Clean up pref change notification handling.

chrome/common/pref_store.h

 // Copyright (c) 2010 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 CHROME_COMMON_PREF_STORE_H_
 #define CHROME_COMMON_PREF_STORE_H_
 #pragma once
 
+#include <string>
+
+#include "base/basictypes.h"
+
 class DictionaryValue;
 class Value;
 
 // This is an abstract interface for reading and writing from/to a persistent
-// preference store, used by |PrefService|. An implementation using a JSON file
-// can be found in |JsonPrefStore|, while an implementation without any backing
-// store (currently used for testing) can be found in |DummyPrefStore|.
+// preference store, used by PrefService. An implementation using a JSON file
+// can be found in JsonPrefStore, while an implementation without any backing
+// store for testing can be found in TestingPrefStore. Furthermore, there is
+// CommandLinePrefStore, which bridges command line options to preferences and
+// ConfigurationPolicyPrefStore, which is used for hooking up configuration
+// policy with the preference subsystem.
 class PrefStore {
  public:
+  // Observer interface for monitoring PrefStore.
+  class ObserverInterface {
+   public:
+    virtual ~ObserverInterface() {}
+
+    // Called when the value for the given |key| in the store changes.
+    virtual void OnPrefValueChanged(const std::string& key) = 0;
+    // Notification about the PrefStore being fully initialized.
+    virtual void OnInitializationCompleted() = 0;
+  };
+
   // Unique integer code for each type of error so we can report them
   // distinctly in a histogram.
   // NOTE: Don't change the order here as it will change the server's meaning
   // of the histogram.
   enum PrefReadError {
     PREF_READ_ERROR_NONE = 0,
     PREF_READ_ERROR_JSON_PARSE,
     PREF_READ_ERROR_JSON_TYPE,
     PREF_READ_ERROR_ACCESS_DENIED,
     PREF_READ_ERROR_FILE_OTHER,
     PREF_READ_ERROR_FILE_LOCKED,
     PREF_READ_ERROR_NO_FILE,
     PREF_READ_ERROR_JSON_REPEAT,
     PREF_READ_ERROR_OTHER,
     PREF_READ_ERROR_FILE_NOT_SPECIFIED
   };
 
   // To require that the default value be used for a preference, a
   // PrefStore can set the value in its own prefs dictionary to the
   // sentinel Value returned by this function.
   // TODO(danno): Instead of having a sentinel value, pref stores
   // should return a richer set of information from the property
   // accessor methods to indicate that the default should be used.
   static Value* CreateUseDefaultSentinelValue();
 
   // Returns true if a value is the special sentinel value created by
   // CreateUseDefaultSentinelValue.
   static bool IsUseDefaultSentinelValue(Value* value);
 
-  virtual ~PrefStore() { }
+  PrefStore() {}
+  virtual ~PrefStore() {}
+
+  // Add and remove observers.
+  virtual void AddObserver(ObserverInterface* observer) {};

[danno, 2010/12/02 10:31:52]

= 0? If not, please check multiple inheritance guidelines.

[Mattias Nissler (ping if slow), 2010/12/02 16:38:24]

There are no cases of multiple inheritance concerning PrefStore.

+  virtual void RemoveObserver(ObserverInterface* observer) {};
+
+  // Whether the store has completed all asynchronous initialization.
+  virtual bool IsInitializationComplete() { return true; }
 
   // Whether the store is in a pseudo-read-only mode where changes are not
   // actually persisted to disk.  This happens in some cases when there are
   // read errors during startup.
   virtual bool ReadOnly() { return true; }
 
   // TODO(danno): PrefValueStore shouldn't allow direct access to the
   // DictionaryValue. Instead, it should have getters that return a
   // richer set of information for a pref, including if the store
   // wants to return the default value for a preference.
   virtual DictionaryValue* prefs() const = 0;
 
   virtual PrefReadError ReadPrefs() = 0;
 
   virtual bool WritePrefs() { return true; }
 
   virtual void ScheduleWritePrefs() { }
+
+  DISALLOW_COPY_AND_ASSIGN(PrefStore);
 };
 
 #endif  // CHROME_COMMON_PREF_STORE_H_