blob: c90f91de11722a4b3e2ff11cdf321a4e7edf27f1 [file] [log] [blame]
// Copyright 2013 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.
// A helper class that assists preferences in firing notifications when lists
// or dictionaries are changed.
#include <string>
#include "base/macros.h"
#include "base/sequence_checker.h"
#include "base/values.h"
#include "components/prefs/pref_service.h"
#include "components/prefs/prefs_export.h"
class PrefService;
namespace base {
class DictionaryValue;
class ListValue;
} // namespace base
namespace subtle {
// Base class for ScopedUserPrefUpdateTemplate that contains the parts
// that do not depend on ScopedUserPrefUpdateTemplate's template parameter.
// We need this base class mostly for making it a friend of PrefService
// and getting access to PrefService::GetMutableUserPref and
// PrefService::ReportUserPrefChanged.
class COMPONENTS_PREFS_EXPORT ScopedUserPrefUpdateBase {
ScopedUserPrefUpdateBase(PrefService* service, const std::string& path);
// Calls Notify().
// Sets |value_| to |service_|->GetMutableUserPref and returns it.
base::Value* GetValueOfType(base::Value::Type type);
// If |value_| is not null, triggers a notification of PrefObservers and
// resets |value_|.
void Notify();
// Weak pointer.
PrefService* service_;
// Path of the preference being updated.
std::string path_;
// Cache of value from user pref store (set between Get() and Notify() calls).
base::Value* value_;
} // namespace subtle
// Class to support modifications to DictionaryValues and ListValues while
// guaranteeing that PrefObservers are notified of changed values.
// This class may only be used on the UI thread as it requires access to the
// PrefService.
template <typename T, base::Value::Type type_enum_value>
class ScopedUserPrefUpdate : public subtle::ScopedUserPrefUpdateBase {
ScopedUserPrefUpdate(PrefService* service, const std::string& path)
: ScopedUserPrefUpdateBase(service, path) {}
// Triggers an update notification if Get() was called.
virtual ~ScopedUserPrefUpdate() {}
// Returns a mutable |T| instance that
// - is already in the user pref store, or
// - is (silently) created and written to the user pref store if none existed
// before.
// Calling Get() implies that an update notification is necessary at
// destruction time.
// The ownership of the return value remains with the user pref store.
// Virtual so it can be overriden in subclasses that transform the value
// before returning it (for example to return a subelement of a dictionary).
virtual T* Get() { return static_cast<T*>(GetValueOfType(type_enum_value)); }
T& operator*() { return *Get(); }
T* operator->() { return Get(); }
typedef ScopedUserPrefUpdate<base::DictionaryValue,
typedef ScopedUserPrefUpdate<base::ListValue, base::Value::Type::LIST>