[Qgis-user] problem in plugin writing

[Bijay Panda]

Hi All,
I am new to QGIS.I am writing a plugin to simply draw a simple stuff in
mapCanvas in ubuntu linux.
I already created a plugin toolButton .I want to draw a triangle or
rectangle when my pluging will be selected.
I followed following process.
1)create a toolBarIcon in initGui()
2)took a slot to render the drawig stuffs.
3)inside that slot i called Qpainter to paint something.
4)connect that slot inside initGui() to mapCanvas.

5)I am loading lib libraries into plugin folder(/usr/lib/qgis)

#include "qgspointconverterplugin.h"

#ifdef WIN32
#define QGISEXTERN extern "C" __declspec( dllexport )
#else
#define QGISEXTERN extern "C"
#endif
QgsPointConverterPlugin::QgsPointConverterPlugin(QgisInterface* iface):
mIface(iface), qGisInterface( iface)
{
}
QgsPointConverterPlugin::~QgsPointConverterPlugin()
{
}
void QgsPointConverterPlugin::initGui()
{
  // myQActionPointer = new QAction( QIcon( ":/scale_bar.png" ), tr( "&Scale
Bar" ), this );
  mAction = new QAction(tr("&Convert to point"), this);
  connect(mAction, SIGNAL(activated()), this, SLOT( run() ) );
  connect( qGisInterface->mapCanvas(), SIGNAL( renderComplete( QPainter * )
), this, SLOT( render(QPainter * )) );

  mIface->addToolBarIcon(mAction);
  mIface->addPluginToMenu(tr("&Convert to point"), mAction);
}
void QgsPointConverterPlugin::unload()
{
  mIface->removeToolBarIcon(mAction);
  mIface->removePluginMenu(tr("&Convert to point"), mAction);
  delete mAction;
}
void QgsPointConverterPlugin::refreshCanvas()
{
  qGisInterface->mapCanvas()->refresh();
}
void QgsPointConverterPlugin::run()
{
  /*QgsScaleBarPluginGui *myPluginGui = new QgsScaleBarPluginGui(
qGisInterface->mainWindow(), QgisGui::ModalDialogFlags );
  myPluginGui->setAttribute( Qt::WA_DeleteOnClose );
  myPluginGui->setPreferredSize( mPreferredSize );
  myPluginGui->setSnapping( mSnapping );
  myPluginGui->setPlacementLabels( mPlacementLabels );
  myPluginGui->setPlacement( mPlacementIndex );
  myPluginGui->setEnabled( mEnabled );
  myPluginGui->setStyleLabels( mStyleLabels );
  myPluginGui->setStyle( mStyleIndex );
  myPluginGui->setColour( mColour );*/

  /*connect( myPluginGui, SIGNAL( changePreferredSize( int ) ), this, SLOT(
setPreferredSize( int ) ) );
  connect( myPluginGui, SIGNAL( changeSnapping( bool ) ), this, SLOT(
setSnapping( bool ) ) );
  connect( myPluginGui, SIGNAL( changePlacement( int ) ), this, SLOT(
setPlacement( int ) ) );
  connect( myPluginGui, SIGNAL( changeEnabled( bool ) ), this, SLOT(
setEnabled( bool ) ) );
  connect( myPluginGui, SIGNAL( changeStyle( int ) ), this, SLOT( setStyle(
int ) ) );
  connect( myPluginGui, SIGNAL( changeColour( QColor ) ), this, SLOT(
setColour( QColor ) ) );
  connect( myPluginGui, SIGNAL( refreshCanvas() ), this, SLOT(
refreshCanvas() ) );
  myPluginGui->show();*/
}
void QgsPointConverterPlugin::render(QPainter *painter)//
{

  qWarning("in method convertToPoint");
  QPen myForegroundPen( mColour, 2 );
  QPen myBackgroundPen( Qt::white, 4 );
  QPolygon polygon( 4 );
  painter->setPen( myBackgroundPen );
  polygon.putPoints( 0,
4,10,20,30,40,50,60);
  painter->drawPolyline( polygon );
  //QPainter *painter;
/*  QPainter paint( this );
  paint.setPen( Qt::blue );
  paint.drawRect(20,30,40,45 );*/

  /*QPolygon pa( 4 );
  pa.setPoint( 0, 10, 10 );
  pa.setPoint( 1, 20, 10);
  pa.setPoint( 2, 20, 20 );
  pa.setPoint( 3, 10,20 );
  painter->drawPolygon( pa );*/
}

QGISEXTERN QgisPlugin* classFactory(QgisInterface* iface)
{
  return new QgsPointConverterPlugin(iface);
}

QGISEXTERN QString name()
{
  return "point converter plugin";
}
QGISEXTERN QString description()
{
  return "A plugin that converts vector layers to delimited text point
files";
}
QGISEXTERN QString version()
{
  return "0.00001";
}


// Return the type (either UI or MapLayer plugin)
QGISEXTERN int type()
{
  return QgisPlugin::UI;
}
// Delete ourself
QGISEXTERN void unload(QgisPlugin* theQgsPointConverterPluginPointer)
{

  //disconnect( qGisInterface->mapCanvas(), SIGNAL( renderComplete( QPainter
* ) ),
              //this, SLOT( renderScaleBar( QPainter * ) ) );
 // refreshCanvas();

  //delete myQActionPointer;
  delete theQgsPointConverterPluginPointer;
}

But it's not drawing anything,rather application crashes when i load my
plugin.
can any one plz help me out.
-- 
Thanks & Regards
Bijay
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