Why do I not get any MouseEvents in a QGraphicsItem derived class?

Niagarer

Hey,
I have a QGraphicsView, which displays a QGraphicsScene in a tabWindget.
In this scene I can add QGraphicsItems by clicking on it (class called Node).
I want to receive mouseEvents in my QGraphicsItem derived class. I already found this solution: Just writing

QGraphicsView::mousePressEvent(event);

to the end of mousePressEvent-function in my QGraphicsView.
Unfortunately it doesn't work. I receive no mousePressEvent in my Node class.
My mousePressEvent in the QGraphicsView derived class:

void GraphWidget::mousePressEvent(QMouseEvent *event){

    if (event->button() == Qt::RightButton) // doesn't matter I think
    {
        rightMousePressed = true;
        _panStartX = event->x();
        _panStartY = event->y();
        setCursor(Qt::ClosedHandCursor);
        event->accept();
        return;
    }
    QGraphicsView::mousePressEvent(event);
}

I also tried to get the selected Node this way (in the QGraphicsView class also in the MousePressEvent-func):

    Node *myNode = static_cast<Node*>(itemAt(event->pos()));
    qDebug() << "selected node: " << myNode;
    myNode->speak(); // speak() is a funtion in my Node class
    setSelectedNode(myNode);

and this way (also in the QGraphicsView class also in the MousePressEvent-func) :

    for(Node* i : all_nodes){
        if(i->isSelected()){
            setSelectedNode(i); // selectedNode is a Node* attribute of my QGraphicsView class
            i->speak();
            break;
        }
    }

Both ways don't work. The program just crashes when I click to the scene.
This is the constructor of my QGraphicsItem derived class:

Node::Node(GraphWidget *graphWidgetInput)
{
    setFlag(ItemIsMovable);
    setFlag( ItemIsSelectable, true );
    setFlag(ItemSendsGeometryChanges);
    setCacheMode(DeviceCoordinateCache);
    setZValue(-1);
    graph = graphWidgetInput;
    width = 100;
    height = 100;
}

Any ideas what I missed?
Thanks for answers

Niagarer

The final answer for all these problems is there:
https://forum.qt.io/topic/82085/qgraphicsview-mousereleaseevent-ensures-that-i-can-t-select-qgraphicsitems-anymore/2

? Offline

Hi! The following works with Qt 5.9. It prints "Item" if you click on a custom item, and it prints "Nothing" if you click on empty space in the custom view.

myview.h

#ifndef MYVIEW_H
#define MYVIEW_H

#include <QGraphicsView>

class MyView : public QGraphicsView
{
public:
    MyView(QWidget *parent = Q_NULLPTR);
protected:
    virtual void mousePressEvent(QMouseEvent *event) override;
};

#endif // MYVIEW_H

myview.cpp

#include "myview.h"
#include <QMouseEvent>
#include <QGraphicsItem>
#include <QDebug>

MyView::MyView(QWidget *parent)
    : QGraphicsView(parent)
{
}

void MyView::mousePressEvent(QMouseEvent *event)
{
    if (!itemAt(event->pos())) {
        qDebug("Nothing");
    }
    QGraphicsView::mousePressEvent(event);
}

myitem.h

#ifndef MYITEM_H
#define MYITEM_H

#include <QGraphicsItem>

class MyItem : public QGraphicsItem
{
public:
    MyItem(QGraphicsItem *parent = Q_NULLPTR);
    virtual QRectF boundingRect() const override;
    virtual void paint(QPainter *painter, QStyleOptionGraphicsItem const *, QWidget *) override;
protected:
    virtual void mousePressEvent(QGraphicsSceneMouseEvent *) override;
};

#endif // MYITEM_H

myitem.cpp

#include "myitem.h"
#include <QPainter>
#include <QDebug>

MyItem::MyItem(QGraphicsItem *parent)
    : QGraphicsItem(parent)
{
}

QRectF MyItem::boundingRect() const
{
    auto const penWidth = 1.0;
    return QRectF(-10 - penWidth / 2, -10 - penWidth / 2, 20 + penWidth, 20 + penWidth);
}

void MyItem::paint(QPainter *painter, QStyleOptionGraphicsItem const *, QWidget *)
{
    painter->setBrush(QBrush(QColor("orange")));
    painter->setPen(QColor("lime"));
    painter->drawRect(-10, -10, 20, 20);
}

void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *)
{
    qDebug() << "Item";
}

Niagarer

@Wieland
Ok, thank you!
I tried it in my project, it didn't work in version 5.8 so I downloaded 5.9.1 and now I'm unfortunately having problems with the Qt version. It says, this is Qt version 5.9.1 for Android (?) and it can't build and run my project. I downloaded and installed the normal version, not for Android... Phew I don't know, I will look and update when I have it (I hate it when I can't continue a project because of such unnessecary problems -.- )

? Offline

I'm sorry to hear that :-/ But I'm sure it works with 5.8, too. I only mentioned 5.9 because I thought you might be using 4.7 or older.

Niagarer

This post is deleted!

Niagarer

@Wieland
Ok, I reinstalled it and added the things I needed (I hope) and made a new project with your code (and some additional lines) and it worked. But my big project still does not work and so far, I cant find the mistake. However I tried to do the procedure nearly the same as in your example, it does not work yet

Niagarer

This post is deleted!

Niagarer

This post is deleted!

Niagarer

This post is deleted!

Niagarer

This post is deleted!

Niagarer

The final answer for all these problems is there:
https://forum.qt.io/topic/82085/qgraphicsview-mousereleaseevent-ensures-that-i-can-t-select-qgraphicsitems-anymore/2