mouse tracking in QGraphicsItem

[christina123y]

First ,let me explain what problem I have countered.
I use QGraphicsView Frame.I create a class Cordinate which inherits from QGraphicsItem.This class's main work is to draw a Cordinate System.
Now I want to track mouse postion in this cordinate system. While I implement mouseMoveEvent(QGraphicsSceneMouseEvent * event), and
mousePressEvent(QGraphicsSceneMouseEvent * event) in this Cordinate class. And here is my code :

void Cordinate::mouseMoveEvent(QGraphicsSceneMouseEvent * event)
{
	QGraphicsItem::mouseMoveEvent(event);
        float x = event->pos().x;
 	qDebug() << "mouse move " << endl;
}
void Cordinate::mousePressEvent(QGraphicsSceneMouseEvent * event)
{
	QGraphicsItem::mousePressEvent(event);
	QPointF point = event->pos();
        qDebug()<<"mouse press point is ("<< point.x() <<", "<<point.y()<<")"<<endl;
}

void Cordinate::mouseMoveEvent(QGraphicsSceneMouseEvent * event)
{
	QGraphicsItem::mouseMoveEvent(event);
        float x = event->pos().x;
 	qDebug() << "mouse move " << endl;
}
void Cordinate::mousePressEvent(QGraphicsSceneMouseEvent * event)
{
	QGraphicsItem::mousePressEvent(event);
	QPointF point = event->pos();
        qDebug()<<"mouse press point is ("<< point.x() <<", "<<point.y()<<")"<<endl;
}

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And when run, the console print out the mouse press point ,but doesn't print out the mouse move?
Why?Doesn's the item grab the mouse move event? And how I can work out this problem?
Wish your help, please! Thank you very much!

Oh, last and the most ,I have another class which is Cordinate class's child item!