i inherit form QGraphicsitem.but it dosen't show on my QGraphicsView,
Qt Code: 
  1. #ifndef LINEITEM_H
  2. #define LINEITEM_H
  3.  
  4. #include <QGraphicsItem.>
  5. #include <QPen>
  6. #include <QPainter>
  7.  
  8. class LineItem :public QGraphicsItem
  9. {
  10.  
  11.  
  12. public:
  13. 	LineItem( QGraphicsItem * parent = 0);
  14. 	LineItem( const QLineF & line, QGraphicsItem * parent = 0 );
  15. 	LineItem( qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem * parent = 0 );
  16. 	~LineItem();
  17. 	//
  18. 	QLineF	line ( ) const;
  19. 	QPen getPen()const;
  20. 	void setLine( const QLineF & line );
  21. 	void setLine( qreal x1, qreal y1, qreal x2, qreal y2 );
  22. 	void setPen( const QPen & pen );
  23.  
  24. 	QRectF boundingRect() const;
  25. 	void QGraphicsItem::paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );
  26. 	QPainterPath shape () const ;
  27.  
  28.  
  29. private:
  30. 	QPointF startPoint;
  31. 	QPointF centerPoint;
  32. 	QPointF endPoint;
  33.  
  34. 	QPen pen;
  35.  
  36. };
  37.  
  38. #endif // LINEITEM_H
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Qt Code: 
  1. #include "LineItem.h"
  2.  
  3. LineItem::LineItem( QGraphicsItem * parent)
  4. 	: QGraphicsItem( parent)
  5. {
  6.  
  7. }
  8.  
  9. LineItem::LineItem( const QLineF & line, QGraphicsItem * parent  ):QGraphicsItem(parent)
  10. {
  11. 	startPoint=line.p1();
  12. 	endPoint=line.p2();
  13. 	centerPoint=QPointF((startPoint.x()+endPoint.y())/2,(startPoint.y()+endPoint.y())/2);
  14. 	pen=QPen(Qt::black);
  15. }
  16.  
  17. LineItem::LineItem( qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem * parent /* = 0 */ ):QGraphicsItem(parent)
  18. {
  19. 	startPoint=QPointF(x1,y1);
  20. 	endPoint=QPointF(x2,y2);
  21. 	centerPoint=QPointF((x1+x2)/2,(y1+y2)/2);
  22. }
  23.  
  24.  
  25. LineItem::~LineItem()
  26. {
  27.  
  28. }
  29.  
  30. QRectF LineItem::boundingRect() const
  31. {
  32. 	return QRectF(startPoint,endPoint);
  33.  
  34. }
  35.  
  36. QPainterPath LineItem::shape() const
  37. {
  39. 	path.addRect(QRectF(startPoint,endPoint));
  40. 	return path;
  41. }
  42.  
  43. QPen LineItem::getPen() const
  44. {
  45. 	return pen;
  46. }
  47.  
  48. void LineItem::setPen( const QPen & pen )
  49. {
  50. 	this->pen=pen;
  51. }
  52.  
  53. void LineItem::setLine( const QLineF & line )
  54. {
  55. 	startPoint=line.p1();
  56. 	endPoint=line.p2();
  57. 	centerPoint=QPointF((startPoint.x()+endPoint.y())/2,(startPoint.y()+endPoint.y())/2);
  58. }
  59.  
  60. void LineItem::setLine( qreal x1, qreal y1, qreal x2, qreal y2 )
  61. {
  62. 	startPoint=QPointF(x1,y1);
  63. 	endPoint=QPointF(x2,y2);
  64. }
  65.  
  66. void LineItem::paint( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget /* = 0 */ )
  67. {
  68. 	/*painter->setPen(QPen(Qt::green, 3, Qt::DashDotLine, Qt::RoundCap, Qt::RoundJoin));
  69. 	painter->drawRect(startPoint.x()-2,startPoint.y(),4,4);*/
  70. 	//painter->drawPoint(startPoint);
  71. 	//painter->drawPoint(endPoint);
  72. 	//painter->drawPoint(centerPoint);
  73.  
  74. 	painter->setPen(Qt::blue);
  75. 	painter->setFont(QFont("Arial", 30));
  76. 	painter->drawText(QRectF(startPoint,endPoint), Qt::AlignCenter, "Qt");
  77.  
  78. }
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