xpcom/glue/Observer.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_Observer_h
   8 #define mozilla_Observer_h
   9
  10 #include "nsTArray.h"
  11
  12 namespace mozilla {
  13
  14 /**
  15  * Observer<T> provides a way for a class to observe something.
  16  * When an event has to be broadcasted to all Observer<T>, Notify() method
  17  * is called.
  18  * T represents the type of the object passed in argument to Notify().
  19  *
  20  * @see ObserverList.
  21  */
  22 template<class T>
  23 class Observer
  24 {
  25 public:
  26   virtual ~Observer() {}
  27   virtual void Notify(const T& aParam) = 0;
  28 };
  29
  30 /**
  31  * ObserverList<T> tracks Observer<T> and can notify them when Broadcast() is
  32  * called.
  33  * T represents the type of the object passed in argument to Broadcast() and
  34  * sent to Observer<T> objects through Notify().
  35  *
  36  * @see Observer.
  37  */
  38 template<class T>
  39 class ObserverList
  40 {
  41 public:
  42   /**
  43    * Note: When calling AddObserver, it's up to the caller to make sure the
  44    * object isn't going to be release as long as RemoveObserver hasn't been
  45    * called.
  46    *
  47    * @see RemoveObserver()
  48    */
  49   void AddObserver(Observer<T>* aObserver)
  50   {
  51     mObservers.AppendElement(aObserver);
  52   }
  53
  54   /**
  55    * Remove the observer from the observer list.
  56    * @return Whether the observer has been found in the list.
  57    */
  58   bool RemoveObserver(Observer<T>* aObserver)
  59   {
  60     return mObservers.RemoveElement(aObserver);
  61   }
  62
  63   uint32_t Length()
  64   {
  65     return mObservers.Length();
  66   }
  67
  68   void Broadcast(const T& aParam)
  69   {
  70     uint32_t size = mObservers.Length();
  71     for (uint32_t i = 0; i < size; ++i) {
  72       mObservers[i]->Notify(aParam);
  73     }
  74   }
  75
  76 protected:
  77   nsTArray<Observer<T>*> mObservers;
  78 };
  79
  80 } // namespace mozilla
  81
  82 #endif // mozilla_Observer_h