I understood why the image wasn't displayed. I should wrote QFrame instead of QGraphicsView.

Qt Code: 
  1. view->setStyleSheet("QFrame { background-image: url(grid.png) ;"
  2. 				"background-repeat: repeat }");
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But I don't understand what is doing background-repeat option.
Is it repeat background image without scaling??? (I don't think so)

Here I want to show how I do zoom operation.

Qt Code: 
  1. void LayoutEditor::zoomIn()
  2. {
  3. 	scaleFactor *= 1.25;
  4. 	view->scale(1.25, 1.25);
  5. 	if(scaleFactor >= 1.0) {
  6. 		// which function to use??????
  7. 		//view->setBackgroundBrush(QBrush(QPixmap("Resources\\grid.png")));
  8. 		//view->setStyleSheet("QFrame { background-image: url(grid.png) ;"
  9. 						"background-repeat: repeat }");
  10. 	}
  11. 	...
  12.  
  13. }
  14.  
  15. void LayoutEditor::zoomOut()
  16. {
  17. 	scaleFactor *= 0.8;
  18. 	view->scale(0.8, 0.8);
  19. 	if(scaleFactor < 1.0) {
  20. 		view->setBackgroundBrush(QBrush(Qt::black));
  21. 	}	
  22. 	...
  23.  
  24. }
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