| // 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_OBSERVATION_H_ |
| #define BASE_SCOPED_OBSERVATION_H_ |
| |
| #include <stddef.h> |
| |
| #include "base/check_op.h" |
| |
| namespace base { |
| |
| // ScopedObservation is used to keep track of singular observation, e.g. |
| // where an observer observes a single source only. |
| // |
| // Use base::ScopedMultiSourceObservation for objects that observe multiple |
| // sources. |
| // |
| // When ScopedObservation is destroyed, it removes the registered observation, |
| // if any. Basic example (as a member variable): |
| // |
| // class MyFooObserver : public FooObserver { |
| // ... |
| // private: |
| // ScopedObservation<Foo, FooObserver> foo_observation_{this}; |
| // }; |
| // |
| // MyFooObserver::MyFooObserver(Foo* foo) { |
| // foo_observation_.Observe(foo); |
| // } |
| // |
| // For cases with methods not named AddObserver/RemoveObserver: |
| // |
| // class MyFooStateObserver : public FooStateObserver { |
| // ... |
| // private: |
| // ScopedObservation<Foo, |
| // FooStateObserver, |
| // &Foo::AddStateObserver, |
| // &Foo::RemoveStateObserver> |
| // foo_observation_{this}; |
| // }; |
| template <class Source, |
| class Observer, |
| void (Source::*AddObsFn)(Observer*) = &Source::AddObserver, |
| void (Source::*RemoveObsFn)(Observer*) = &Source::RemoveObserver> |
| class ScopedObservation { |
| public: |
| explicit ScopedObservation(Observer* observer) : observer_(observer) {} |
| ScopedObservation(const ScopedObservation&) = delete; |
| ScopedObservation& operator=(const ScopedObservation&) = delete; |
| ~ScopedObservation() { Reset(); } |
| |
| // Adds the object passed to the constructor as an observer on |source|. |
| // IsObserving() must be false. |
| void Observe(Source* source) { |
| // TODO(https://crbug.com/1145565): Make this a DCHECK once ScopedObserver |
| // has been fully retired. |
| CHECK_EQ(source_, nullptr); |
| source_ = source; |
| (source_->*AddObsFn)(observer_); |
| } |
| |
| // Remove the object passed to the constructor as an observer from |source_| |
| // if currently observing. Does nothing otherwise. |
| void Reset() { |
| if (source_) { |
| (source_->*RemoveObsFn)(observer_); |
| source_ = nullptr; |
| } |
| } |
| |
| // Returns true if any source is being observed. |
| bool IsObserving() const { return source_ != nullptr; } |
| |
| // Returns true if |source| is being observed. |
| bool IsObservingSource(Source* source) const { |
| DCHECK(source); |
| return source_ == source; |
| } |
| |
| private: |
| Observer* const observer_; |
| |
| // The observed source, if any. |
| Source* source_ = nullptr; |
| }; |
| |
| } // namespace base |
| |
| #endif // BASE_SCOPED_OBSERVATION_H_ |