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
   8 def cached(f):
   9         name = f.__name__
  10         def wrapper(self):
  11                 cache = self.cache
  12                 if cache is None:
  13                         return f(self)
  14                 if name not in cache:
  15                         cache[name] = (True, f(self))
  16                 return cache[name][1]
  17         return wrapper
  18
  19 class ElementError(Exception):
  20     def __init__(self, message):
  21         self.msg = message
  22
  23     def __str__(self):
  24         return self.msg
  25
  26 class Element(object):
  27         CHANGED_DEFAULT = 0   # initial "pull" state
  28         CHANGED_ALL = 1       # really everything changed
  29         CHANGED_CLEAR = 2     # we're expecting a real update soon. don't bother polling NOW, but clear data.
  30         CHANGED_SPECIFIC = 3  # second tuple will specify what exactly changed
  31         CHANGED_POLL = 4      # a timer expired
  32
  33         def __init__(self):
  34                 self.downstream_elements = CList()
  35                 self.master = None
  36                 self.source = None
  37                 self.__suspended = True
  38                 self.cache = None
  39
  40         def connectDownstream(self, downstream):
  41                 self.downstream_elements.append(downstream)
  42                 if self.master is None:
  43                         self.master = downstream
  44
  45         def connectUpstream(self, upstream):
  46                 assert self.source is None
  47                 self.source = upstream
  48                 self.changed((self.CHANGED_DEFAULT,))
  49
  50         def connect(self, upstream):
  51                 self.connectUpstream(upstream)
  52                 upstream.connectDownstream(self)
  53
  54         # we disconnect from down to up
  55         def disconnectAll(self):
  56                 # we should not disconnect from upstream if
  57                 # there are still elements depending on us.
  58                 assert len(self.downstream_elements) == 0, "there are still downstream elements left"
  59
  60                 # Sources don't have a source themselves. don't do anything here.
  61                 if self.source is not None:
  62                         self.source.disconnectDownstream(self)
  63                         # sources are owned by the Screen, so don't destroy them here.
  64                         self.destroy()
  65
  66         def disconnectDownstream(self, downstream):
  67                 self.downstream_elements.remove(downstream)
  68                 if self.master == downstream:
  69                         self.master = None
  70
  71                 if len(self.downstream_elements) == 0:
  72                         self.disconnectAll()
  73
  74         # default action: push downstream
  75         def changed(self, *args, **kwargs):
  76                 self.cache = { }
  77                 self.downstream_elements.changed(*args, **kwargs)
  78                 self.cache = None
  79
  80         def reconnectUpstream(self, new_upstream):
  81                 assert self.source is not None
  82                 self.source = new_upstream
  83
  84         def setSuspend(self, suspended):
  85                 changed = self.__suspended != suspended
  86                 if not self.__suspended and suspended:
  87                         self.doSuspend(1)
  88                 elif self.__suspended and not suspended:
  89                         self.doSuspend(0)
  90
  91                 self.__suspended = suspended
  92                 if self.source is not None and changed:
  93                         self.source.checkSuspend()
  94
  95         suspended = property(lambda self: self.__suspended, setSuspend)
  96
  97         def checkSuspend(self):
  98                 self.suspended = reduce(lambda x, y: x and y.__suspended, self.downstream_elements, True)
  99
 100         def doSuspend(self, suspend):
 101                 pass
 102
 103         def destroy(self):
 104                 pass