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- // Copyright 2020 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_MULTI_SOURCE_OBSERVATION_H_
- #define BASE_SCOPED_MULTI_SOURCE_OBSERVATION_H_
- #include <stddef.h>
- #include <vector>
- #include "base/check.h"
- #include "base/containers/contains.h"
- #include "base/memory/raw_ptr.h"
- #include "base/ranges/algorithm.h"
- namespace base {
- // ScopedMultiSourceObservation is used to keep track of plural observation,
- // e.g. where an observer observes more than a single source.
- //
- // Use base::ScopedObservation for objects that observe only a single source.
- //
- // When ScopedMultiSourceObservation 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:
- // ScopedMultiSourceObservation<Foo, FooObserver> foo_observations_{this};
- // };
- //
- // MyFooObserver::OnFooCreated(Foo* foo) {
- // foo_observations_.AddObservation(foo);
- // }
- //
- // For cases with methods not named AddObserver/RemoveObserver:
- //
- // class MyFooStateObserver : public FooStateObserver {
- // ...
- // private:
- // ScopedMultiSourceObservation<Foo,
- // FooStateObserver,
- // &Foo::AddStateObserver,
- // &Foo::RemoveStateObserver>
- // foo_observations_{this};
- // };
- template <class Source,
- class Observer,
- void (Source::*AddObsFn)(Observer*) = &Source::AddObserver,
- void (Source::*RemoveObsFn)(Observer*) = &Source::RemoveObserver>
- class ScopedMultiSourceObservation {
- public:
- explicit ScopedMultiSourceObservation(Observer* observer)
- : observer_(observer) {}
- ScopedMultiSourceObservation(const ScopedMultiSourceObservation&) = delete;
- ScopedMultiSourceObservation& operator=(const ScopedMultiSourceObservation&) =
- delete;
- ~ScopedMultiSourceObservation() { RemoveAllObservations(); }
- // Adds the object passed to the constructor as an observer on |source|.
- void AddObservation(Source* source) {
- sources_.push_back(source);
- (source->*AddObsFn)(observer_);
- }
- // Remove the object passed to the constructor as an observer from |source|.
- void RemoveObservation(Source* source) {
- auto it = base::ranges::find(sources_, source);
- DCHECK(it != sources_.end());
- sources_.erase(it);
- (source->*RemoveObsFn)(observer_);
- }
- // Remove the object passed to the constructor as an observer from all sources
- // it's observing.
- void RemoveAllObservations() {
- for (Source* source : sources_)
- (source->*RemoveObsFn)(observer_);
- sources_.clear();
- }
- // Returns true if any source is being observed.
- bool IsObservingAnySource() const { return !sources_.empty(); }
- // Returns true if |source| is being observed.
- bool IsObservingSource(Source* source) const {
- DCHECK(source);
- return base::Contains(sources_, source);
- }
- // Returns the number of sources being observed.
- size_t GetSourcesCount() const { return sources_.size(); }
- private:
- const raw_ptr<Observer> observer_;
- std::vector<Source*> sources_;
- };
- } // namespace base
- #endif // BASE_SCOPED_MULTI_SOURCE_OBSERVATION_H_
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