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         SINGLE_SOURCE = True
  34
  35         def __init__(self):
  36                 self.downstream_elements = CList()
  37                 self.master = None
  38                 self.sources = [ ]
  39                 self.source = None
  40                 self.__suspended = True
  41                 self.cache = None
  42
  43         def connectDownstream(self, downstream):
  44                 self.downstream_elements.append(downstream)
  45                 if self.master is None:
  46                         self.master = downstream
  47
  48         def connectUpstream(self, upstream):
  49                 assert not self.SINGLE_SOURCE or self.source is None
  50                 self.sources.append(upstream)
  51                 # self.source always refers to the last recent source added.
  52                 self.source = upstream
  53                 self.changed((self.CHANGED_DEFAULT,))
  54
  55         def connect(self, upstream):
  56                 self.connectUpstream(upstream)
  57                 upstream.connectDownstream(self)
  58
  59         # we disconnect from down to up
  60         def disconnectAll(self):
  61                 # we should not disconnect from upstream if
  62                 # there are still elements depending on us.
  63                 assert len(self.downstream_elements) == 0, "there are still downstream elements left"
  64
  65                 # Sources don't have a source themselves. don't do anything here.
  66                 for s in self.sources:
  67                         s.disconnectDownstream(self)
  68
  69                 if self.source:
  70                         # sources are owned by the Screen, so don't destroy them here.
  71                         self.destroy()
  72                 self.source = None
  73                 self.sources = [ ]
  74
  75         def disconnectDownstream(self, downstream):
  76                 self.downstream_elements.remove(downstream)
  77                 if self.master == downstream:
  78                         self.master = None
  79
  80                 if len(self.downstream_elements) == 0:
  81                         self.disconnectAll()
  82
  83         # default action: push downstream
  84         def changed(self, *args, **kwargs):
  85                 self.cache = { }
  86                 self.downstream_elements.changed(*args, **kwargs)
  87                 self.cache = None
  88
  89         def setSuspend(self, suspended):
  90                 changed = self.__suspended != suspended
  91                 if not self.__suspended and suspended:
  92                         self.doSuspend(1)
  93                 elif self.__suspended and not suspended:
  94                         self.doSuspend(0)
  95
  96                 self.__suspended = suspended
  97                 if changed:
  98                         for s in self.sources:
  99                                 s.checkSuspend()
 100
 101         suspended = property(lambda self: self.__suspended, setSuspend)
 102
 103         def checkSuspend(self):
 104                 self.suspended = reduce(lambda x, y: x and y.__suspended, self.downstream_elements, True)
 105
 106         def doSuspend(self, suspend):
 107                 pass
 108
 109         def destroy(self):
 110                 pass