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

? 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