callout.h Example File

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  #ifndef CALLOUT_H
  #define CALLOUT_H

  #include <QtCharts/QChartGlobal>
  #include <QtWidgets/QGraphicsItem>
  #include <QtGui/QFont>

  class QGraphicsSceneMouseEvent;

  QT_CHARTS_BEGIN_NAMESPACE
  class QChart;
  QT_CHARTS_END_NAMESPACE

  QT_CHARTS_USE_NAMESPACE

  class Callout : public QGraphicsItem
  {
  public:
      Callout(QChart *parent);

      void setText(const QString &text);
      void setAnchor(QPointF point);
      void updateGeometry();

      QRectF boundingRect() const;
      void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget);

  protected:
      void mousePressEvent(QGraphicsSceneMouseEvent *event);
      void mouseMoveEvent(QGraphicsSceneMouseEvent *event);

  private:
      QString m_text;
      QRectF m_textRect;
      QRectF m_rect;
      QPointF m_anchor;
      QFont m_font;
      QChart *m_chart;
  };

  #endif // CALLOUT_H