QWidget keyPressEvent override - c++

Question

I'm trying for half an eternity now overriding QWidgets keyPressEvent function in QT but it just won't work. I've to say i am new to CPP, but I know ObjC and standard C.
My problem looks like this:
class QSGameBoard : public QWidget {
Q_OBJECT
public:
QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s);
signals:
void keyCaught(QKeyEvent *e);
protected:
virtual void keyPressEvent(QKeyEvent *event);
};
QSGameBoard is my QWidget subclass and i need to override the keyPressEvent and fire a SIGNAL on each event to notify some registered objects.
My overridden keyPressEvent in QSGameBoard.cpp looks like this:
void QSGameBoard::keyPressEvent(QKeyEvent *event) {
printf("\nkey event in board: %i", event->key());
//emit keyCaught(event);
}
When i change QSGameBoard:: to QWidget:: it receives the events, but i cant emit the signal because the compiler complains about the scope. And if i write it like this the function doesn't get called at all.
What's the problem here?

Answer 1

EDIT:
As pointed out by other users, the method I outlined originally is not the proper way to resolve this.
Answer by Vasco Rinaldo
Use Set the FocusPolicy to Qt::ClickFocus to get the keybordfocus by
mouse klick. setFocusPolicy(Qt::ClickFocus);
The previous (albeit imperfect) solution I gave is given below:
Looks like your widget is not getting "focus". Override your mouse press event:
void QSGameBoard::mousePressEvent ( QMouseEvent * event ){
printf("\nMouse in board");
setFocus();
}
Here's the source code for a working example:
QSGameBoard.h
#ifndef _QSGAMEBOARD_H
#define _QSGAMEBOARD_H
#include <QWidget>
#include <QGraphicsScene>
class QSGameBoard : public QWidget {
Q_OBJECT
public:
QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s);
signals:
void keyCaught(QKeyEvent *e);
protected:
virtual void keyPressEvent(QKeyEvent *event);
void mousePressEvent ( QMouseEvent * event );
};
#endif /* _QSGAMEBOARD_H */
QSGameBoard.cpp
#include <QKeyEvent>
#include <QLabel>
#include <QtGui/qgridlayout.h>
#include <QGridLayout>
#include "QSGameBoard.h"
QSGameBoard::QSGameBoard(QWidget* p, int w, int h, QGraphicsScene* s) :
QWidget(p){
QLabel* o = new QLabel(tr("Test Test Test"));
QGridLayout* g = new QGridLayout(this);
g->addWidget(o);
}
void QSGameBoard::keyPressEvent(QKeyEvent* event){
printf("\nkey event in board: %i", event->key());
}
void QSGameBoard::mousePressEvent ( QMouseEvent * event ){
printf("\nMouse in board");
setFocus();
}
main.cpp
#include <QtGui/QApplication>
#include <QtGui/qmainwindow.h>
#include "QSGameBoard.h"
int main(int argc, char *argv[]) {
// initialize resources, if needed
// Q_INIT_RESOURCE(resfile);
QApplication app(argc, argv);
QMainWindow oM;
QGraphicsScene o;
QSGameBoard a(&oM, 1, 2, &o);
oM.setCentralWidget(&a);
a.show();
oM.show();
// create and show your widgets here
return app.exec();
}

Answer 2

You don't have to reimplement mousePressEvent yourself just to call setFocus. Qt planed it already.
Set the FocusPolicy to Qt::ClickFocus to get the keybordfocus by mouse klick.
setFocusPolicy(Qt::ClickFocus);
As said in the manual:
This property holds the way the widget accepts keyboard focus.
The policy is Qt::TabFocus if the widget accepts keyboard focus by tabbing, Qt::ClickFocus if the widget accepts focus by clicking, Qt::StrongFocus if it accepts both, and Qt::NoFocus (the default) if it does not accept focus at all.
You must enable keyboard focus for a widget if it processes keyboard events. This is normally done from the widget's constructor. For instance, the QLineEdit constructor calls setFocusPolicy(Qt::StrongFocus).
If the widget has a focus proxy, then the focus policy will be propagated to it.

Answer 3

Set the FocusPolicy to Qt::ClickFocus to get the keybordfocus by mouse klick.
setFocusPolicy(Qt::ClickFocus);