QGraphicsObject: ContextMenu does not show up

sandro4912

I have a class derived from QGraphicsObject like this:

class Room : public QGraphicsObject
{
    Q_OBJECT
public:

//...
public:
    QRectF boundingRect() const override;

    void paint(QPainter *painter,
               const QStyleOptionGraphicsItem *option,
               QWidget *widget) override;

protected:
    void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override;

//....
}

painting ect works already. Just the contextMenu does not show up. I implemented it like this:

void Room::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QAction guessWumpusAction{tr("&Has Wumpus")};
    guessWumpusAction.setCheckable(true);
    connect(&guessWumpusAction, &QAction::triggered, this, &Room::guessWumpus);

    QAction guessBatAction{tr("&Has Bat")};
    if (mHasBat) {
        guessBatAction.setChecked(true);
        guessBatAction.setEnabled(false);
    }
    else {
        guessBatAction.setCheckable(true);
    }
    connect(&guessBatAction, &QAction::triggered, this, &Room::guessBat);

    QAction guessPitAction{tr("&Has Pit")};
    guessPitAction.setCheckable(true);
    connect(&guessPitAction, &QAction::triggered, this, &Room::guessPit);

    QMenu menu;
    menu.addAction(&guessWumpusAction);
    menu.addAction(&guessBatAction);
    menu.addAction(&guessPitAction);
    menu.popup(event->screenPos());

    qDebug() << event->screenPos();
}

I can see that the event is called on mouse right click on the widget as expected. However the context Menu does not pop up. Whats wrong here?

For test i call the class like this:

#include <QApplication>

#include "room.h"
#include <QGraphicsView>
#include <QGraphicsScene>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QGraphicsScene scene;
    QGraphicsView view;
    view.setScene(&scene);

    auto room = new Room;
    room->setVisible(true);
    scene.addItem(room);

    view.show();
    return QApplication::exec();
}

JonB

@sandro4912
Two guesses:
Are your co-ordinates right in menu.popup(event->screenPos()) (no mapping needed, I don't know)?
Your QMenu menu goes out of scope immediately after popup() (not exec())? You would need outside storage if you want to use popup(); test it with exec() instead? (I think it's this regardless of first point.)

sandro4912

I added exec and now it shows up. I could swear i saw an example with only popup. However now that it shows up it is only is triggered when I right click in the first 1/4 of the widget.(like if the widget has half the height and width.

I define boundingRect like this:

QRectF Room::boundingRect() const
{
    return QRectF{ QPointF{0, 0}, roomImage().size()};
}

were roomImage is a ressource:

QImage Room::roomImage() const
{
    return QImage{":/ressources/room.png"};
}

to paint i do this:

void Room::paint(
        QPainter *painter,
        const QStyleOptionGraphicsItem *option,
        QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)

    drawRoom(painter);
}

void Room::drawRoom(QPainter *painter)
{
    painter->drawImage(boundingRect(), roomImage());
}

JonB

@sandro4912
popup() can be used, but not with a stack variable QMenu like you had. Usually you'd new it.

For the area now: does ":/ressources/room.png" match how you spell resources on disk? Or you need to look at roomImage().size().

sandro4912

if i create menu dynamically who deallocates it later? I can't assign the Room to it as a parent since is not derrived from QWidget.

Also i tryed:

void Room::drawRoom(QPainter *painter)
{
    qDebug() << boundingRect();
    qDebug() << roomImage().size();

    painter->drawImage(boundingRect(), roomImage());
}

Which outputs:

QRectF(0,0 100x100)
QSize(100, 100)

So it should theoretically pop the menu in the whole image but it doesn't?

SGaist

Hi,

Make it a member variable and delete it in your class destructor.

JonB

@sandro4912
For dynamically created QMenu, then as @SGaist says.

But are you sure you need QMenu:popUp() and not just QMenu::exec() for your use case? It depends how you want it to work. If the simple exec() suffices you should be able to just use a stack (local) variable QMenu menu. You don't need the menu after it has returned the action the user clicked.

For your coordinates/click area, I don't think we're going to know. Is your image indeed 100x100 size, or is that maybe some default? Why don't you play with a bigger/smaller image and see what the pattern is?

sandro4912

there is nothing wrong with the image but to sort it out i did this:

void Room::paint(
        QPainter *painter,
        const QStyleOptionGraphicsItem *option,
        QWidget *widget)
{
    QRectF rect{boundingRect()};
    painter->setPen(Qt::black);
    painter->drawRect(rect);
}

QRectF Room::boundingRect() const
{
    return QRectF{ 0, 0, 200, 200};
}

Still the Menu is not popped up on the whole rect. It only appeas like on 1/3 of the size of QRectF{ 0, 0, 200, 200}; so is not always half. Does contextMenuEvent maybe check the size from somewhere else but not from the boundingRect ? Or is this simply a bug in QT?

I also compiled the code an a second OS to sort out that its not annother bug with KDE/Neon. But on Windows 10 same behaviour.

