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// Copyright 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#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(), 0);
}
}
// 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) {
ListType::iterator it = 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 {
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()) \
obs->func; \
} while (0)
#endif // BASE_OBSERVER_LIST_H__
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