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// Copyright 2017 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.
#include "base/callback.h"
#include "base/macros.h"
#include "base/observer_list.h"
#include "components/keyed_service/core/keyed_service.h"
#include "components/prefs/pref_observer.h"
class PrefService;
// There are more than 1000 font prefs and several subsystems need to be
// notified when a font changes. Registering for 1000 font change notifications
// is inefficient and slows down other pref notifications, and having each font
// subsystem registering "any preference changed" observers is also
// inefficient.
// This class registers for "any preference changed" notifications, filters
// for font pref changes only, and then issues notifications to registered
// observers.
// There is one FontPrefChangeNotifier per Profile. Construct one with the
// FontPrefChangeNotifierFactory.
class FontPrefChangeNotifier : public PrefObserver, public KeyedService {
// The parameter is the full name of the font pref that changed.
using Callback = base::RepeatingCallback<void(const std::string&)>;
// Instantiate this subclass to scope an observer notification. The registrar
// can have only one callback.
class Registrar {
bool is_registered() const { return !!notifier_; }
// Start watching for changes.
void Register(FontPrefChangeNotifier* notifier,
FontPrefChangeNotifier::Callback cb);
// Optional way to unregister before the Registrar object goes out of
// scope. The object must currently be registered.
void Unregister();
friend FontPrefChangeNotifier;
FontPrefChangeNotifier* notifier_ = nullptr;
FontPrefChangeNotifier::Callback callback_;
// The pref service must outlive this class.
explicit FontPrefChangeNotifier(PrefService* pref_service);
~FontPrefChangeNotifier() override;
friend Registrar;
void AddRegistrar(Registrar* registrar);
void RemoveRegistrar(Registrar* registrar);
// PrefObserver implementation.
void OnPreferenceChanged(PrefService* service,
const std::string& pref_name) override;
PrefService* pref_service_; // Non-owning.
// Non-owning pointers to the Registrars that have registered themselves
// with us. We expect few registrars.
base::ObserverList<Registrar>::Unchecked registrars_;