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109 lines
3.5 KiB
C++
109 lines
3.5 KiB
C++
// Copyright 2020 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_SCOPED_MULTI_SOURCE_OBSERVATION_H_
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#define BASE_SCOPED_MULTI_SOURCE_OBSERVATION_H_
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#include <stddef.h>
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#include <vector>
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#include "base/check.h"
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#include "base/containers/contains.h"
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#include "base/memory/raw_ptr.h"
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#include "base/ranges/algorithm.h"
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#include "base/scoped_observation_traits.h"
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namespace base {
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// ScopedMultiSourceObservation is used to keep track of plural observation,
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// e.g. where an observer observes more than a single source.
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//
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// Use base::ScopedObservation for objects that observe only a single source.
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//
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// When ScopedMultiSourceObservation is destroyed, it removes the object as an
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// observer from all sources it has been added to.
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// Basic example (as a member variable):
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//
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// class MyFooObserver : public FooObserver {
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// ...
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// private:
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// ScopedMultiSourceObservation<Foo, FooObserver> foo_observations_{this};
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// };
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//
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// MyFooObserver::OnFooCreated(Foo* foo) {
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// foo_observations_.AddObservation(foo);
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// }
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//
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////////////////////////////////////////////////////////////////////////////////
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//
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// By default `ScopedMultiSourceObservation` only works with sources that expose
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// `AddObserver` and `RemoveObserver`. However, it's also possible to
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// adapt it to custom function names (say `AddFoo` and `RemoveFoo` accordingly)
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// by tailoring ScopedObservationTraits<> for the given Source and Observer --
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// see `base/scoped_observation_traits.h` for details.
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//
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template <class Source, class Observer>
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class ScopedMultiSourceObservation {
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public:
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explicit ScopedMultiSourceObservation(Observer* observer)
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: observer_(observer) {}
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ScopedMultiSourceObservation(const ScopedMultiSourceObservation&) = delete;
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ScopedMultiSourceObservation& operator=(const ScopedMultiSourceObservation&) =
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delete;
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~ScopedMultiSourceObservation() { RemoveAllObservations(); }
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// Adds the object passed to the constructor as an observer on |source|.
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void AddObservation(Source* source) {
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CHECK(!IsObservingSource(source));
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sources_.push_back(source);
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Traits::AddObserver(source, observer_);
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}
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// Remove the object passed to the constructor as an observer from |source|.
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void RemoveObservation(Source* source) {
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auto it = base::ranges::find(sources_, source);
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CHECK(it != sources_.end());
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sources_.erase(it);
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Traits::RemoveObserver(source, observer_);
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}
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// Remove the object passed to the constructor as an observer from all sources
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// it's observing.
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void RemoveAllObservations() {
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for (Source* source : sources_) {
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Traits::RemoveObserver(source, observer_);
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}
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sources_.clear();
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}
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// Returns true if any source is being observed.
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bool IsObservingAnySource() const { return !sources_.empty(); }
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// Returns true if |source| is being observed.
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bool IsObservingSource(Source* source) const {
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DCHECK(source);
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return base::Contains(sources_, source);
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}
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// Returns the number of sources being observed.
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size_t GetSourcesCount() const { return sources_.size(); }
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// Returns the sources being observed. Note: It is invalid to add or remove
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// sources while iterating on it.
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const std::vector<raw_ptr<Source>>& sources() const { return sources_; }
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private:
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using Traits = ScopedObservationTraits<Source, Observer>;
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const raw_ptr<Observer> observer_;
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std::vector<raw_ptr<Source>> sources_;
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};
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} // namespace base
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#endif // BASE_SCOPED_MULTI_SOURCE_OBSERVATION_H_
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