Introduce a new way of using ScopedUserPrefUpdate that ensures notifications are sent.

This new ScopedUserPrefUpdate class should subsitute access to GetMutableList() and GetMutableDictionary() in PrefService. It ensures that update notifications are sent.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6757011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@79821 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 89 insertions, 2 deletions

diff --git a/chrome/browser/prefs/scoped_user_pref_update.h b/chrome/browser/prefs/scoped_user_pref_update.h
index 8992d09..69572fa 100644
--- a/chrome/browser/prefs/scoped_user_pref_update.h
+++ b/chrome/browser/prefs/scoped_user_pref_update.h
@@ -1,16 +1,63 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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
-// are changed.
+// or dictionaries are changed.
 
 #ifndef CHROME_BROWSER_PREFS_SCOPED_USER_PREF_UPDATE_H_
 #define CHROME_BROWSER_PREFS_SCOPED_USER_PREF_UPDATE_H_
 #pragma once
 
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/scoped_ptr.h"
+#include "base/threading/non_thread_safe.h"
+#include "base/values.h"
 #include "chrome/browser/prefs/pref_service.h"
 
+class DictionaryValue;
+class ListValue;
+class PrefService;
+
+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 ScopedUserPrefUpdateBase : public base::NonThreadSafe {
+ protected:
+  ScopedUserPrefUpdateBase(PrefService* service, const char* path);
+
+  // Calls Notify().
+  virtual ~ScopedUserPrefUpdateBase();
+
+  // Sets |value_| to |service_|->GetMutableUserPref and returns it.
+  Value* Get(Value::ValueType type);
+
+ private:
+  // If |value_| is not null, triggers a notification of PrefObservers and
+  // resets |value_|.
+  virtual 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).
+  Value* value_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdateBase);
+};
+
+}  // namespace subtle
+
+// TODO(battre) This class is legacy and will be substituted by
+// ScopedUserPrefUpdateTemplate soon. http://crbug.com/58489
 class ScopedUserPrefUpdate {
  public:
   ScopedUserPrefUpdate(PrefService* service, const char* path);
@@ -21,4 +68,44 @@ class ScopedUserPrefUpdate {
   std::string path_;
 };
 
+// TODO(battre) Rename ScopedUserPrefUpdateTemplate to ScopedUserPrefUpdate
+// once the legacy class above is gone. http://crbug.com/58489
+
+// 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, Value::ValueType type_enum_value>
+class ScopedUserPrefUpdateTemplate : public subtle::ScopedUserPrefUpdateBase {
+ public:
+  ScopedUserPrefUpdateTemplate(PrefService* service, const char* path)
+      : ScopedUserPrefUpdateBase(service, path) {}
+
+  // Triggers an update notification if Get() was called.
+  virtual ~ScopedUserPrefUpdateTemplate() {}
+
+  // 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 T* Get() {
+    return static_cast<T*>(
+        subtle::ScopedUserPrefUpdateBase::Get(type_enum_value));
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdateTemplate);
+};
+
+typedef ScopedUserPrefUpdateTemplate<DictionaryValue, Value::TYPE_DICTIONARY>
+    DictionaryPrefUpdate;
+typedef ScopedUserPrefUpdateTemplate<ListValue, Value::TYPE_LIST>
+    ListPrefUpdate;
+
 #endif  // CHROME_BROWSER_PREFS_SCOPED_USER_PREF_UPDATE_H_