base/scoped_observer.h

// Copyright (c) 2012 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_SCOPED_OBSERVER_H_
#define BASE_SCOPED_OBSERVER_H_

#include <stddef.h>

#include <algorithm>
#include <vector>

#include "base/logging.h"
#include "base/macros.h"
#include "base/stl_util.h"

// ScopedObserver is used to keep track of the set of sources an object has
// attached itself to as an observer. When ScopedObserver is destroyed it
// removes the object as an observer from all sources it has been added to.
template <class Source, class Observer>
class ScopedObserver {
 public:
  explicit ScopedObserver(Observer* observer) : observer_(observer) {}

  ~ScopedObserver() {
    RemoveAll();
  }

  // Adds the object passed to the constructor as an observer on |source|.
  void Add(Source* source) {
    sources_.push_back(source);
    source->AddObserver(observer_);
  }

  // Remove the object passed to the constructor as an observer from |source|.
  void Remove(Source* source) {
    auto it = std::find(sources_.begin(), sources_.end(), source);
    DCHECK(it != sources_.end());
    sources_.erase(it);
    source->RemoveObserver(observer_);
  }

  void RemoveAll() {
    for (size_t i = 0; i < sources_.size(); ++i)
      sources_[i]->RemoveObserver(observer_);
    sources_.clear();
  }

  bool IsObserving(Source* source) const {
    return base::ContainsValue(sources_, source);
  }

  bool IsObservingSources() const { return !sources_.empty(); }

 private:
  Observer* observer_;

  std::vector<Source*> sources_;

  DISALLOW_COPY_AND_ASSIGN(ScopedObserver);
};

#endif  // BASE_SCOPED_OBSERVER_H_