QGraphicsItem repaint

Question

I want to change text color inside a rectangle periodically. Here is my trial:

 TrainIdBox::TrainIdBox()
 {
   boxRect = QRectF(0,0,40,15);
   testPen = QPen(Qt:red);
   i=0;
   startTimer(500);
 }

QRectF TrainIdBox::boundingRect() const
{
 return boxRect;
}

void TrainIdBox::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,   QWidget *widget)
{
  Q_UNUSED(widget);
  Q_UNUSED(option);

  painter->setPen(QPen(drawingColor,2));
  painter->drawRect(boxRect);
  painter->setPen(testPen);
  painter->drawText(boxRect,Qt::AlignCenter,"TEST");

 }
 void TrainIdBox::timerEvent(QTimerEvent *te)
 {
  testPen = i % 2 == 0 ? QPen(Qt::green) : QPen(Qt::yellow);
  i++;
  update(boxRect);
 }

This code does not working properly. What is wrong?

Answer 1

QGraphicsItem is not derived from QObject and hence does not have an event queue, which is needed to handle timer events. Try using QGraphicsObject or multiple inheritance of QGraphicsItem and QObject (which is exactly what QGraphicsObject does).

Answer 2

If you inherit from QGraphicsObject ... I give here an example:

Declare:

 class Text : public QGraphicsObject
    {
        Q_OBJECT

    public:
        Text(QGraphicsItem * parent = 0);
        void paint ( QPainter * painter,
                     const QStyleOptionGraphicsItem * option, QWidget * widget  );
        QRectF boundingRect() const ;
        void timerEvent ( QTimerEvent * event );

    protected:
        QGraphicsTextItem * item;
        int time;
    };

implementation:

Text::Text(QGraphicsItem * parent)
    :QGraphicsObject(parent)
{
    item = new QGraphicsTextItem(this);
    item->setPlainText("hello world");

    setFlag(QGraphicsItem::ItemIsFocusable);    
    time  = 1000;
    startTimer(time);
}

void Text::paint ( QPainter * painter,
                   const QStyleOptionGraphicsItem * option, QWidget * widget  )
{
    item->paint(painter,option,widget);    
}

QRectF Text::boundingRect() const
{
    return item->boundingRect();
}

void Text::timerEvent ( QTimerEvent * event )
{
    QString timepass = "Time :" + QString::number(time / 1000) + " seconds";
    time = time + 1000;
    qDebug() <<  timepass;
}

good luck

Answer 3

Check if Timer was properly initialized, it shouldn't return 0.

Try also changing color of brush used to paint.

I check your code when I get some free time in home, but that won't be before Sunday.

Answer 4

As the base point, you could watch Wiggly Example and find some errors in you code yourself, what is much better. For Qt, in my opinion, it's a good practice to look sometimes in Examples and Demos application.

Good luck!