Problem inherit from QGraphicItem

i inherit form QGraphicsitem.but it dosen't show on my QGraphicsView,

Code:

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#ifndef LINEITEM_H
#define LINEITEM_H
 
#include <QGraphicsItem.>
#include <QPen>
#include <QPainter>
 
class LineItem :public QGraphicsItem
{
 
 
public:
	LineItem( QGraphicsItem * parent = 0);
	LineItem( const QLineF & line, QGraphicsItem * parent = 0 );
	LineItem( qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem * parent = 0 );
	~LineItem();
	//
	QLineF	line ( ) const;
	QPen getPen()const;
	void setLine( const QLineF & line );
	void setLine( qreal x1, qreal y1, qreal x2, qreal y2 );
	void setPen( const QPen & pen );
 
	QRectF boundingRect() const;
	void QGraphicsItem::paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );
	QPainterPath shape () const ;
 
 
private:
	QPointF startPoint;
	QPointF centerPoint;
	QPointF endPoint;
 
	QPen pen;
 
};
 
#endif // LINEITEM_H

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Code:

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#include "LineItem.h"
 
LineItem::LineItem( QGraphicsItem * parent)
	: QGraphicsItem( parent)
{
 
}
 
LineItem::LineItem( const QLineF & line, QGraphicsItem * parent  ):QGraphicsItem(parent)
{
	startPoint=line.p1();
	endPoint=line.p2();
	centerPoint=QPointF((startPoint.x()+endPoint.y())/2,(startPoint.y()+endPoint.y())/2);
	pen=QPen(Qt::black);
}
 
LineItem::LineItem( qreal x1, qreal y1, qreal x2, qreal y2, QGraphicsItem * parent /* = 0 */ ):QGraphicsItem(parent)
{
	startPoint=QPointF(x1,y1);
	endPoint=QPointF(x2,y2);
	centerPoint=QPointF((x1+x2)/2,(y1+y2)/2);
}
 
 
LineItem::~LineItem()
{
 
}
 
QRectF LineItem::boundingRect() const
{
	return QRectF(startPoint,endPoint);
 
}
 
QPainterPath LineItem::shape() const
{
	QPainterPath path;
	path.addRect(QRectF(startPoint,endPoint));
	return path;
}
 
QPen LineItem::getPen() const
{
	return pen;
}
 
void LineItem::setPen( const QPen & pen )
{
	this->pen=pen;
}
 
void LineItem::setLine( const QLineF & line )
{
	startPoint=line.p1();
	endPoint=line.p2();
	centerPoint=QPointF((startPoint.x()+endPoint.y())/2,(startPoint.y()+endPoint.y())/2);
}
 
void LineItem::setLine( qreal x1, qreal y1, qreal x2, qreal y2 )
{
	startPoint=QPointF(x1,y1);
	endPoint=QPointF(x2,y2);
}
 
void LineItem::paint( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget /* = 0 */ )
{
	/*painter->setPen(QPen(Qt::green, 3, Qt::DashDotLine, Qt::RoundCap, Qt::RoundJoin));
	painter->drawRect(startPoint.x()-2,startPoint.y(),4,4);*/
	//painter->drawPoint(startPoint);
	//painter->drawPoint(endPoint);
	//painter->drawPoint(centerPoint);
 
	painter->setPen(Qt::blue);
	painter->setFont(QFont("Arial", 30));
	painter->drawText(QRectF(startPoint,endPoint), Qt::AlignCenter, "Qt");
 
}

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use QGraphicsScene addItem method, this method will add your item to scene and make it visible on your QGraphicsView.

Code:

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QGraphicsView *view = new QGraphicsView();
// set the view rect
 
QGraphicsScene *scene = new QGraphicsScene();
 
// Set the scene Rect
// scene->setSceneRect(0, 0, 400, 400);
 
view->setScene(scene);
 
LineItem *L1 = new LineItem();
L1->setLine(0, 0, 100, 100);
 
scene->addItem(L1);

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If this will not solve your problem then paste your code where you add LineItem to scene.

i have added it to view,but it did't show on the view

Code:

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#ifndef FILLVIEW_H
#define FILLVIEW_H
 
#include <QGraphicsView>
 #include <QGraphicsEllipseItem>
#include <QGraphicsLineItem>
#include "GraphicsItem/LineItem.h"
 enum ShapeName{
	Line,      //线(并非利用贝塞尔曲线绘制而成)
	Rectangle,   //矩形 
	Circle,      //æ ‡å‡†åœ†
	Triangle,    //三角形
	Ellipse,     //æ¤*圆
	BezierCurve, //贝塞尔曲线
	Control      //控制
};
 
 
class FillView : public QGraphicsView
{
	Q_OBJECT
 
public:
	FillView(QWidget *parent);
	~FillView();
 
 
 
	QPainter* ItemPainter;
 
		void mouseMoveEvent ( QMouseEvent * event ) ;
		void mouseReleaseEvent ( QMouseEvent * event );
		void mousePressEvent ( QMouseEvent * event ) ;
		void wheelEvent ( QWheelEvent * event ) ;
 
 
		QString getDrawingType()
		{
			return drawingType;
		};
		void ShowBackGroundGrid(bool show)
		{
			 BackGroundGridVisible=show	;
		}
 
		bool GetBackGroundVisble()
		{
			return BackGroundGridVisible;
		}
 
 
		public slots:
			 void setCurrentShape(ShapeName s);
		  signals:
			void getXY(float x,float y);
private:
	void scaledBy(double factor);
	QString	drawingType;
	QPointF beginPoint;
	QPointF endPoint;
	bool BackGroundGridVisible;
	QGraphicsLineItem* line;
	LineItem *ll;
	QGraphicsEllipseItem *circle;
	ShapeName currentShapeName;
 
 
public:
 
