QCustomPlot鼠标拖拽游标

Question

我在y轴上添加了一个游标，想要通过鼠标来拖动游标在y轴上滑动

Answer 1

要实现在QCustomPlot上拖拽游标,可以这样做:

1. 定义游标类,继承QGraphicsItem

 cpp
 class Cursor : public QGraphicsItem
 {
 public:
     Cursor();
     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
 }; 

1. 重写sceneEvent方法,检测鼠标按下和移动事件

 cpp
 void Cursor::sceneEvent(QEvent *event)
 {
     switch (event->type()) {
     case QEvent::GraphicsSceneMousePress:
         mousePressPosition = static_cast<QGraphicsSceneMouseEvent*>(event)->pos();
         break;
     case QEvent::GraphicsSceneMouseMove: 
         if (static_cast<QGraphicsSceneMouseEvent*>(event)->buttons() & Qt::LeftButton) {
            // 拖动游标
            QPointF position = static_cast<QGraphicsSceneMouseEvent*>(event)->pos();
            setPos(mapToParent(position - mousePressPosition)); 
         }
         break;
     }
     QGraphicsItem::sceneEvent(event);
 }

1. 重写mouseReleaseEvent结束拖拽

 cpp
 void Cursor::sceneEvent(QEvent *event) 
 {
     if (event->type() == QEvent::GraphicsSceneMouseRelease) {
         // 结束拖拽
         mousePressPosition = QPointF(); 
     }
 }

1. 将游标添加到QCustomPlot的scene中

 cpp
 Cursor *cursor = new Cursor;
 customPlot->scene()->addItem(cursor);

1. 重写QCustomPlot的mousePressEvent/MoveEvent/ReleaseEvent,转发给游标

 cpp
 void QCustomPlot::mousePressEvent(QMouseEvent *event)
 {
     if (cursor)
         cursor->sceneEvent(event);
     QCustomPlot::mousePressEvent(event);
 }
 
 void QCustomPlot::mouseMoveEvent(QMouseEvent *event) 
 {
     if (cursor)
         cursor->sceneEvent(event);
     QCustomPlot::mouseMoveEvent(event);
 }
 
 void QCustomPlot::mouseReleaseEvent(QMouseEvent *event)
 {
     if (cursor) 
         cursor->sceneEvent(event);
     QCustomPlot::mouseReleaseEvent(event);
 }

这样,当用户在QCustomPlot上单击并拖动鼠标时,会触发游标的sceneEvent方法,从而实现游标的拖拽效果。

希望这个示例能帮助您实现QCustomPlot上拖拽游标的需求。如有任何其他问题,欢迎在评论中提出。