Signal / Slot from QGraphicsItem

Hi,

I have the following code declared in my QGraphicsScene derived class:

Code:

---

connect( pItem, SIGNAL(ShowOptions()),this,SLOT(ShowCanOptions()) );

---

Where pItem is an object derived from QGraphicsItem.

I get a conversion error on pItem - does this have to be derived from QObject?

Regards,
Steve

Yes, your item class have to be derived from QObject too. Note that you have to inherit from QObject first and then from QGraphicsIiem:

class MyGraphicsItem : public QObject, public QGraphicsItem {
Q_OBJECT
...
};

Yes, and make sure QObject is first in the base class list.
Also don't forget to add the Q_OBJECT macro.

Thanks Marcel, I did try that but still get the type conversion error.

This is my derived graphics item class :

Code:

---

class CCanGraphicsItem : public QObject, public QGraphicsItem
{
	Q_OBJECT
 
public:
	CCanGraphicsItem( int x, int y, QString strText ) : m_rect( 10, 10, 200, 100 ), m_color( QColor(255,255,255,255) )
	{
		m_strText = strText;
		setPos( x, y );
		m_pFont = new QFont("Times", 20, QFont::Bold );
		setFlag(QGraphicsItem::ItemIsMovable, true);
		setFlag(QGraphicsItem::ItemIsSelectable, true);
	}
	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) 
	{
		//  painter->setRenderHint(QPainter::Antialiasing, true);
		setFlag(QGraphicsItem::ItemIsMovable, true);
		painter->setFont( *m_pFont );
		painter->setPen(Qt::SolidLine);
		painter->setBrush(m_color);
		painter->drawRoundRect( m_rect );//10, 10, 100, 100);
		painter->drawText( 20, 20, 190, 90, Qt::AlignCenter, m_strText );//, m_rect );
	}
 
	QRectF boundingRect() const { return m_rect; }
 
signals:
	void ShowOptions();
 
protected:
	void mouseDoubleClickEvent ( QGraphicsSceneMouseEvent * event ) 
	{
		QMessageBox::information(0, "This", m_strText );
		emit ShowOptions();
	}
 
    void contextMenuEvent(QContextMenuEvent *event)
	{
	}
 
	QRectF m_rect;
	QColor m_color;
	QString m_strText;
	QFont* m_pFont;
};

---

and the full code that tries to do the signal/slot connection :

Code:

---

void CanScene::AddBoxItem( int x, int y, QString strText, ITEMS item )
{
	QGraphicsItem* pItem = NULL;
 
	switch( item )
	{
	case CAN :
		addItem( pItem = new CCanGraphicsItem( x, y, strText ) );
		QObject::connect( pItem, SIGNAL(ShowOptions()),this,SLOT(ShowCanOptions()) );
		break;
// etc...
	}
}

---

Something I'm obviously doing wrong?!

Regards,
Steve

Because the pItem is actually only a QGraphicsItem. It does not now about your signal.
Change the type of pItem to CCanGraphicsItem.

Ooops :p

How I didn't notice that?!

Regards,
Steve

I don't think this is a problem, at least not during compile time.

steg90: What exactly is the error?

The error was most likely QObject::connect no such signal...etc

I wouldn't call that a conversion error :) I expected a "Cannot convert ..." message.

Hi guys,

Exact error was :

\CanScene.cpp(17) : error C2664: 'bool QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)' : cannot convert parameter 1 from 'QGraphicsItem *' to 'const QObject *'
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

Regards,
Steve

Oh, yes in that case changing the type will help, because QGraphicsItem is not a QObject thus it can't be used with connect().