 
 
 
 
 
 
};
 
 
 
 
#endif // FILLVIEW_H

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Code:

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#include "fillview.h"
#include <QDebug>
#include <QTime>
 #include <QMouseEvent>
 #include <QGraphicsEllipseItem>
 
FillView::FillView(QWidget *parent)
	: QGraphicsView(parent)
{
	this->setDragMode(QGraphicsView::DragMode::RubberBandDrag);
	setMouseTracking(true);
 
	setRenderHints(QPainter::Antialiasing
		| QPainter::TextAntialiasing);
	setContextMenuPolicy(Qt::ActionsContextMenu);
	 line=new QGraphicsLineItem(beginPoint.x(),beginPoint.y(),beginPoint.x(),beginPoint.y()	);
 
 
//	scene()->addItem(&item);
}
 
 
FillView::~FillView()
{
 
}
 
void FillView::setCurrentShape(ShapeName s)
{
	  currentShapeName=s;
	  if (s!=ShapeName::Control)
	  {
		   this->setCursor(Qt::CrossCursor);
	  }else
	  {
		  this->setCursor(Qt::CursorShape::ArrowCursor);
	  }
 
 
}
 
void FillView::mousePressEvent( QMouseEvent * event )
{
	 beginPoint=mapToScene(event->pos());
//	 BoundaryPoint(beginPoint.toPoint());
	 switch(currentShapeName)
	 {
 
	 case ShapeName::Line:
		   {
			   ll=new LineItem(beginPoint.x(),beginPoint.y(),beginPoint.x(),beginPoint.y()	);
			  ll->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemIsFocusable);
			   scene()->addItem(line);
			   break;
		   }
	 case  ShapeName::Circle:
		 {
			 circle=new QGraphicsEllipseItem(beginPoint.x(),beginPoint.y(),0,0);
			 circle->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemIsFocusable);
 
			 scene()->addItem(circle);
			 break;
		 }
	 }
 
 
}
void FillView::mouseReleaseEvent(QMouseEvent * event)
{
 
	endPoint=mapToScene( event->pos());
	// BoundaryPoint(endPoint.toPoint());
	 switch(currentShapeName)
	 {
 
	 case ShapeName::Line:
		   {
			   ll->setLine(beginPoint.x(),beginPoint.y(),endPoint.x(),endPoint.y());
			   break;
		   }
	 case  ShapeName::Circle:
		 {
			 double x = this->endPoint.x() - this->beginPoint.x();
			 double y = this->endPoint.y() - this->beginPoint.y();
 
			 double radius = sqrt(x * x + y * y);
			 circle->setRect(this->beginPoint.x() -radius,
				 this->beginPoint.y() - radius,radius*2,radius*2);
			 break;
		 }
	 }
 
 
 
 
}
void FillView::mouseMoveEvent ( QMouseEvent * mevent ) 
{
 
	if (mevent->buttons()==Qt::LeftButton )
	{
		endPoint=mapToScene(mevent->pos());
		// BoundaryPoint(endPoint.toPoint());
 
		 switch(currentShapeName)
	 {
 
	 case ShapeName::Line:
		   {
			 ll->setLine(beginPoint.x(),beginPoint.y(),endPoint.x(),endPoint.y());
			   break;
		   }
	 case  ShapeName::Circle:
		 {
			 double x = this->endPoint.x() - this->beginPoint.x();
			 double y = this->endPoint.y() - this->beginPoint.y();
 
			 double radius = sqrt(x * x + y * y);
			 circle->setRect(this->beginPoint.x() -radius,
				 this->beginPoint.y() - radius,radius*2,radius*2);
			 break;
		 }
	 }
	}
 
 
	//qDebug() <<"X:"<<mevent->pos().x()<<"Y:"<<mevent->pos().y()<<QTime::currentTime().toString()	;
  QPointF pos=mapToScene(QPoint(mevent->pos().x(),mevent->pos().y()));
  if (this->scene()->sceneRect().contains(pos))
  {
	  emit getXY(pos.x(),pos.y());
	 // setCursor(Qt::CursorShape::ArrowCursor);
  }
  else
  {
	  QPointF posn=pos;
	  if (posn.x()>sceneRect().width())
	  {
		  posn.setX(sceneRect().width());
	  }
	  if (posn.y()>sceneRect().height())
	  {
		  posn.setY(sceneRect().height());
	  }
 
	  if (posn.x()<0)
	  {
		  posn.setX(0);
	  }
	  if (posn.y()<0)
	  {
		  posn.setY(0);
	  }
	  emit getXY(posn.x(),posn.y());
	  //setCursor(Qt::CursorShape::ForbiddenCursor);
  }
 
 
  if (mevent->buttons()==Qt::LeftButton)
  {
	  endPoint=mapToScene(mevent->pos());
	  QRectF rect(beginPoint,endPoint); 
 
  }
 
}
 
void FillView::wheelEvent( QWheelEvent * e )
{
	if (e->modifiers().testFlag(Qt::ControlModifier)){ // zoom only when CTRL key pressed
 
		int numSteps = e->delta() / 15 / 8;
 
		if (numSteps == 0) {
			e->ignore();
			return;
		}
		qreal sc = pow(1.25, numSteps); // I use scale factor 1.25
		this->scale(sc,sc);
 
 
		e->accept();
	}
}
 
void FillView::scaledBy(double factor)
{
 
}

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Added after 1 33 minutes:

thank you ,i goti it

ur scene() ins still empty ..
use like this

Code:

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QRectF sceneRect( preferred Geometry)
 
QGraphicsScene *scene = new QGraphicsScene(sceneRect);
 
addScene(scene);

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