Wed Dec 26 16:00:00 GMT 2001

Observer

#: util:Observer.py # Class support for "observer" pattern. from Synchronization import * class Observer: def update(observable, arg): '''Called when the observed object is modified. You call an Observable object's notifyObservers method to notify all the object's observers of the change.''' pass class Observable(Synchronization): def __init__(self): self.obs = [] self.changed = 0 Synchronization.__init__(self) def addObserver(self, observer): if observer not in self.obs: self.obs.append(observer) def deleteObserver(self, observer): self.obs.remove(observer) def notifyObservers(self, arg = None): '''If 'changed' indicates that this object has changed, notify all its observers, then call clearChanged(). Each observer has its update() called with two arguments: this observable object and the generic 'arg'.''' self.mutex.acquire() try: if not self.changed: return # Make a local copy in case of synchronous # additions of observers: localArray = self.obs[:] self.clearChanged() finally: self.mutex.release() # Updating is not required to be synchronized: for observer in localArray: observer.update(self, arg) def deleteObservers(self): self.obs = [] def setChanged(self): self.changed = 1 def clearChanged(self): self.changed = 0 def hasChanged(self): return self.changed def countObservers(self): return len(self.obs) synchronize(Observable, "addObserver deleteObserver deleteObservers " + "setChanged clearChanged hasChanged " + "countObservers") #:~


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