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// 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.
#ifndef BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
#define BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
#include <string>
#include "base/basictypes.h"
#include "base/prefs/base_prefs_export.h"
#include "base/prefs/pref_service.h"
#include "base/threading/non_thread_safe.h"
#include "base/values.h"
class PrefService;
namespace base {
class DictionaryValue;
class ListValue;
}
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 BASE_PREFS_EXPORT ScopedUserPrefUpdateBase : public base::NonThreadSafe {
protected:
ScopedUserPrefUpdateBase(PrefService* service, const char* path);
// Calls Notify().
~ScopedUserPrefUpdateBase();
// Sets |value_| to |service_|->GetMutableUserPref and returns it.
base::Value* GetValueOfType(base::Value::Type type);
private:
// 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_;
DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdateBase);
};
} // 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 {
public:
ScopedUserPrefUpdate(PrefService* service, const char* 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();
}
private:
DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdate);
};
typedef ScopedUserPrefUpdate<base::DictionaryValue,
base::Value::TYPE_DICTIONARY>
DictionaryPrefUpdate;
typedef ScopedUserPrefUpdate<base::ListValue, base::Value::TYPE_LIST>
ListPrefUpdate;
#endif // BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
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