michael@0: // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_OBSERVER_LIST_H__
michael@0: #define BASE_OBSERVER_LIST_H__
michael@0: 
michael@0: #include <algorithm>
michael@0: #include <limits>
michael@0: #include <vector>
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: #include "base/logging.h"
michael@0: 
michael@0: #if defined(ANDROID) && defined(_STLP_STD_NAME)
michael@0: using _STLP_STD_NAME::find;
michael@0: #endif
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: ///////////////////////////////////////////////////////////////////////////////
michael@0: //
michael@0: // OVERVIEW:
michael@0: //
michael@0: //   A container for a list of observers.  Unlike a normal STL vector or list,
michael@0: //   this container can be modified during iteration without invalidating the
michael@0: //   iterator.  So, it safely handles the case of an observer removing itself
michael@0: //   or other observers from the list while observers are being notified.
michael@0: //
michael@0: // TYPICAL USAGE:
michael@0: //
michael@0: //   class MyWidget {
michael@0: //    public:
michael@0: //     ...
michael@0: //
michael@0: //     class Observer {
michael@0: //      public:
michael@0: //       virtual void OnFoo(MyWidget* w) = 0;
michael@0: //       virtual void OnBar(MyWidget* w, int x, int y) = 0;
michael@0: //     };
michael@0: //
michael@0: //     void AddObserver(Observer* obs) {
michael@0: //       observer_list_.AddObserver(obs);
michael@0: //     }
michael@0: //
michael@0: //     void RemoveObserver(Observer* obs) {
michael@0: //       observer_list_.RemoveObserver(obs);
michael@0: //     }
michael@0: //
michael@0: //     void NotifyFoo() {
michael@0: //       FOR_EACH_OBSERVER(Observer, observer_list_, OnFoo(this));
michael@0: //     }
michael@0: //
michael@0: //     void NotifyBar(int x, int y) {
michael@0: //       FOR_EACH_OBSERVER(Observer, observer_list_, OnBar(this, x, y));
michael@0: //     }
michael@0: //
michael@0: //    private:
michael@0: //     ObserverList<Observer> observer_list_;
michael@0: //   };
michael@0: //
michael@0: //
michael@0: ///////////////////////////////////////////////////////////////////////////////
michael@0: 
michael@0: template <class ObserverType, bool check_empty = false>
michael@0: class ObserverList {
michael@0:  public:
michael@0:   // Enumeration of which observers are notified.
michael@0:   enum NotificationType {
michael@0:     // Specifies that any observers added during notification are notified.
michael@0:     // This is the default type if non type is provided to the constructor.
michael@0:     NOTIFY_ALL,
michael@0: 
michael@0:     // Specifies that observers added while sending out notification are not
michael@0:     // notified.
michael@0:     NOTIFY_EXISTING_ONLY
michael@0:   };
michael@0: 
michael@0:   ObserverList() : notify_depth_(0), type_(NOTIFY_ALL) {}
michael@0:   ObserverList(NotificationType type) : notify_depth_(0), type_(type) {}
michael@0:   ~ObserverList() {
michael@0:     // When check_empty is true, assert that the list is empty on destruction.
michael@0:     if (check_empty) {
michael@0:       Compact();
michael@0:       DCHECK_EQ(observers_.size(), 0U);
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   // Add an observer to the list.
michael@0:   void AddObserver(ObserverType* obs) {
michael@0:     DCHECK(find(observers_.begin(), observers_.end(), obs) == observers_.end())
michael@0:         << "Observers can only be added once!";
michael@0:     observers_.push_back(obs);
michael@0:   }
michael@0: 
michael@0:   // Remove an observer from the list.
michael@0:   void RemoveObserver(ObserverType* obs) {
michael@0:     typename ListType::iterator it =
michael@0:       std::find(observers_.begin(), observers_.end(), obs);
michael@0:     if (it != observers_.end()) {
michael@0:       if (notify_depth_) {
michael@0:         *it = 0;
michael@0:       } else {
michael@0:         observers_.erase(it);
michael@0:       }
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   size_t size() const {
michael@0:     return observers_.size();
michael@0:   }
michael@0: 
michael@0:   ObserverType* GetElementAt(int index) const {
michael@0:     return observers_[index];
michael@0:   }
michael@0: 
michael@0:   // An iterator class that can be used to access the list of observers.  See
michael@0:   // also the FOREACH_OBSERVER macro defined below.
michael@0:   class Iterator {
michael@0:    public:
michael@0:     Iterator(const ObserverList<ObserverType>& list)
michael@0:         : list_(list),
michael@0:           index_(0),
michael@0:           max_index_(list.type_ == NOTIFY_ALL ?
michael@0:                      std::numeric_limits<size_t>::max() :
michael@0:                      list.observers_.size()) {
michael@0:       ++list_.notify_depth_;
michael@0:     }
michael@0: 
michael@0:     ~Iterator() {
michael@0:       if (--list_.notify_depth_ == 0)
michael@0:         list_.Compact();
michael@0:     }
michael@0: 
michael@0:     ObserverType* GetNext() {
michael@0:       ListType& observers = list_.observers_;
michael@0:       // Advance if the current element is null
michael@0:       size_t max_index = std::min(max_index_, observers.size());
michael@0:       while (index_ < max_index && !observers[index_])
michael@0:         ++index_;
michael@0:       return index_ < max_index ? observers[index_++] : NULL;
michael@0:     }
michael@0: 
michael@0:    private:
michael@0:     const ObserverList<ObserverType>& list_;
michael@0:     size_t index_;
michael@0:     size_t max_index_;
michael@0:   };
michael@0: 
michael@0:  private:
michael@0:   typedef std::vector<ObserverType*> ListType;
michael@0: 
michael@0:   void Compact() const {
michael@0:     typename ListType::iterator it = observers_.begin();
michael@0:     while (it != observers_.end()) {
michael@0:       if (*it) {
michael@0:         ++it;
michael@0:       } else {
michael@0:         it = observers_.erase(it);
michael@0:       }
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   // These are marked mutable to facilitate having NotifyAll be const.
michael@0:   mutable ListType observers_;
michael@0:   mutable int notify_depth_;
michael@0:   NotificationType type_;
michael@0: 
michael@0:   friend class ObserverList::Iterator;
michael@0: 
michael@0:   DISALLOW_EVIL_CONSTRUCTORS(ObserverList);
michael@0: };
michael@0: 
michael@0: } // namespace base
michael@0: 
michael@0: #define FOR_EACH_OBSERVER(ObserverType, observer_list, func)		\
michael@0:   do {									\
michael@0:     base::ObserverList<ObserverType>::Iterator it(observer_list);	\
michael@0:     ObserverType* obs;							\
michael@0:     while ((obs = it.GetNext()) != NULL)				\
michael@0:       obs->func;							\
michael@0:   } while (0)
michael@0: 
michael@0: #endif  // BASE_OBSERVER_LIST_H__