This simple app calculates the width of a QGraphicsView and displays it in a statusbar and updates the value every time the size changes. Check against your own code to see what's wrong.

Qt Code: 
  1. #include <QApplication>
  2. #include <QtGui>
  3.  
  4. class MainWindow : public QMainWindow
  5. {
  6.         Q_OBJECT
  7.         public:
  8.                 MainWindow(QWidget* parent=0) : QMainWindow(parent) {
  9.                         view = new QGraphicsView;
  10.                         view->installEventFilter(this);
  11.                         setCentralWidget(view);
  12.  
  13.                 }
  14.                 bool eventFilter(QObject* obj, QEvent* event) {
  15.                         if (obj == view && event->type() == QEvent::Resize)
  16.                                 statusBar()->showMessage(QString::number(view->width()));
  17.                         return QMainWindow::eventFilter(obj, event);
  18.                 }
  19.         private:
  21.  
  22.  
  23. };
  24.  
  25. #include "main.moc"
  26. int main(int argc, char* argv[])
  27. {
  28.         QApplication app(argc, argv);
  29.         MainWindow mw;
  30.         mw.show();
  31.         return app.exec();
  32. }
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