Hello,

I'd like to do a program, which allows user to "arrange" nodes (QGraphicsObjects) on screen (QGraphicsScene / QGraphicsView). Of course this is very simplified description.

Important part of "arranging" is selecting existing nodes by clicking on it. I decided to use QGraphicsItem::setSelected() method. But selected nodes are somehow automatically deselected (and redrawed) after clicking somewhere on screen.

I thought all logic of seleting/deselecting must be added by programmer, because I read documentation for these functions and can't see anythink about it. But maybe I overlooked something?

Thanks

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Here is (again simplified) code I'm using, just with one added node by default. Probably most interesting line is 53, where I select the clicked node:

Qt Code: 
  1. #include <QtGui>
  2. #include <QtGui/QGraphicsView>
  3. #include <QMouseEvent>
  4. #include <QRectF>
  5. #include <QPainterPath>
  6. #include <QPainter>
  7. #include <QStyleOptionGraphicsItem>
  8. #include <QWidget>
  9. #include <QColor>
  10. #include <QGraphicsScene>
  11. #include <QGraphicsObject>
  12. #include <QGraphicsSceneMouseEvent>
  13.  
  14. class Node : public QGraphicsObject
  15. {
  16. public:
  17. 	Node() { setFlag(ItemIsSelectable); }
  18.  
  19. 	QRectF boundingRect() const
  20. 	{
  21. 		qreal adjust = 2;
  22. 		return QRectF(-10 - adjust, -10 - adjust, 23 + adjust, 23 + adjust);
  23. 	}
  24.  
  25.     QPainterPath shape() const
  26. 	{
  28. 		path.addEllipse(-10, -10, 20, 20);
  29. 		return path;
  30. 	}
  31.  
  32. 	void paint( QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget )
  33. 	{
  34. 		QColor fill, stroke;
  35.  
  36. 		if( this->isSelected() ) {
  37. 			fill = Qt::yellow;
  38. 			stroke = Qt::gray;
  39. 		}
  40. 		else {
  41. 			fill = Qt::green;
  42. 			stroke = Qt::black;
  43. 		}
  44.  
  45. 		painter->setBrush(fill);
  46. 		painter->setPen(QPen( stroke, 0));
  47. 		painter->drawEllipse(-10, -10, 20, 20);
  48. 	}
  49.  
  50. protected:
  51. 	void mouseReleaseEvent( QGraphicsSceneMouseEvent *event )
  52. 	{
  53. 		this->setSelected( !this->isSelected() );
  54. 		this->update( this->boundingRect() );
  55. 		event->accept();
  56. 	}
  57.  
  58. 	void mousePressEvent( QGraphicsSceneMouseEvent *event )
  59. 	{
  60. 	}
  61. };
  62.  
  63. class Playground : public QGraphicsView
  64. {
  65. public:
  66. 	Playground()
  67. 	{
  68. 		QGraphicsScene * scene = new QGraphicsScene( this );
  69. 		scene->setItemIndexMethod(QGraphicsScene::NoIndex);
  70. 		scene->setSceneRect(0, 0, 200, 200);
  71. 		this->setScene(scene);
  72.  
  73. 		Node *newNode = new Node();
  74. 		scene->addItem( newNode );
  75. 		newNode->setPos( 100, 100 );
  76. 	}
  77.  
  78. protected:
  79.  
  80. 	void drawBackground( QPainter *painter, const QRectF &rect )
  81. 	{
  82. 		setInteractive ( true );
  83. 		QRectF sceneRect = this->sceneRect();
  84. 		painter->fillRect(rect.intersect(sceneRect), Qt::gray);
  85. 		painter->setBrush(Qt::NoBrush);
  86. 		painter->drawRect(sceneRect);
  87. 	}
  88. };
  89.  
  90.  
  91. int main(int argc, char **argv)
  92. {
  93.     QApplication app(argc, argv);
  94.  
  95. 	Playground playground;
  96. 	playground.show();
  97.  
  98. 	return app.exec();
  99. }
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