base/scoped_observer.h

   1 // Copyright (c) 2012 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 BASE_SCOPED_OBSERVER_H_
   6 #define BASE_SCOPED_OBSERVER_H_
   7
   8 #include <algorithm>
   9 #include <vector>
  10
  11 #include "base/basictypes.h"
  12 #include "base/logging.h"
  13
  14 // ScopedObserver is used to keep track of the set of sources an object has
  15 // attached itself to as an observer. When ScopedObserver is destroyed it
  16 // removes the object as an observer from all sources it has been added to.
  17 template <class Source, class Observer>
  18 class ScopedObserver {
  19  public:
  20   explicit ScopedObserver(Observer* observer) : observer_(observer) {}
  21
  22   ~ScopedObserver() {
  23     RemoveAll();
  24   }
  25
  26   // Adds the object passed to the constructor as an observer on |source|.
  27   void Add(Source* source) {
  28     sources_.push_back(source);
  29     source->AddObserver(observer_);
  30   }
  31
  32   // Remove the object passed to the constructor as an observer from |source|.
  33   void Remove(Source* source) {
  34     auto it = std::find(sources_.begin(), sources_.end(), source);
  35     DCHECK(it != sources_.end());
  36     sources_.erase(it);
  37     source->RemoveObserver(observer_);
  38   }
  39
  40   void RemoveAll() {
  41     for (size_t i = 0; i < sources_.size(); ++i)
  42       sources_[i]->RemoveObserver(observer_);
  43     sources_.clear();
  44   }
  45
  46   bool IsObserving(Source* source) const {
  47     return std::find(sources_.begin(), sources_.end(), source) !=
  48         sources_.end();
  49   }
  50
  51   bool IsObservingSources() const { return !sources_.empty(); }
  52
  53  private:
  54   Observer* observer_;
  55
  56   std::vector<Source*> sources_;
  57
  58   DISALLOW_COPY_AND_ASSIGN(ScopedObserver);
  59 };
  60
  61 #endif  // BASE_SCOPED_OBSERVER_H_