Why does mousePressEvent to QGraphicsItem bugs out after opening a QDialog with exec or open? - qt

Question

I wrote a minimal working example of the problem and I believe it might be a Qt bug. But just in case I wanted to ask.
Here are My classes:
mydialog.h
#include <QDialog>
#include <QVBoxLayout>
#include <QLabel>
class MyDialog : public QDialog
{
public:
MyDialog(QWidget *parent = 0);
};
mydialog.cpp
#include "mydialog.h"
MyDialog::MyDialog(QWidget *parent):QDialog(parent)
{
QLabel *label = new QLabel("Some random dialog",this);
QVBoxLayout *layout = new QVBoxLayout();
layout->addWidget(label);
this->setLayout(layout);
}
myitem.h
#include <QGraphicsTextItem>
#include <QPainter>
#include <QDebug>
#include "mydialog.h"
class MyItem : public QGraphicsItem
{
public:
MyItem();
void paint(QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0);
QRectF boundingRect() const {return boundingBox;}
void setMyDialog(MyDialog *d){ dialog = d; }
private:
QRectF boundingBox;
MyDialog *dialog;
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *e);
};
myitem.cpp
MyItem::MyItem()
{
boundingBox = QRectF(0,0,200,100);
}
void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){
painter->setBrush(QBrush(Qt::red));
painter->drawRect(boundingBox);
}
void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *e){
//dialog->exec(); // BUG
//dialog->open(); // BUG
dialog->show(); // WORKS!
}
test.h
#include "myitem.h"
namespace Ui {
class Test;
}
class Test : public QMainWindow
{
Q_OBJECT
public:
explicit Test(QWidget *parent = 0);
~Test();
protected:
void resizeEvent(QResizeEvent *e);
private:
Ui::Test *ui;
MyDialog *diag;
};
And test.cpp
Test::Test(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::Test)
{
ui->setupUi(this);
ui->graphicsView->setScene(new QGraphicsScene(this));
diag = new MyDialog(this);
}
void Test::resizeEvent(QResizeEvent *e){
ui->graphicsView->setSceneRect(0,0,ui->graphicsView->width(),ui->graphicsView->height());
ui->graphicsView->scene()->clear();
MyItem *item = new MyItem();
item->setMyDialog(diag);
ui->graphicsView->scene()->addItem(item);
}
Test::~Test()
{
delete ui;
}
So here is what happens (tested on Qt 5.7 and Qt 5.6). If the dialog is opened with either exec or open then, after it is closed ALL further mouse clicks ANYWHERE on the screen will open up the dialog again, making it impossible to interact with anything else drawn in there. This happens ONLY after it is opened for the first time. If i resize the screen, the item is recreated and I can click normally again. If I again click on the red box, then again all further clicks anywhere on the screen open up the dialog
However if the Dialog is opened by show, then it works as expected, only showing again if I click on the red rectangle.
Now the obvious problem is that exec make the dialog block execution until it is closed, but show doesn't. I can program around this using signals, but my question is why? and Is this a bug?

Answer 1

It seems that MyItem's reimplementation of mousePressEvent needs some behavior provided by default implementation. Here is the code, works fine in my machine:
void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *event){
dialog->exec(); // WORKS
//dialog->open(); // WORKS
//dialog->show(); // WORKS
QGraphicsItem::mousePressEvent(event);
}