code: def trackerItem( self ):
          
          # check for the tracking enabled state
          if not self.isTrackingEnabled():
              return None
          
          # generate a new tracker item
          if not (self._trackerItem and self._trackerItem()):
              item = XChartTrackerItem()
              self.addItem(item)
              self._trackerItem = weakref.ref(item)
          
          return self._trackerItem()
docs: Returns the tracker item for this chart.
          
          :return     <XChartTrackerItem> || None