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// 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 <vector>
#include <algorithm>
#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:
ObserverList() : notify_depth_(0) {}
~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);
}
}
}
// 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) {
++list_.notify_depth_;
}
~Iterator() {
if (--list_.notify_depth_ == 0)
list_.Compact();
}
ObserverType* GetNext() {
ListType& observers = list_.observers_;
// Advance if the current element is null
while (index_ < observers.size() && !observers[index_])
++index_;
return index_ < observers.size() ? observers[index_++] : NULL;
}
private:
const ObserverList<ObserverType>& list_;
size_t 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_;
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__
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