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         CHANGED_DEFAULT = 0   # initial "pull" state
   9         CHANGED_ALL = 1       # really everything changed
  10         CHANGED_CLEAR = 2     # we're expecting a real update soon. don't bother polling NOW, but clear data.
  11         CHANGED_SPECIFIC = 3  # second tuple will specify what exactly changed
  12         CHANGED_POLL = 4      # a timer expired
  13
  14         def __init__(self):
  15                 self.downstream_elements = CList()
  16                 self.master = None
  17                 self.source = None
  18                 self.clearCache()
  19
  20         def connectDownstream(self, downstream):
  21                 self.downstream_elements.append(downstream)
  22                 if self.master is None:
  23                         self.master = downstream
  24
  25         def connectUpstream(self, upstream):
  26                 assert self.source is None
  27                 self.source = upstream
  28                 self.changed((self.CHANGED_DEFAULT,))
  29
  30         def connect(self, upstream):
  31                 self.connectUpstream(upstream)
  32                 upstream.connectDownstream(self)
  33
  34         # we disconnect from down to up
  35         def disconnectAll(self):
  36                 # we should not disconnect from upstream if
  37                 # there are still elements depending on us.
  38                 assert len(self.downstream_elements) == 0, "there are still downstream elements left"
  39
  40                 # Sources don't have a source themselves. don't do anything here.
  41                 if self.source is not None:
  42                         self.source.disconnectDownstream(self)
  43
  44         def disconnectDownstream(self, downstream):
  45                 self.downstream_elements.remove(downstream)
  46                 if self.master == downstream:
  47                         self.master = None
  48
  49                 if len(self.downstream_elements) == 0:
  50                         self.disconnectAll()
  51
  52         # default action: push downstream
  53         def changed(self, *args, **kwargs):
  54                 self.clearCache()
  55                 self.downstream_elements.changed(*args, **kwargs)
  56                 self.clearCache()
  57
  58         def reconnectUpstream(self, new_upstream):
  59                 assert self.source is not None
  60                 self.source = new_upstream
  61
  62         def clearCache(self):
  63                 self.cache = None