Qt: Have parent decide whether or not a child accepts event - c++

Question

I am having an issue trying to get a parent object to filter child events.
In the following example, I set up an event filter on a spin box. The event filter detects mouse press events on the spin box. I would then like the parent object to accept or ignore that event, based on some criteria.
The problem is that it seems to accept the mouse press event and then ignore the mouse release event. This is an issue with mouse wheel events.
How can I have my parent accept/ignore the event?
In the real case, the message has to be passed through more layers, but the behavior is the same. If you click the up arrow on the spin box, the message will popup and then the numbers will start spinning.
Qt version: 5.6.1
#include "mainwindow.h"
#include <QEvent>
#include <QSpinBox>
#include <QHBoxLayout>
#include <QMessageBox>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QSpinBox* spinner = new QSpinBox;
QHBoxLayout* layout = new QHBoxLayout;
QWidget* widget = new QWidget;
layout->addWidget(spinner);
spinner->installEventFilter(this);
connect(this, SIGNAL(mouse_pressed(QEvent*)),
this, SLOT(handle_event(QEvent*)));
widget->setLayout(layout);
setCentralWidget(widget);
}
MainWindow::~MainWindow()
{
}
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
if (event->type() == QEvent::MouseButtonPress
event->type() == QEvent::Wheel)
{
emit mouse_pressed(event);
}
return QMainWindow::eventFilter(watched, event);
}
void MainWindow::handle_event(QEvent* event)
{
event->ignore();
QMessageBox(QMessageBox::Warning, "warning", "ignoring event").exec();
}
Edit 1: I have found a way to partially stop the event cascade. In MainWindow::handle_event(...), rather than calling 'event->ignore()', I call 'event->setAccepted(false)', then check for for 'event->isAccepted()' in the eventFilter. If it is not accepted, I ignore the event.
This solution has worked well for QLineEdit, but it is still not working as expected with QSpinBox and QPushbutton. For QSpinBox, a wheel event still changes the value and clicking the spin buttons result in sustained spinning (no mouse release being detected). For QPushButton, the event is ignored but the button stays depressed.
Edit 2: Returning false after ignoring the event blocks the cascade. Thanks #G.M. for the hint! I will post an answer.

Answer 1

The way to get the parent to decide whether or not a child should handle an event was to call 'event->setAccepted(false)', the check for the in the eventFilter function. If it is false, ignore the event and return true from the function.
Return true from the eventFilter function was counterintuitive to me, but its right there in the documentation. Event filters are much less invasive than subclassing, so I was glad to come to a solution.
#include "mainwindow.h"
#include <QEvent>
#include <QSpinBox>
#include <QHBoxLayout>
#include <QMessageBox>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QSpinBox* spinner = new QSpinBox;
QHBoxLayout* layout = new QHBoxLayout;
QWidget* widget = new QWidget;
layout->addWidget(spinner);
spinner->installEventFilter(this);
connect(this, SIGNAL(mouse_pressed(QEvent*)),
this, SLOT(handle_event(QEvent*)));
widget->setLayout(layout);
setCentralWidget(widget);
}
MainWindow::~MainWindow()
{
}
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
if (event->type() == QEvent::MouseButtonPress
event->type() == QEvent::Wheel)
{
emit mouse_pressed(event);
if (!event->isAccepted())
{
event->ignore();
return true;
}
}
return QMainWindow::eventFilter(watched, event);
}
void MainWindow::handle_event(QEvent* event)
{
event->setAccepted(false);
QMessageBox(QMessageBox::Warning, "warning", "ignoring event").exec();
}