Starts dragging information from this chart widget based on the
        dragData associated with this item.

def startDrag(self, data):
        """
        Starts dragging information from this chart widget based on the
        dragData associated with this item.
        """
        if not data:
            return
        
        widget = self.scene().chartWidget()
        drag = QDrag(widget)
        drag.setMimeData(data)
        drag.exec_()