| // Copyright (c) 2011 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 <stddef.h> |
| |
| #include <algorithm> |
| #include <limits> |
| #include <vector> |
| |
| #include "base/logging.h" |
| #include "base/macros.h" |
| #include "base/memory/weak_ptr.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: |
| // base::ObserverList<Observer> observer_list_; |
| // }; |
| // |
| // |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| namespace base { |
| |
| template <class ObserverType> |
| class ObserverListBase |
| : public SupportsWeakPtr<ObserverListBase<ObserverType>> { |
| 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 |
| }; |
| |
| // An iterator class that can be used to access the list of observers. See |
| // also the FOR_EACH_OBSERVER macro defined below. |
| class Iterator { |
| public: |
| explicit Iterator(ObserverListBase<ObserverType>* list); |
| ~Iterator(); |
| ObserverType* GetNext(); |
| |
| private: |
| WeakPtr<ObserverListBase<ObserverType>> list_; |
| size_t index_; |
| size_t max_index_; |
| }; |
| |
| ObserverListBase() : notify_depth_(0), type_(NOTIFY_ALL) {} |
| explicit ObserverListBase(NotificationType type) |
| : notify_depth_(0), type_(type) {} |
| |
| // Add an observer to the list. An observer should not be added to |
| // the same list more than once. |
| void AddObserver(ObserverType* obs); |
| |
| // Remove an observer from the list if it is in the list. |
| void RemoveObserver(ObserverType* obs); |
| |
| // Determine whether a particular observer is in the list. |
| bool HasObserver(const ObserverType* observer) const; |
| |
| void Clear(); |
| |
| protected: |
| size_t size() const { return observers_.size(); } |
| |
| void Compact(); |
| |
| private: |
| typedef std::vector<ObserverType*> ListType; |
| |
| ListType observers_; |
| int notify_depth_; |
| NotificationType type_; |
| |
| friend class ObserverListBase::Iterator; |
| |
| DISALLOW_COPY_AND_ASSIGN(ObserverListBase); |
| }; |
| |
| template <class ObserverType> |
| ObserverListBase<ObserverType>::Iterator::Iterator( |
| ObserverListBase<ObserverType>* list) |
| : list_(list->AsWeakPtr()), |
| index_(0), |
| max_index_(list->type_ == NOTIFY_ALL ? std::numeric_limits<size_t>::max() |
| : list->observers_.size()) { |
| ++list_->notify_depth_; |
| } |
| |
| template <class ObserverType> |
| ObserverListBase<ObserverType>::Iterator::~Iterator() { |
| if (list_.get() && --list_->notify_depth_ == 0) |
| list_->Compact(); |
| } |
| |
| template <class ObserverType> |
| ObserverType* ObserverListBase<ObserverType>::Iterator::GetNext() { |
| if (!list_.get()) |
| return nullptr; |
| 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_++] : nullptr; |
| } |
| |
| template <class ObserverType> |
| void ObserverListBase<ObserverType>::AddObserver(ObserverType* obs) { |
| DCHECK(obs); |
| auto it = std::find(observers_.begin(), observers_.end(), obs); |
| if (it != observers_.end()) { |
| NOTREACHED() << "Observers can only be added once!"; |
| return; |
| } |
| observers_.push_back(obs); |
| } |
| |
| template <class ObserverType> |
| void ObserverListBase<ObserverType>::RemoveObserver(ObserverType* obs) { |
| DCHECK(obs); |
| typename ListType::iterator it = |
| std::find(observers_.begin(), observers_.end(), obs); |
| if (it != observers_.end()) { |
| if (notify_depth_) { |
| *it = nullptr; |
| } else { |
| observers_.erase(it); |
| } |
| } |
| } |
| |
| template <class ObserverType> |
| bool ObserverListBase<ObserverType>::HasObserver( |
| const ObserverType* observer) const { |
| for (size_t i = 0; i < observers_.size(); ++i) { |
| if (observers_[i] == observer) |
| return true; |
| } |
| return false; |
| } |
| |
| template <class ObserverType> |
| void ObserverListBase<ObserverType>::Clear() { |
| if (notify_depth_) { |
| for (typename ListType::iterator it = observers_.begin(); |
| it != observers_.end(); ++it) { |
| *it = nullptr; |
| } |
| } else { |
| observers_.clear(); |
| } |
| } |
| |
| template <class ObserverType> |
| void ObserverListBase<ObserverType>::Compact() { |
| observers_.erase( |
| std::remove(observers_.begin(), observers_.end(), nullptr), |
| observers_.end()); |
| } |
| |
| template <class ObserverType, bool check_empty = false> |
| class ObserverList : public ObserverListBase<ObserverType> { |
| public: |
| typedef typename ObserverListBase<ObserverType>::NotificationType |
| NotificationType; |
| |
| ObserverList() {} |
| explicit ObserverList(NotificationType type) |
| : ObserverListBase<ObserverType>(type) {} |
| |
| ~ObserverList() { |
| // When check_empty is true, assert that the list is empty on destruction. |
| if (check_empty) { |
| ObserverListBase<ObserverType>::Compact(); |
| DCHECK_EQ(ObserverListBase<ObserverType>::size(), 0U); |
| } |
| } |
| |
| bool might_have_observers() const { |
| return ObserverListBase<ObserverType>::size() != 0; |
| } |
| }; |
| |
| #define FOR_EACH_OBSERVER(ObserverType, observer_list, func) \ |
| do { \ |
| if ((observer_list).might_have_observers()) { \ |
| base::ObserverListBase<ObserverType>::Iterator it_inside_observer_macro( \ |
| &observer_list); \ |
| ObserverType* obs; \ |
| while ((obs = it_inside_observer_macro.GetNext()) != nullptr) \ |
| obs->func; \ |
| } \ |
| } while (0) |
| |
| } // namespace base |
| |
| #endif // BASE_OBSERVER_LIST_H_ |