[SOLVED] Detecting mouse click in scene (QGraphicsScene) help

Demmy

I'm attempting to get to know some QGraphicsScene options and it's going tough on me.

What I'm trying to do: When I click on scene, I want a rectangle to be shown/hidden (toggle).

What I've managed to do so far: If I use QMouseEvent instead of QGraphicsMouseEvent it works well, with the exception of it being toggled even if I click outside the scene. If I use QGraphicsMouseEvent it does not trigger.

pomocnidrugi.cpp
@#include "pomocnidrugi.h"
#include "ui_pomocnidrugi.h"
#include "QGraphicsItem.h"

bool jePressed=false;
pomocnidrugi::pomocnidrugi(QWidget *parent) :
QWidget(parent),
ui(new Ui::pomocnidrugi)
{
ui->setupUi(this);

scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
ui->graphicsView->setRenderHint(QPainter::Antialiasing);

QBrush redBrush(Qt::red);
QBrush blueBrush(Qt::blue);
QPen blackPen(Qt::black);
blackPen.setWidth(6);

ellipse = scene->addEllipse(10,10,100,100,blackPen, redBrush);
rectangle = scene ->addRect(10,210,100,310,blackPen,blueBrush);
rectangle->setFlag(QGraphicsItem::ItemIsMovable);

}

pomocnidrugi::~pomocnidrugi()
{
delete ui;
}
void pomocnidrugi::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
if(jePressed){rectangle->show(); jePressed=false;}
else{rectangle->hide(); jePressed=true;}
}
@

pomocnidrugi.h
@#ifndef POMOCNIDRUGI_H
#define POMOCNIDRUGI_H

#include <QWidget>
#include <QGraphicsScene>

namespace Ui {
class pomocnidrugi;
}

class pomocnidrugi : public QWidget
{
Q_OBJECT

public:
explicit pomocnidrugi(QWidget *parent = 0);
~pomocnidrugi();

private:
Ui::pomocnidrugi *ui;
QGraphicsScene *scene;
QGraphicsEllipseItem *ellipse;
QGraphicsRectItem *rectangle;
//QTimer *timer;

protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event);

};

#endif // POMOCNIDRUGI_H@

This is ofcourse non-working state (again, it does trigger if I use QMouseEvent instead of QGraphicsSceneMouseEvent - but not completely as intended).

What am I supposed to do to make it work? I would appriciate the easiset solution possible, I'm still in the early phase of learning.

jeremy_k

Is the goal to detect a click anywhere within the [view of the] scene, or within an individual item in the scene?

Within the context of a scene displayed by a view, QGraphicsSceneMouseEvents are delivered to items within the scene and the scene itself. QMouseEvents are delivered to the view.

Demmy

[quote author="jeremy_k" date="1402970867"]Is the goal to detect a click anywhere within the [view of the] scene, or within an individual item in the scene?

Within the context of a scene displayed by a view, QGraphicsSceneMouseEvents are delivered to items within the scene and the scene itself. QMouseEvents are delivered to the view.[/quote]

The goal is anywhere within a scene (or graphicsView box). What do you propose I do? QMouseEvent delivered but it triggered even outside the scene/graphicsView (as long as it's in that window). QGraphicsSceneMouseEvent does not trigger at all, inside or outside the scene.

JvdGlind

I am not entirely sure, but you are implementing mousePressEvent(QGraphicsSceneMouseEvent *event); in QWidget, not in QGraphicsScene. QWidget does not have a virtual function for QGraphicsSceneMouseEvent, but does have one for QMouseEvent, so my guess is that is why it is called only for the latter.

Demmy

[quote author="JvdGlind" date="1403015680"]I am not entirely sure, but you are implementing mousePressEvent(QGraphicsSceneMouseEvent *event); in QWidget, not in QGraphicsScene. QWidget does not have a virtual function for QGraphicsSceneMouseEvent, but does have one for QMouseEvent, so my guess is that is why it is called only for the latter.[/quote]

Thanks, I thought it would be because of that. However, how should I pull it out at this point? I tried another example with creating a separate class and header for a scene the way you desribed, which worked with QGraphicsSceneMouseEvent. Is there any workaround in this case?

jeremy_k

Another option is to install an event filter on the view. See "QObject::installEventFilter":http://qt-project.org/doc/qt-5/qobject.html#installEventFilterfor details.

There's also QGraphicsItem::installSceneEventFilter(), although it sounds like handling at the view level is more appropriate.

jerobarraco

thanks for the answer jeremy. thats cleaner than implementing a subclass of graphicsview just to trap an event

jerobarraco

thanks for the answer jeremy. thats cleaner than implementing a subclass of graphicsview just to trap an event