Qt access variable from custom object from QGridLayout - c++

Question

I have created my own QGraphicsView so I can use the mousePressEvent method. I then add the "new" widget to the MainWindow. Now I need to access a scene from that object, but I have trouble accessing it.
privqgraphicsview.cpp
#include "privqgraphicsview.h"
#include <QPointF>
MyQGraphicsView::MyQGraphicsView(QWidget *parent) :
QGraphicsView(parent)
{
scene = new QGraphicsScene();
this->setSceneRect(-320, -290, 660, 580);
this->setScene(scene);
this->setRenderHint(QPainter::Antialiasing);
}
privqgraphicsview.h
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsEllipseItem>
#include <QMouseEvent>
class MyQGraphicsView : public QGraphicsView
{
Q_OBJECT
public:
explicit MyQGraphicsView(QWidget *parent = 0);
QGraphicsScene * scene;
public slots:
void mousePressEvent(QMouseEvent * e);
};
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "privqgraphicsview.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
// gridLayout is defined in mainwindow.h
gridLayout = new QGridLayout(ui->centralWidget);
gridLayout->addWidget( new MyQGraphicsView() );
}
MainWindow::~MainWindow()
{
delete ui;
}
Now, I have the button in MainWindow on which click event I would like to connect points which are in MyQGraphicsView's scene from gridLayout. I have tried something like this:
void MainWindow::on_connectPointsPB_clicked()
{
QLayoutItem *myView = gridLayout->itemAt(0);
// trying to draw a simple line, code below does not check anything, I am aware of it
dynamic_cast<MyQGraphicsView *>(myView)->scene->addLine(10,10,50,50, QPen(Qt::red, 3));
}
And that does shutdown (crash) the app after the button is clicked.

Answer 1

You should not cast QLayoutItem, but QLayoutItem::widget to your MyQGraphicsView. If you checked the outcome of dynamic_cast<MyQGraphicsView *>(myView), you would have noticed that it returns NULL. Note that it may be useful to use qobject_cast instead of dynamic_cast, which does not require RTTI support.
A cleaner solution would be to store your MyQGraphicsView object as a member of MainWindow, so you do not need to cast anything.