QGraphicsScene + Mousevents general question

ademmler

Hi Pros,

do I always need to override Mouse events and build an Custom::Scene class if I want to get those on an QtGraphicsscene? I got this impression while googling for advice and trial code.

or ist there a simple way/slot to access an right mouse click on an QGraphicsScene?

Regards Alex

JonB

@ademmler said in QGraphicsScene + Mousevents general question:

or ist there a simple way/slot to access an right mouse click on an QGraphicsScene?

Do you mean by overriding QGraphicsScene::contextMenuEvent(QGraphicsSceneContextMenuEvent *contextMenuEvent) ?

ademmler

@JonB thx for response:

What I try to do is to react on an "right mouse click" within a QGraphicsViewScene.
For that Ihm looking fr the simplest solution ... I have some minimal example - but how can I upload here?

Regards Alex

ademmler

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);    
    ui->graphicsView->setEnabled(true);   
}

MainWindow::~MainWindow()
{
    delete ui;
}


void MainWindow::on_openButton_clicked()
{
    ui->statusbar->showMessage("Opening file ...", 0);

    QString imagePath = QFileDialog::getOpenFileName(
                this,
                tr("Open File"),
                QStandardPaths::writableLocation(QStandardPaths::DesktopLocation),
                tr("TIFF (*.tif *tiff);;JPEG (*.jpg *.jpeg);;PNG (*.png)" )
                );

    showImage(imagePath);
}

void MainWindow::showImage(QString imagePath)
{
    imageObject = new QImage();
    imageObject->load(imagePath);
    image = QPixmap::fromImage(*imageObject);

    scene = new QGraphicsScene(this);
    pixmap = scene->addPixmap(image);
    scene->setSceneRect(image.rect());
    ui->graphicsView->setScene(scene);

    pixmap->setFlag(QGraphicsItem::ItemIsMovable);
    ui->statusbar->showMessage("Idle.", 0);
}

void MainWindow::contextMenuEvent(QGraphicsSceneContextMenuEvent *contextMenuEvent)
{
    qDebug() << "QGS Event: " << contextMenuEvent << Qt::endl;
}

ademmler

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsPixmapItem>
#include <QFileDialog>
#include <QStandardPaths>
#include <QDebug>
#include <QGraphicsSceneMouseEvent>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();


protected:
    void contextMenuEvent(QGraphicsSceneContextMenuEvent *contextMenuEvent);

private slots:
    void on_openButton_clicked();
    void showImage(QString imagePath);

private:
    Ui::MainWindow *ui;
    QPixmap image;
    QImage  *imageObject;        
    QGraphicsScene *scene;
    QGraphicsPixmapItem *pixmap;    
};
#endif // MAINWINDOW_H

ademmler

TEMPLATE = app
TARGET = QtMinimalScene

QT  += core gui widgets
CONFIG 	+= c++11

# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

INCLUDEPATH += .

SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h

FORMS += \
    mainwindow.ui

JonB

@ademmler said in QGraphicsScene + Mousevents general question:

void MainWindow::contextMenuEvent(QGraphicsSceneContextMenuEvent *contextMenuEvent)
{
    qDebug() << "QGS Event: " << contextMenuEvent << Qt::endl;
}

What is your question? This is the context menu event for your MainWindow. Not for your QGraphicsScene *scene. If that is what you wanted.

If you don't want to sub-class (is that the issue?), you may get the right click/context menu via an eventFilter(), I don't know.

ademmler

@JonB said in QGraphicsScene + Mousevents general question:

If you don't want to sub-class (is that the issue?), you may get the right click/context menu via an eventFilter(), I don't know.

I asked in the beginning if "subclassing" is mandatory to access QGraphicsScene events ...
It seems like that this is the only way.

JonB

@ademmler
In Qt I think you will find the convention that methods with event in the name tend to be protected members which you have to override (and therefore subclass) if you need to modify/be notified of them. That differs from the many signal cases in classes where you can just add your own slot(s) without subclassing.

As I said earlier, it's usually also possible to go via an eventFilter to avoid sub-classing. Did you look into that as an alternative?

ademmler

@JonB said in QGraphicsScene + Mousevents general question:

eventFilter

I will soon and let you know - thank you.