diagramitem.cpp Example File

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 #include <QtWidgets>

 #include "diagramitem.h"
 #include "arrow.h"

 DiagramItem::DiagramItem(DiagramType diagramType, QMenu *contextMenu,
              QGraphicsItem *parent, QGraphicsScene *scene)
     : QGraphicsPolygonItem(parent, scene)
 {
     myDiagramType = diagramType;
     myContextMenu = contextMenu;

     QPainterPath path;
     switch (myDiagramType) {
         case StartEnd:
             path.moveTo(200, 50);
             path.arcTo(150, 0, 50, 50, 0, 90);
             path.arcTo(50, 0, 50, 50, 90, 90);
             path.arcTo(50, 50, 50, 50, 180, 90);
             path.arcTo(150, 50, 50, 50, 270, 90);
             path.lineTo(200, 25);
             myPolygon = path.toFillPolygon();
             break;
         case Conditional:
             myPolygon << QPointF(-100, 0) << QPointF(0, 100)
                       << QPointF(100, 0) << QPointF(0, -100)
                       << QPointF(-100, 0);
             break;
         case Step:
             myPolygon << QPointF(-100, -100) << QPointF(100, -100)
                       << QPointF(100, 100) << QPointF(-100, 100)
                       << QPointF(-100, -100);
             break;
         default:
             myPolygon << QPointF(-120, -80) << QPointF(-70, 80)
                       << QPointF(120, 80) << QPointF(70, -80)
                       << QPointF(-120, -80);
             break;
     }
     setPolygon(myPolygon);
     setFlag(QGraphicsItem::ItemIsMovable, true);
     setFlag(QGraphicsItem::ItemIsSelectable, true);
     setFlag(QGraphicsItem::ItemSendsGeometryChanges, true);
 }

 void DiagramItem::removeArrow(Arrow *arrow)
 {
     int index = arrows.indexOf(arrow);

     if (index != -1)
         arrows.removeAt(index);
 }

 void DiagramItem::removeArrows()
 {
     foreach (Arrow *arrow, arrows) {
         arrow->startItem()->removeArrow(arrow);
         arrow->endItem()->removeArrow(arrow);
         scene()->removeItem(arrow);
         delete arrow;
     }
 }

 void DiagramItem::addArrow(Arrow *arrow)
 {
     arrows.append(arrow);
 }

 QPixmap DiagramItem::image() const
 {
     QPixmap pixmap(250, 250);
     pixmap.fill(Qt::transparent);
     QPainter painter(&pixmap);
     painter.setPen(QPen(Qt::black, 8));
     painter.translate(125, 125);
     painter.drawPolyline(myPolygon);

     return pixmap;
 }

 void DiagramItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
 {
     scene()->clearSelection();
     setSelected(true);
     myContextMenu->exec(event->screenPos());
 }

 QVariant DiagramItem::itemChange(GraphicsItemChange change,
                      const QVariant &value)
 {
     if (change == QGraphicsItem::ItemPositionChange) {
         foreach (Arrow *arrow, arrows) {
             arrow->updatePosition();
         }
     }

     return value;
 }