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