ash/shelf/scoped_observer_with_duplicated_sources.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef ASH_SHELF_SCOPED_OBSERVER_WITH_DUPLICATED_SOURCES_H_
   6 #define ASH_SHELF_SCOPED_OBSERVER_WITH_DUPLICATED_SOURCES_H_
   7
   8 #include <map>
   9
  10 #include "base/basictypes.h"
  11 #include "base/logging.h"
  12
  13 // ScopedObserverWithDuplicatedSources is used to keep track of the set of
  14 // sources an object has attached itself to as an observer. When
  15 // ScopedObserverWithDuplicatedSources is destroyed it removes the object as an
  16 // observer from all sources it has been added to.
  17 // ScopedObserverWithDuplicatedSources adds |observer| once for a particular
  18 // source, no matter how many times Add() is invoked. Additionaly |observer| is
  19 // only removed once Remove() is invoked the same number of times as Add().
  20
  21 template <class Source, class Observer>
  22 class ScopedObserverWithDuplicatedSources {
  23  public:
  24   explicit ScopedObserverWithDuplicatedSources(Observer* observer)
  25       : observer_(observer) {}
  26
  27   ~ScopedObserverWithDuplicatedSources() {
  28     typename SourceToAddCountMap::const_iterator iter =
  29         counted_sources_.begin();
  30     for (; iter != counted_sources_.end(); ++iter)
  31       iter->first->RemoveObserver(observer_);
  32   }
  33
  34   // Adds the object passed to the constructor only once as an observer on
  35   // |source|.
  36   void Add(Source* source) {
  37     if (counted_sources_.find(source) == counted_sources_.end())
  38       source->AddObserver(observer_);
  39     counted_sources_[source]++;
  40   }
  41
  42   // Only remove the object passed to the constructor as an observer from
  43   // |source| when Remove() is invoked the same number of times as Add().
  44   void Remove(Source* source) {
  45     typename SourceToAddCountMap::iterator iter =
  46         counted_sources_.find(source);
  47     DCHECK(iter != counted_sources_.end() && iter->second > 0);
  48
  49     if (--iter->second == 0) {
  50       counted_sources_.erase(source);
  51       source->RemoveObserver(observer_);
  52     }
  53   }
  54
  55   bool IsObserving(Source* source) const {
  56     return counted_sources_.find(source) != counted_sources_.end();
  57   }
  58
  59  private:
  60   typedef std::map<Source*, int> SourceToAddCountMap;
  61
  62   Observer* observer_;
  63
  64   // Map Source and its adding count.
  65   std::map<Source*, int> counted_sources_;
  66
  67   DISALLOW_COPY_AND_ASSIGN(ScopedObserverWithDuplicatedSources);
  68 };
  69
  70 #endif  // ASH_SHELF_SCOPED_OBSERVER_WITH_DUPLICATED_SOURCES_H_