lib/python/Components/Element.py

   1 from Tools.CList import CList
   2
   3 # down                       up
   4 # Render Converter Converter Source
   5
   6 # a bidirectional connection
   7 class Element:
   8         def __init__(self):
   9                 self.downstream_elements = CList()
  10                 self.upstream_elements = CList()
  11                 self.master = None
  12                 self.source = None
  13
  14         def connectDownstream(self, downstream):
  15                 self.downstream_elements.append(downstream)
  16                 if self.master is None:
  17                         self.master = downstream
  18
  19         def connectUpstream(self, upstream):
  20                 self.upstream_elements.append(upstream)
  21                 self.source = upstream # for single-source elements (i.e., most of them.)
  22                 self.changed()
  23
  24         def connect(self, upstream):
  25                 self.connectUpstream(upstream)
  26                 upstream.connectDownstream(self)
  27
  28         # we disconnect from down to up
  29         def disconnectAll(self):
  30                 # we should not disconnect from upstream if
  31                 # there are still elements depending on us.
  32                 assert len(self.downstream_elements) == 0, "there are still downstream elements left"
  33
  34                 # disconnect all upstream elements from us
  35                 for upstream in self.upstream_elements:
  36                         upstream.disconnectDownstream(self)
  37
  38         def disconnectDownstream(self, downstream):
  39                 self.downstream_elements.remove(downstream)
  40                 if self.master == downstream:
  41                         self.master = None
  42
  43                 if len(self.downstream_elements) == 0:
  44                         self.disconnectAll()
  45
  46         # default action: push downstream
  47         def changed(self, *args, **kwargs):
  48                 self.downstream_elements.changed(*args, **kwargs)