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.
// Basic example (as a member variable):
//
//   class MyFooObserver : public FooObserver {
//     ...
//    private:
//     ScopedObserver<Foo, FooObserver> observed_foo_{this};
//   };
//
// For cases with methods not named AddObserver/RemoveObserver:
//
//   class MyFooStateObserver : public FooStateObserver {
//     ...
//    private:
//     ScopedObserver<Foo,
//                    FooStateObserver,
//                    &Foo::AddStateObserver,
//                    &Foo::RemoveStateObserver>
//       observed_foo_{this};
//   };
template <class Source,
          class Observer,
          void (Source::*AddObsFn)(Observer*) = &Source::AddObserver,
          void (Source::*RemoveObsFn)(Observer*) = &Source::RemoveObserver>
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->*AddObsFn)(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->*RemoveObsFn)(observer_);
  }

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

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

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

  size_t GetSourcesCount() const { return sources_.size(); }

 private:
  Observer* observer_;

  std::vector<Source*> sources_;

  DISALLOW_COPY_AND_ASSIGN(ScopedObserver);
};

#endif  // BASE_SCOPED_OBSERVER_H_