overriding paint() and mouseEvents() of a QGraphicsItem - c++

Question

In Qt, I'm trying to highlight an item when I'm clicking it and then draw a line from its end to the current cursor position. I can either highlight it or draw the line, but not both. Here are my classes :
// ucPin.h
#pragma once
#include "stdafx.h"
class ucPin : public QGraphicsLineItem{
qreal x1, y1, x2, y2;
bool isClicked;
QGraphicsLineItem * li;
public :
ucPin (qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem *parent = 0);
void paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget );
void mousePressEvent (QGraphicsSceneMouseEvent * event);
void mouseReleaseEvent (QGraphicsSceneMouseEvent *event);
void mouseMoveEvent (QGraphicsSceneMouseEvent *event);
};
// ucPin.cpp
#include "ucPin.h"
ucPin::ucPin (qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem *parent) :
QGraphicsLineItem(x1, y1, x2, y2, parent){
this->x1 = x1; this->y1 = y1; this->x2 = x2; this->y2 = y2;
this->setFlags(QGraphicsItem::ItemIsFocusable
| QGraphicsItem::ItemIsSelectable);
isClicked = false;
li = NULL;
}
void ucPin::paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget )
{
QStyleOptionGraphicsItem newOption (*option);
newOption.state =QStyle::State_None;
QGraphicsLineItem::paint(painter, &newOption, widget);
//painter-> setRenderHint(QPainter::Antialiasing);
if (option->state & QStyle::State_Selected) {
QPen outline;
outline.setColor(Qt::green);
outline.setWidth(6);
setPen(outline);
}
else{
QPen outline; outline.setWidth(3);
setPen(outline);
}
}
void ucPin::mousePressEvent(QGraphicsSceneMouseEvent* event) {
/*QPointF pos = event->pos();
QGraphicsLineItem * li = new QGraphicsLineItem(0,0, pos.x(), pos.y(), this);*/
isClicked = true;
}
void ucPin::mouseReleaseEvent(QGraphicsSceneMouseEvent* event) {
isClicked = false;
}
void ucPin::mouseMoveEvent(QGraphicsSceneMouseEvent* event) {
if(NULL != li) { delete li; li = NULL;}
li = new QGraphicsLineItem(0,0, event->pos().x(), event->pos().y(), this);
}
I guess when implementing the mouseEvent overrides, the paint event for the selected state doesn't get called? How can one work around this?

Answer 1

In order to request the repainting of your QGraphicsItem, you need to call update() whenever the appearance changes. The setSelected is called in QGraphicsItem::mousePressEvent, so you need to propagate it to the base class calling QGraphicsLineItem::mousePressEvent(event) in your overriden mousePressEvent. Same goes for mouseReleaseEvent. Or you could handle the selection state yourself, but you shouldn't unless there's a really good reason for that. Also, I think it might make sense to set your pens before calling QGraphicsLineItem::paint(...).
Also, it is inefficient to allocate a new li every time the mouse moves - just allocate it once and use setLine to set the new coordinates.