Create custom QT Widget

Define the main module that shows the widget

  1: #include <QtGui>
  2: #include "CustomWidget.h"
  3:  
  4: int main( int argc, char **argv )
  5: {
  6:   QApplication app( argc, argv );
  7:  
  8:   CustomWidget theCustomWidget;
  9:   CustomWidget.show();
 10:  
 11:   return app.exec();
 12: }

The custom widget header file  define a slot allows other modules to connect  in order to get mouse clicking events from the widget .

  1: #include <QtGui>
  2: #include <QWidget>
  3:  
  4: class CustomWidget : public QWidget
  5: {
  6:     Q_OBJECT
  7: public:
  8:    CustomWidget();
  9:  
 10: protected:
 11:     void paintEvent(QPaintEvent *event);
 12:   void mouseReleaseEvent ( QMouseEvent * e );
 13:     void mousePressEvent ( QMouseEvent * e );  
 14: private:
 15:   QPoint m_lastPoint;  
 16:     // member variable - flag of click beginning
 17:     bool mWasMouseClicking; 
 18:   
 19: signals:
 20:    void OnMouseClick(QPoint pPos);
 21: public slots:
 22: 
 23: private:
 24:   bool CheckIfPointInWidget (QPoint pPos);
 25:   int DistanceBetweenpoints (QPoint pFirstPt , QPoint pSecondPt);  
 26: };

The custom widget implementation cpp file.

  1: #include "CustomWidget.h"
  2:  
  3: void CustomWidget::paintEvent(QPaintEvent *event)
  4: {
  5:     //create a QPainter and pass a pointer to the device.
  6:     QPainter painter(this);
  7:  
  8:      painter.drawPolygon(polygon);
  9:  
 10:      //draw the widget for an example an ellipse
 11:      //Enables antialiasing, 
 12:    //set QPainter to use different
 13:      //color intensities on the edges to reduce the visual distortion that normally
 14:      //occurs when the edges of a shape are converted into pixels 
 15:      painter.setRenderHint(QPainter::Antialiasing, true);
 16:    
 17:    //Set the inner and the outer colors
 18:      painter.setPen(QPen(Qt::pink, 4, Qt::DashLine, Qt::RoundCap));
 19:      painter.setBrush(QBrush(Qt::blue, Qt::Dense5Pattern));
 20:      
 21:    painter.drawEllipse(200, 50, 250, 100);
 22:    }
 23:    
 24:    void CustomWidget::mousePressEvent ( QMouseEvent * e )
 25:   {
 26:     if ( CheckIfPointInWidget (e->pos()) == false )
 27:     {
 28:       return ;
 29:     }
 30:   
 31:     m_lastPoint = e->pos();
 32:     // set the flag meaning "click begin"
 33:     mWasMouseClicking = true;
 34:   }
 35:   void CustomWidget::mouseReleaseEvent ( QMouseEvent * e )
 36:   {
 37:     if (!mWasMouseClicking) )
 38:     {
 39:       return ;
 40:     }
 41:     
 42:     if ( CheckIfPointInWidget (e->pos()) == false )
 43:     {
 44:       mWasMouseClicking = false ;
 45:       return ;
 46:     }
 47:     
 48:     if ( Abs ( DistanceBetweenpoints (e->pos() , m_lastPoint) > 4 == true )
 49:     {
 50:       mWasMouseClicking = false ;
 51:       return ;
 52:     }  
 53:     emit OnMouseClick (e->pos());    
 54:   }

Sources:
http://www.youtube.com/watch?v=ScZn-cQiVFs&list=SP2D1942A4688E9D63
http://www.developer.nokia.com/Community/Wiki/MouseClick_event_in_Qt's_custom_widget
http://www.qtcentre.org/threads/19493-creating-custom-signa
http://harmattan-dev.nokia.com/docs/library/html/qt4/qbrush.html