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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);
CHECK(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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