Keyboard input in custom QQuickPaintedItem - c++

Question

I defined my custom QQuickPaintedItem in such a way:
class NiceItem : public QQuickPaintedItem
{
...
public:
...
void keyPressEvent(QKeyEvent * event);
void paint(QPainter *painter);
...
};
Here you have keyPressEventcode:
void NiceItem::keyPressEvent(QKeyEvent * event)
{
if(event->key() == Qt::Key_Left)
playerX--;
else if(event->key() == Qt::Key_Right)
playerX++;
else if(event->key() == Qt::Key_Up)
playerY--;
else if(event->key() == Qt::Key_Down)
playerY++;
}
Here's paint code:
void NiceItem::paint(QPainter *painter)
{
QPen pen(m_color, 2);
painter->setPen(pen);
QRectF rectangle(playerX, playerY, 80.0, 60.0);
painter->drawRect(rectangle);
update();
}
As you can see code is really simple. Rectangle is successfully drawn on the screen, but pressing arrows does nothing. Is this a wrong method? If so, how can I process the keyboard input?

Answer 1

For an Item to receive the mouse event, it must meet the following:
Have the flag QQuickItem::ItemIsFocusScope enabled.
Having focus, this can be done in C++ with setFocus(true) or in QML: focus: true.
On the other hand, if your objective is to draw a rectangle on the window, then you have an error in the concept of what coordinates are used for the painting, the painting uses the local coordinates and not the window or screen. So instead of creating new attributes you should only use position(), x(), y() (and their setters) to modify the geometry since these elements are with respect to the parent's coordinates.
#ifndef NICEITEM_H
#define NICEITEM_H
#include <QQuickPaintedItem>
class NiceItem : public QQuickPaintedItem
{
Q_OBJECT
public:
NiceItem(QQuickItem *parent=nullptr);
void paint(QPainter *painter);
protected:
void keyPressEvent(QKeyEvent *event);
private:
QColor m_color;
};
#endif // NICEITEM_H
#include "niceitem.h"
#include <QPainter>
#include <QPen>
NiceItem::NiceItem(QQuickItem *parent):
QQuickPaintedItem(parent), m_color(QColor("red"))
{
setFlag(QQuickItem::ItemIsFocusScope, true);
setFocus(true);
setSize(QSizeF(80.0, 60.0));
}
void NiceItem::paint(QPainter *painter)
{
QPen pen(m_color, 2);
painter->setPen(pen);
painter->drawRect(boundingRect());
}
void NiceItem::keyPressEvent(QKeyEvent *event)
{
QPointF delta;
if(event->key() == Qt::Key_Left)
delta = QPointF(-1, 0);
else if(event->key() == Qt::Key_Right)
delta = QPointF(+1, 0);
else if(event->key() == Qt::Key_Up)
delta = QPointF(0, -1);
else if(event->key() == Qt::Key_Down)
delta = QPointF(0, +1);
setPosition(position() + delta);
}