code: def dragDropFilter( self ):
          
          filt = None
          if ( self._dragDropFilterRef ):
              filt = self._dragDropFilterRef()
          
          if ( not filt ):
              self._dragDropFilterRef = None
          
          return filt
docs: Returns a drag and drop filter method.  If set, the method should \
          accept 2 arguments: a QWidget and a drag/drop event and process it.
          
          :usage      |from projexui.qt.QtCore import QEvent
                      |
                      |class MyWidget(QWidget):
                      |   def __init__( self, parent ):
                      |       super(MyWidget, self).__init__(parent)
                      |       
                      |       self._tree = XCalendarWidget(self)
                      |       self._tree.setDragDropFilter(MyWidget.handleDragDrop)
                      |   
                      |   @staticmethod
                      |   def handleDragDrop(object, event):
                      |       if ( event.type() == QEvent.DragEnter ):
                      |           event.acceptProposedActions()
                      |       elif ( event.type() == QEvent.Drop ):
                      |           print 'dropping'
          
          :return     <function> || <method> || None