Also I stayed with the local Menu:

void Room::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    qDebug() << boundingRect();
    qDebug() << roomImage().size();

    QMenu menu;
    menu.addAction(mGuessWumpusAction);
    menu.addAction(mGuessBatAction);
    menu.addAction(mGuessPitAction);
    menu.exec(event->screenPos());
}

Any more ideas??

sandro4912

let me know if you need more information to find a solution for this issue. Maybe is even a qt bug.

Christian Ehrlicher

@sandro4912 said in QGraphicsObject: ContextMenu does not show up:

Still the Menu is not popped up on the whole rect. It only appeas like on 1/3 of the size of QRectF{ 0, 0, 200, 200}; so is not always half. Does contextMenuEvent maybe check the size from somewhere else but not from the boundingRect ?

I don't understand what you say here - does the popup / context menu event only works on 1/3 of your widget? Is the popup not as big as you expect?

sandro4912

the popup itself looks perfect.

The problem is it does not get triggered in the whole 200x200 area of the widget. It only looks like it gets shown in a smaller rectangle from the top left point.

so in 200x200 maybe only in 80x80 from top left point it gets created.

I would expect in the whole rectangle the context menu gets triggere.

maybe i should make a minimal running example so it can be verifyed.

Christian Ehrlicher

Ok, now it's clear to me. There are two examples (diagramscene, boxes) which work fine for me. Maybe you can try them out.

sandro4912

I made a minimal program and it works:

#ifndef RECTANGLE_H
#define RECTANGLE_H

#include <QGraphicsObject>

class Rectangle : public QGraphicsObject
{
    Q_OBJECT
public:
    explicit Rectangle(QGraphicsObject *parent = nullptr);

    QRectF boundingRect() const override;

    void paint(QPainter *painter,
               const QStyleOptionGraphicsItem *option,
               QWidget *widget) override;

protected:
    void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override;
};

#endif // RECTANGLE_H

#include "rectangle.h"

#include <QGraphicsSceneContextMenuEvent>
#include <QPainter>
#include <QMenu>

Rectangle::Rectangle(QGraphicsObject *parent)
    : QGraphicsObject(parent)
{
}

QRectF Rectangle::boundingRect() const
{
    return QRectF{ 0, 0, 100, 100};
}

void Rectangle::paint(
        QPainter *painter,
        const QStyleOptionGraphicsItem *option,
        QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)

    QRectF rect{boundingRect()};
    painter->setPen(Qt::black);
    painter->drawRect(rect);
}

void Rectangle::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QMenu menu;
    menu.addAction("Action 1");
    menu.addAction("Action 2");
    menu.exec(event->screenPos());
}

#include "rectangle.h"

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QGraphicsScene scene;

    Rectangle rectangle;
    scene.addItem(&rectangle);

    QGraphicsView view;
    view.setScene(&scene);

    view.show();
    return QApplication::exec();
}

Everything fine here the popup shows up in all the widget. The reason it does not work in my programm is. At some point i changed the class from QGraphicsObject to QGraphicsWidget. If we modify the minimal programm to have QGraphicsWidget as a base for Rectangle we get the Issue again:

#ifndef RECTANGLE_H
#define RECTANGLE_H

#include <QGraphicsWidget>

class Rectangle : public QGraphicsWidget
{
    Q_OBJECT
public:
    explicit Rectangle(QGraphicsWidget *parent = nullptr);

    QRectF boundingRect() const override;

    void paint(QPainter *painter,
               const QStyleOptionGraphicsItem *option,
               QWidget *widget) override;

protected:
    void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override;
};

#endif // RECTANGLE_H

#include "rectangle.h"

#include <QGraphicsSceneContextMenuEvent>
#include <QPainter>
#include <QMenu>

Rectangle::Rectangle(QGraphicsWidget *parent)
    : QGraphicsWidget(parent)
{
}

QRectF Rectangle::boundingRect() const
{
    return QRectF{ 0, 0, 100, 100};
}

void Rectangle::paint(
        QPainter *painter,
        const QStyleOptionGraphicsItem *option,
        QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)

    QRectF rect{boundingRect()};
    painter->setPen(Qt::black);
    painter->drawRect(rect);
}

void Rectangle::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{
    QMenu menu;
    menu.addAction("Action 1");
    menu.addAction("Action 2");
    menu.exec(event->screenPos());
}

#include "rectangle.h"

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QGraphicsScene scene;

    Rectangle rectangle;
    scene.addItem(&rectangle);

    QGraphicsView view;
    view.setScene(&scene);

    view.show();
    return QApplication::exec();
}

So why is the behaviour different with QGraphicWidget? How can it get fixed there?

Christian Ehrlicher

You forgot to set a proper size of the QGraphicsWidget: https://doc.qt.io/qt-5/qgraphicswidget.html#size-prop - since it's a widget you have to treat it like a widget which also means you have to set a proper size since there is no layout from where the size could be calculated from.

sandro4912

I solved the issue by resize in the constructor:

    resize(boundingRect().size());

That should be it or any other things to concern?

Christian Ehrlicher

@sandro4912 said in QGraphicsObject: ContextMenu does not show up:

That should be it or any other things to concern?

That's fine.