xpcom/ds/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 "nsTObserverArray.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  public:
  25   virtual ~Observer() = default;
  26   virtual void Notify(const T& aParam) = 0;
  27 };
  28
  29 /**
  30  * ObserverList<T> tracks Observer<T> and can notify them when Broadcast() is
  31  * called.
  32  * T represents the type of the object passed in argument to Broadcast() and
  33  * sent to Observer<T> objects through Notify().
  34  *
  35  * @see Observer.
  36  */
  37 template <class T>
  38 class ObserverList {
  39  public:
  40   /**
  41    * Note: When calling AddObserver, it's up to the caller to make sure the
  42    * object isn't going to be release as long as RemoveObserver hasn't been
  43    * called.
  44    *
  45    * @see RemoveObserver()
  46    */
  47   void AddObserver(Observer<T>* aObserver) {
  48     mObservers.AppendElementUnlessExists(aObserver);
  49   }
  50
  51   /**
  52    * Remove the observer from the observer list.
  53    * @return Whether the observer has been found in the list.
  54    */
  55   bool RemoveObserver(Observer<T>* aObserver) {
  56     return mObservers.RemoveElement(aObserver);
  57   }
  58
  59   uint32_t Length() { return mObservers.Length(); }
  60
  61   /**
  62    * Call Notify() on each item in the list.
  63    */
  64   void Broadcast(const T& aParam) {
  65     for (Observer<T>* obs : mObservers.ForwardRange()) {
  66       obs->Notify(aParam);
  67     }
  68   }
  69
  70  protected:
  71   nsTObserverArray<Observer<T>*> mObservers;
  72 };
  73
  74 }  // namespace mozilla
  75
  76 #endif  // mozilla_Observer_h