QGraphicsview mouserelease event does not register - qt

Question

I am trying to get the scene coordinates of a both a mousepress and a mouserelease event by means of an event filter.
It works fine for the mousepress, but the mouserelease seems not to be registering.
What am I missing here?
Please note I am using Qt Creator 2.2.0(based on Qt 4.7.4)
class mouseEater : public QObject{
// Q_OBJECT
protected:
bool eventFilter(QObject *obj, QEvent *event);
};
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
mouseEater *eater = new mouseEater();
QGraphicsScene *scene;
scene = new QGraphicsScene();
ui->view->installEventFilter(eater);
ui->view->setScene(scene);
}
bool mouseEater::eventFilter(QObject *obj, QEvent *event){
QMouseEvent *mEvent = static_cast<QMouseEvent *>(event);
QPoint point = mEvent->pos();
cout<<"type:"<<event->type()<<endl;
switch(event->type()){
case QEvent::MouseButtonPress:
cout<<"mousepress at "<<point.x()<<","<<point.y()<<endl;
return true;
break;
case QEvent::MouseButtonRelease:
cout<<"mouserelease at "<<point.x()<<","<<point.y()<<endl;
return true;
break;
default:
//standard event processing
return QObject::eventFilter(obj, event);
break;
}
return 0;
}

Answer 1

The quick answer is that QGraphicsView doesn't seem to allow other QObjects to eat its mouseReleaseEvents. I'm not sure why just yet, but I think it's something to do with how mouseReleaseEvent() is reimplemented in QGraphicsView. A little hacking gives a workaround though:
HEADER:
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
protected:
virtual bool eventFilter(QObject *, QEvent *);
private:
Ui::MainWindow *ui;
};
class cDerived : public QGraphicsView
{
Q_OBJECT
public:
cDerived(QWidget *parent) : QGraphicsView(parent) {}
protected:
virtual void mousePressEvent(QMouseEvent *event);
virtual void mouseReleaseEvent(QMouseEvent *event);
};
SOURCE:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QGraphicsView *View = new cDerived(ui->centralWidget);
QGraphicsScene *Scene = new QGraphicsScene(ui->centralWidget->rect(), ui->centralWidget);
View->setScene(Scene);
View->installEventFilter(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
switch(event->type())
{
case QEvent::MouseButtonPress:
qDebug()<<"eaten mousepress";
return true;
break;
case QEvent::MouseButtonRelease:
qDebug()<<"eaten mouserelease";
return true;
break;
default:
//standard event processing
return QObject::eventFilter(obj, event);
break;
}
}
void cDerived::mousePressEvent(QMouseEvent *event)
{
qDebug()<<"mousepress";
event->ignore();
}
void cDerived::mouseReleaseEvent(QMouseEvent *event)
{
qDebug()<<"mouserelease";
event->ignore();
}
Try commenting out the 'event->ignore()' calls in the reimplemented mouse event catchers and it becomes clear how the mouseReleaseEvent() in QGraphicsView might be going wrong...
If you can reimplement QGraphicsView as a very thin class with just the constructor and mouseReleaseEvent() { event->ignore() } then you should be able to get around this bug (though, while this hack seems to be stable - suggesting that your problem might be a bug in QGraphicsView, without exhaustively looking through the QGraphicsView source we can't be sure this isn't in fact an intended feature and therefore that this hack won't break anything down the line!)
-Sam

Answer 2

Use QGraphicsSceneMouseEvent and the likes instead of QMouseEvent. As I found out in my question, QGraphicsScene does not dispatch normal mouse events.
Best regards