Changing mouse cursor in a QObject - QGraphicsItem

问题:

I would like to change my mouse cursor when it is in a graphics item (MyCircle inherits from QObject and QGraphicsItem). Had my class inherited from QWidget, I would have reimplemented enterEvent() and leaveEvent() and use it as follows :

MyCircle::MyCircle(QObject *parent)
    : QWidget(parent), QGraphicsItem() // But I can't
{
    rect = QRect(-100,-100,200,200);
    connect(this,SIGNAL(mouseEntered()),this,SLOT(in()));
    connect(this,SIGNAL(mouseLeft()),this,SLOT(out()));
}

void MyCircle::in()
{
    QApplication::setOverrideCursor(Qt::PointingHandCursor);
}

void MyCircle::out()
{
    QApplication::setOverrideCursor(Qt::ArrowCursor);
}

void MyCircle::enterEvent(QEvent *)
{
    emit mouseEntered();
}

void MyCircle::leaveEvent(QEvent *)
{
    emit mouseLeft();
}

Unfortunately, I need to animate that circle (it's a button actually), so I need QObject, is there an easy way to change the cursor ?

回答1:

You can probably use hover events.

In your class constructor make sure you do...

setAcceptHoverEvents(true);

Then override hoverEnterEvent and hoverLeaveEvent.

virtual void hoverEnterEvent (QGraphicsSceneHoverEvent *event) override
{
  QGraphicsItem::hoverEnterEvent(event);
  QApplication::setOverrideCursor(Qt::PointingHandCursor);
}

virtual void hoverLeaveEvent (QGraphicsSceneHoverEvent *event) override
{
  QGraphicsItem::hoverLeaveEvent(event);
  QApplication::setOverrideCursor(Qt::ArrowCursor);
}

As a side note: do you actually inherit from both QObject and QGraphicsItem? If so, you could probably achieve the same goal by simply inheriting from QGraphicsObject.

Edit 1: In answer to...

I have the pointing hand icone in my whole bounding rect, how can I reduce the area only to my drawing (in this case a circle) ?

Override QGraphicsItem::shape to return a QPainterPath representing the actual shape...

virtual QPainterPath shape () const override
{
  QPainterPath path;

  /*
   * Update path to represent the area in which you want
   * the mouse pointer to change.  This will probably be
   * based on the code in your 'paint' method.
   */
  return(path);
}

Now override QGraphicsItem::hoverMoveEvent to make use of the shape method...

virtual void hoverMoveEvent (QGraphicsSceneHoverEvent *event) override
{
  QGraphicsItem::hoverMoveEvent(event);
  if (shape().contains(event->pos())) {
    QApplication::setOverrideCursor(Qt::PointingHandCursor);
  } else {
    QApplication::setOverrideCursor(Qt::ArrowCursor);
  }
}

The above could, obviously, have an impact on performance depending on the complexity of the shape drawn and, hence, the QPainterPath.

(Note: rather than using QGraphicsItem::shape you could do a similar thing with QGraphicsItem::opaque instead.)

回答2:

QGraphicsItem already has a method for changing the cursor, so you don't need to manually play around with hover events:

QGraphicsItem::setCursor(const QCursor &cursor)

http://doc.qt.io/qt-5/qgraphicsitem.html#setCursor

PS: The dual inheritance of QWidget and QGraphicsItem you do is also a bad idea, only inherit from QGraphicsItem.