title: PyQtGraph Custom PlotDataItem is not receiving mouseDragEvents
body: <p>I'm setting up a custom PlotDataItem to recieve mouseDragEvents. I've adjusted <a href="https://stackoverflow.com/questions/22448229/pyqtgraph-how-to-drag-a-a-plot-item">this answer</a> to my needs. For now I've just added a simple setData to the event to check if it's working. The custom PlotDataItem is as:</p>
  
  <pre><code>class CustomPlotItem(pg.PlotDataItem):
      def __init__(self, *args, **kargs):
          super().__init__(*args, **kargs)
  
      def setParentItem(self, parent):
          super().setParentItem(parent)
          self.parentBox = self.parentItem().parentItem()      
  
      def mouseDragEvent(self, ev):
          if ev.button() != QtCore.Qt.LeftButton:
              ev.ignore()
              return
  
          if ev.isStart():
              if self.parentBox.curveDragged != None or not self.mouseShape().contains(ev.pos()):
                  ev.ignore()
                  return
              self.parentBox.curveDragged = self            
          elif ev.isFinish():
              self.parentBox.curveDragged = None
              return
          elif self.parentBox.curveDragged != self:
              ev.ignore()
              return
  
          self.setData([40,50,60,200],[20,50,80,500])
          ev.accept()
  </code></pre>
  
  <p>The PlotDataItem is added to a custom ViewBox this implements <em>curveDragged</em>, so I know which curve is being dragged, if any. I've also disabled the ViewBox's mouseDragEvents for debugging purposes.</p>
  
  <p>However when try to drag the line in the ViewBox, nothing happens. Also if I add an exception at the top of the mouseDragEvent nothing happens. This leads me to believe mouseDragEvent is not being called at all. </p>
  
  <p>Im using Python 3.3 (Anaconda Distribution) and the develop version (0.9.9) of pyqtgraph.</p>
  
  <p>I hope someone can help me with this :). Thanks in advance.</p>