Qt5/C++ release mouse during mousePressEvent - c++

Question

I've a QGridLayout where each cell contains my custom widget QFrameExtended defined as follow:
In .h:
#ifndef QFRAMEEXTENDED_H
#define QFRAMEEXTENDED_H
#include <QObject>
#include <QFrame>
class QFrameExtended : public QFrame
{
Q_OBJECT
private:
public:
int id;
explicit QFrameExtended(QWidget *parent = 0);
signals:
void mousePressEvent(QMouseEvent *);
void mouseReleaseEvent(QMouseEvent *);
void pressed(QFrameExtended *);
void released(QFrameExtended *);
public slots:
void on_mouse_press();
void on_mouse_release();
};
#endif // QFRAMEEXTENDED_H
In .cpp:
#include "qframe_extended.h"
QFrameExtended::QFrameExtended(QWidget *parent) : QFrame(parent)
{
this->id = /* Imagine here there is a function to generate an id */ ;
connect( this, SIGNAL( mousePressEvent(QMouseEvent*) ), this, SLOT( on_mouse_press() ) );
connect( this, SIGNAL( mouseReleaseEvent(QMouseEvent*) ), this, SLOT( on_mouse_release() ) );
}
void QFrameExtended::on_mouse_press() {
emit pressed(this);
}
void QFrameExtended::on_mouse_release() {
emit released(this);
}
My form creates the QGridLayout with the QFrameExtended widgets and for each of them defines an event handler:
/* ... */
/* This snippet of code is inside a loop that is creating frame objects */
connect(frame, &QFrameExtended::pressed, this, &MyForm::on_mouse_press);
connect(frame, &QFrameExtended::released, this, &MyForm::on_mouse_release);
/* ... */
and finally these are the event handlers:
void MyForm::on_mouse_press(QFrameExtended *frame) {
qDebug() << "Pressed here: " << frame->id << endl;
}
void MyForm::on_mouse_release(QFrameExtended *frame) {
qDebug() << "Released here: " << frame->id << endl;
}
When I click on a cell (i.e. a QFrameExtended widget) without release the button, I would see printed on the console the id of the cell. After I moved the mouse over another cell, when I release the button I would see printed the second id.
An example is an output like this:
Pressed here: 1
Released here: 3
but the reality is that when I press the mouse button over a QFrameExtended, he starting to grab all mouse events until I release the button. This is the expected behaviour:
Qt automatically grabs the mouse when a mouse button is pressed inside a widget; the widget will continue to receive mouse events until the last mouse button is released.
From: http://doc.qt.io/qt-4.8/qmouseevent.html
How can I change this behaviour? I'll really appreciate if you can give me also an example

Answer 1

Ok, I resolved following the tip of peppe. I tried to extend the QGridLayout but layouts don't support mouse events, because don't inherit from QWidget. So, I extended the QWidget that contains the layout.
In .h:
#ifndef QWIDGETEXTENDED_H
#define QWIDGETEXTENDED_H
#include <QWidget>
#include <QString>
#include <QMouseEvent>
#include "qframe_extended.h"
class QWidgetExtended : public QWidget
{
Q_OBJECT
public:
explicit QWidgetExtended(QWidget *parent = 0);
protected:
virtual void mousePressEvent(QMouseEvent *);
virtual void mouseReleaseEvent(QMouseEvent *);
signals:
void pressed(QFrameExtended *);
void released(QFrameExtended *);
};
#endif
In .cpp:
#include "qwidget_extended.h"
#include "qframe_extended.h"
QWidgetExtended::QWidgetExtended(QWidget *parent) : QWidget(parent)
{
}
void QWidgetExtended::mousePressEvent(QMouseEvent *event) {
QFrameExtended frame;
QWidget *widget = this->childAt(event->pos());
if (widget != NULL) {
QString widgetClassName(widget->metaObject()->className());
//I don't use explicitly the string because if one day someone changes the name of the class, the compiler will output an error
QString className(frame.metaObject()->className());
if (widgetClassName == className) {
emit pressed(dynamic_cast<QFrameExtended*> (widget));
}
}
}
void QWidgetExtended::mouseReleaseEvent(QMouseEvent *event) {
QFrameExtended frame;
QWidget *widget = this->childAt(event->pos());
if (widget != NULL) {
QString widgetClassName(widget->metaObject()->className());
//I don't use explicitly the string because if one day someone changes the name of the class, the compiler will output an error
QString className(frame.metaObject()->className());
if (widgetClassName == className) {
emit released(dynamic_cast<QFrameExtended*> (widget));
}
}
}