLoader): Loader conducts two functionalities. It loads target plug-in file, and then manages loaded plug-in. Loader can't detect body information therefore it simply manages factory.

B. Plug-in Body Example

Next is a sample code that a body acts like QWidget for displaying time.

#include <stdio.h> 
#include <qlabel.h> 
#include <qdatetime.h> 
#include <mzlibloader.h> 
 
class TimeApplet : public QLabel 
{ 
public: 
    TimeApplet (QWidget *parent); 
 
protected: 
    virtual void timerEvent (QTimerEvent *); 
}; 
 
 
TimeApplet::TimeApplet (QWidget *parent) 
        : QLabel (parent) 
{ 
    timerEvent (NULL); 
    startTimer (30 * 100); 
} 
 
 
void TimeApplet::timerEvent (QTimerEvent *e) 
{ 
    QTime time = QTime::currentTime (); 
    QString text; 
 
    text.sprintf ("%d:%02d", time.hour (), time.minute ()); 
    setText (text); 
}

C. Plug-in Factory Example

Following sample was written to make plug-in. TimeApplet in the sample can be worked as an actual plug-in.

class AppletFactory : public MzLibFactory 
{ 
public: 
    AppletFactory (); 
 
    virtual QString description () const; 
    virtual QString version () const; 
 
protected: 
    virtual QObject* createObject (QObject* parent, const char* name, 
                                   const char* classname, 
                                   const QStringList &args); 
}; 
 
 
AppletFactory::AppletFactory () 
{ 
 // Constructor 
} 
 
QString AppletFactory::description () const 
{ 
    return QString ("Time Applet"); 
} 
 
QString AppletFactory::version () const 
{ 
    return QString ("1.0"); 
} 
  
QObject* AppletFactory::createObject (QObject* parent, const char* name, 
                                      const char* classname, 
                                      const QStringList &) 
{ 
    if (!strcmp (classname, "QWidget")) { 
        if (parent && !parent->isWidgetType ()) 
            return 0; 
 
        return new TimeApplet ((QWidget *) parent); 
    } 
 
    return 0; 
} 
 
// MACRO for plug-in registration 
MZ_EXPORT_FACTORY (AppletFactory);

D. Plug-in Compile

Create a file, "time.cpp", which combines Body and Factory.

Create Makefile.am as follow, then compiles.

CXXLD = @CC@ 
INCLUDES = -I.. @LINUETTE_COMMON_INCLUDE@ -Wall 
 
interfaces_LTLIBRARIES =    \ 
 libtime.la 
 
interfacesdir = @LINUETTE_PLUG-IN_DIR@ 
 
libtime_la_SOURCES =   \ 
 time.cpp 
 
libtime_la_LDFLAGS =   \ 
        -export-dynamic   \ 
 -avoid-version

E. Load Plug-in

Now, let's load the above plug-in.

#include <mzlibloader.h> 
 
class Plug-inViewer : public QWidget 
{ 
public: 
 Plug-inViewer (); 
}; 
 
void Plug-inViewer::Plug-inViewer () 
{ 
 // Load "libtime.so" file. If fail then return NULL. 
 MzLibFactory *factory = MzLibLoader::instance ()->load (¡°libtime.so¡±); 
 if (factory) { // plug-in loaded 
  // display about the factory
  qDebug ("Factory Info: %s (version %s)" ,  
    factory->description ().latin1 (), factory->version ().latin1 ()); 
  // Create a widget through plug-in factory. 
  QWidget *w = (QWidget *) factory->create (this, ¡°time¡±, ¡°QWidget¡±); 
  w->show (); 
 } 
}

See function factory->create () original code.

QObject * MzLibFactory::create (QObject *parent = 0, const char *name = 0, 
    const char *classname = "QObject", 
    const QstringList &args = QstringList ());

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MIZI Prizm 2.0.0