Hi!

Thanks for your replies.

But my Problem is still not solved.

I have changed my strategy a bit:
I am extensively working on a QGraphicsView and Scene, so the idea is to hide all QGraphicsItems in my scene once the computation starts, and to show a Progressbar which is a subclass of QGraphicsItem.

the code looks like that:
Qt Code: 
  1. //MainView is derived from QGraphicsView
  2. void MainView::loadBackgroundImage(const QString& filename)
  3. {
  4. 	// the background item shall always be newly created.
  5. 	if(this->scene()->items().contains(this->m_background))
  6. 		this->scene()->removeItem(this->m_background);
  7. 	delete m_background;
  8.  
  9. 	//hide all scene items
  10. 	this->m_scalable_item->setVisible(false);
  11.  
  12. 	//get the progressbar (derived from QGraphicsItem)
  13. 	GraphicsProgressBar * g = new GraphicsProgressBar;
  14. 	this->scene()->addItem(g);
  15. 	g->setPos(this->sceneRect().center());
  16.  
  17. 	this->scene()->update();
  18.  
  19. 	QTimer * timer = new QTimer(this);
  20. 	connect(timer, SIGNAL(timeout()), g, SLOT(updateProgress()));
  21. 	timer->start(100);
  22.  
  23. 	//BackgroundImageItem is derived from QObject, QThread and QGraphicsItem
  24. 	// start() starts the computation is background-thread
  25. 	m_background = new BackgroundImageItem(filename);
  26. 	m_background->start();
  27. 	qDebug() << "work started";
  28. 	//the gui thread should wait here until the worker has finished
  29. 	m_background->wait();
  30. 	qDebug() << QThread::currentThreadId() << "Waiting done.";
  31.  
  32. 	// I just add the background item here
  33. 	this->scene()->addItem(this->m_background);
  34. 	if(!this->scene()->items().contains(m_scalable_item))
  35. 		this->scene()->addItem(m_scalable_item);
  36. 	this->m_scalable_item->setVisible(true);
  37.  
  38. 	//free all timer resoureces and the progressbar
  39. 	timer->stop();
  40. 	timer->disconnect();
  41. 	g->disconnect();
  42. 	this->scene()->removeItem(g);
  43. 	delete g;
  44. 	delete timer;
  45. }
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The Progressbar code looks like:
Qt Code: 
  1. class GraphicsProgressBar : public QObject,  public QGraphicsItem
  2. {
  3. 	Q_OBJECT
  4.  
  5. public:
  6.  
  7. 	GraphicsProgressBar()
  8. 	{
  9. 		setZValue(5);
  10. 		status = 1;
  11. 	};
  12.  
  13. 	inline QRectF boundingRect() const { return QRectF(-66,-21,132,42); };
  14.  
  15. 	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  16. 	{
  17. 		qDebug() << "paint";
  18. 		painter->drawRect(-66,-21,132,42);
  19. 		if(status >=1)
  20. 			painter->drawRect(-65,-20,40,40);
  21. 		if(status >=2)
  22. 			painter->drawRect(-20,-20,40,40);
  23. 		if(status >=3)
  24. 			painter->drawRect(25,-20,40,40);
  25. 	};
  26.  
  27. public slots:
  28.  
  29. 	void updateProgress()
  30. 	{
  31. 		status = (status+1)%4;
  32. 		qDebug() << QThread::currentThreadId() << status;
  33. 		//this->update();
  34. 	};
  35.  
  36.  
  37. private:
  38. 	int status;
  39. };
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The progressbar does not show up.
Also, the hiding
The paint method gets never called!
Also the debugmsg from updateProgress never appears.
It seems that nothing I try to change at the graphicsScene or view has an effect.
Its not even possible to hide all elements.

HELP appreciated!