c++ - How to draw a Rectangle in Qgraphicsview dynamically (runtime), using Qt4 -

using qt creator version 2.4.1.

i'm starter on qt platform , trying draw rectangle dynamically. program uses 3 mouse events namely

• mousepressevent
• mousemoveevent
• mousereleaseevent

problems mousemoveevent never called.

here code snippet

main.cpp

#include <qtgui/qapplication> #include "dialog.h"  int main(int argc, char *argv[]) {     qapplication a(argc, argv);     dialog w;     w.show();      return a.exec(); } 

dialog.cpp

#include "dialog.h" #include "ui_dialog.h" #include "mysquare.h"  dialog::dialog(qwidget *parent) :     qdialog(parent),     ui(new ui::dialog) {     ui->setupui(this);     setmousetracking(true);     scene = new qgraphicsscene(this);     ui->graphicsview->setscene(scene);     scene->setbackgroundbrush(qt::black);     square = new mysquare;     scene->additem(square);     square->mpix = qpixmap(200,200);     square->mpix.fill(qt::white);     scene->addpixmap(square->mpix); }  dialog::~dialog() {     delete ui; }  void dialog::on_pushbutton_clicked() {     square->selectedtool = 1; } 

dialog.h

#ifndef dialog_h #define dialog_h  #include <qdialog> #include <qtcore> #include <qtgui> #include "mysquare.h"  namespace ui { class dialog; }  class dialog : public qdialog {     q_object  public:     explicit dialog(qwidget *parent = 0);     ~dialog();  private slots:     void on_pushbutton_clicked();  private:     ui::dialog *ui;     qgraphicsscene *scene;     mysquare *square;  };  #endif // dialog_h 

mysquare.cpp

#include "mysquare.h"  using namespace std;   mysquare::mysquare() {     pressed  = false;     selectedtool = 1;     mpix = qpixmap(200,200);     mpix.fill(qt::white); }  void mysquare::paint(qpainter *painter, const qstyleoptiongraphicsitem *option, qwidget *widget) {     painter->begin(this);     if(pressed)     {         painter->drawpixmap(0,0,mpix);         painter->drawrect(mrect);         drawstarted = true;     }     else if (drawstarted)     {         qpainter temppainter(&mpix);         temppainter.drawrect(mrect);         painter->drawpixmap(0,0,mpix);     }      painter->end(); }  void mysquare::mousepressevent(qgraphicsscenemouseevent *event) {     pressed = true;      y = event->pos();     cout<<"pos x : "<<y.x() <<endl;     cout<<"pos y : "<<y.y() <<endl;      if(selectedtool == 1)     {         mrect.settopleft(event->pos());         mrect.setbottomright(event->pos());          cout << "value of x_start axis " << x_1 <<endl;         cout << "value of y_start axis " << y_1 <<endl;     }     else if (selectedtool == 2)     {      }     update(); }  void mysquare::mousemoveevent(qgraphicsscenemouseevent *event) {     cout<<"inside mousemoveevent \n";     if(event->type() == qevent::mousemove)     {         if(selectedtool == 1){             mrect.setbottomright(event->pos());         }         else if (selectedtool == 2){             //mline.setp2(event->pos());         }     }     update(); }  void mysquare::mousereleaseevent(qgraphicsscenemouseevent *event) {     pressed = false;     update();     cout<<"inside mousereleaseevent \n"; } 

mysquare.h

#ifndef mysquare_h #define mysquare_h  #include <qpainter> #include <qgraphicsitem> #include <qdebug> #include <qpainter> #include <iostream> #include <qpixmap> #include <qpaintevent> #include <qgraphicsscenemouseevent>  class mysquare: public qgraphicsitem { public:     mysquare();     int selectedtool;     qpixmap mpix;     qrectf boundingrect() const;     void paint(qpainter *painter, const qstyleoptiongraphicsitem *option, qwidget *widget);     bool pressed;     bool drawstarted;  protected:     void mousepressevent(qgraphicsscenemouseevent *event);     void mousemoveevent(qgraphicsscenemouseevent *event);     void mousereleaseevent(qgraphicsscenemouseevent *event);  private:     qrectf mrect;     qpointf y;   private slots:  };  #endif // mysquare_h 

please guide me, thanks.

try setting property mousetracking true. you can read here

also have problems in code. example creating mysquare object using square = new mysquare;. can't see code call delete square.