is event always accepted in QGraphicsView::wheelEvent()?

odelaune

Hello, I have a very similar situation to the one described in this post., i.e. I have QGraphicsWidgets in a QGraphicsScene rendered through a QGraphicsView and I would like to zoom in/out using the mouse wheel, except when I scroll on a QGraphicsWidget.

But, the solution proposed by kshegunov does not work because the QWheelEvent status is always true.

So I have written a snippet to try to understand what happen. Here is the code
CMakeLists.txt

cmake_minimum_required(VERSION 3.5)

project(test LANGUAGES CXX)

set(CMAKE_AUTOMOC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 COMPONENTS REQUIRED Core Widgets)

set(SOURCE_FILES
  main.cpp
  view.cpp
  )

add_executable(test ${SOURCE_FILES})

target_link_libraries(test PRIVATE
  Qt6::Core
  Qt6::Widgets)

main.cpp

// Qt headers
#include <QApplication>
#include <QGraphicsRectItem>

#include "view.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QGraphicsScene scene;
    View v;
    v.setScene(&scene);

    QGraphicsRectItem *bkg_item = new QGraphicsRectItem();
    bkg_item->setBrush(QBrush(QColorConstants::White, Qt::SolidPattern));
    bkg_item->setRect(QRectF(0, 0, 1000, 1000));
    scene.addItem(bkg_item);
    
    v.show();
    return app.exec();
}

view.cpp

#include "view.h"

#include <QWheelEvent>

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


void View::wheelEvent(QWheelEvent* event)
{
  qDebug() << Q_FUNC_INFO << "accepted?" << event->isAccepted();
  QGraphicsView::wheelEvent(event);
}

view.h

#ifndef VIEW_H
#define VIEW_H

#include <QGraphicsView>

class View : public QGraphicsView
{
  Q_OBJECT
  
public:
  explicit View(QWidget* widget = nullptr);
  
protected:
  void wheelEvent(QWheelEvent* event) override;
};
  
#endif // VIEW_H

When I run this code and when I scroll, I always get:
virtual void View::wheelEvent(QWheelEvent) accepted? true

So, if the QWheelEvent is already true when I entered in wheelEvent(), how could it be false later, for example in the wheelEvent() of my QGraphicsWidget?

Am I missing something?

jsulm

@odelaune said in is event always accepted in QGraphicsView::wheelEvent()?:

status is always true

That's because @kshegunov calls event->isAccepted() AFTER calling QGraphicsView::wheelEvent(event);

odelaune

@jsulm
Indeed! Thank you for your reply.