After call QGraphicsScene::advance() my item not redrawn - c++

Question

I was trying to do a simple animation on QGrapichScene. I implemented void QGraphicsItem::advance(int) in class, that inherites QGraphicsItem, but after calling advance() my item not redrawn. In colliding mice example it works.
What have I done wrong?
Here is my code:
widget.h:
class Widget : public QWidget
{
Q_OBJECT
private:
QGraphicsScene *scene;
QGraphicsView *view;
QHBoxLayout *layout;
QTimer t;
public:
Widget(QWidget *parent = 0);
~Widget();
};
widget.cpp:
Widget::Widget(QWidget *parent) : QWidget(parent)
{
layout = new QHBoxLayout(this);
view = new QGraphicsView(this);
scene = new QGraphicsScene(0, 0, 400, 400, view);
scene->addItem(new MyItem());
view->setScene(scene);
layout->addWidget(view);
setLayout(layout);
connect(&t, SIGNAL(timeout()), scene, SLOT(advance()));
t.start(100);
}
Widget::~Widget()
{
}
my_item.h:
class MyItem : public QGraphicsItem
{
private:
QRect bRect;
enum directon { left, right };
directon currentDir;
protected:
virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
public:
MyItem(int w = 20);
virtual void advance(int phase);
virtual QRectF boundingRect() const
{ return QRectF(bRect); }
};
my_item.cpp:
MyItem::MyItem(int w)
{
currentDir = right;
bRect = QRect(0, 0, w, w);
}
void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
qDebug() << "In void MyItem::paint(QPainter*, "
"const QStyleOptionGraphicsItem*, "
"QWidget*)";
painter->fillRect(bRect, Qt::red);
}
void MyItem::advance(int phase)
{
qDebug() << "In void MyItem::advance(int);"
<< "Phase =" << phase;
if(!phase)
return;
// Than move item to new positon...
}

Answer 1

It's on you to inform the graphics scene that your item's contents have changed. You have to call update() at the end of advance(). If you're simply moving the item, without changing its contents, then you don't need to call update() of course - the scene will detect such changes automatically.

Answer 2

I found something strange:
connect(&timer, SIGNAL(timeout()), scene, SLOT(advance()));
The slot need to combined after the Widget is shown, or the slot will never been called!
As the Qt example shown, you can combine it in the main function.