1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef CHROME_COMMON_PREF_STORE_H_
6#define CHROME_COMMON_PREF_STORE_H_
7#pragma once
8
9#include <string>
10
11#include "base/basictypes.h"
12#include "base/memory/ref_counted.h"
13
14class Value;
15
16// This is an abstract interface for reading and writing from/to a persistent
17// preference store, used by PrefService. An implementation using a JSON file
18// can be found in JsonPrefStore, while an implementation without any backing
19// store for testing can be found in TestingPrefStore. Furthermore, there is
20// CommandLinePrefStore, which bridges command line options to preferences and
21// ConfigurationPolicyPrefStore, which is used for hooking up configuration
22// policy with the preference subsystem.
23class PrefStore : public base::RefCounted<PrefStore> {
24 public:
25  // Observer interface for monitoring PrefStore.
26  class Observer {
27   public:
28    virtual ~Observer() {}
29
30    // Called when the value for the given |key| in the store changes.
31    virtual void OnPrefValueChanged(const std::string& key) = 0;
32    // Notification about the PrefStore being fully initialized.
33    virtual void OnInitializationCompleted() = 0;
34  };
35
36  // Return values for GetValue().
37  enum ReadResult {
38    // Value found and returned.
39    READ_OK,
40    // No value present, but skip other pref stores and use default.
41    READ_USE_DEFAULT,
42    // No value present.
43    READ_NO_VALUE,
44  };
45
46  PrefStore() {}
47
48  // Add and remove observers.
49  virtual void AddObserver(Observer* observer) {}
50  virtual void RemoveObserver(Observer* observer) {}
51
52  // Whether the store has completed all asynchronous initialization.
53  virtual bool IsInitializationComplete() const;
54
55  // Get the value for a given preference |key| and stores it in |result|.
56  // |result| is only modified if the return value is READ_OK. Ownership of the
57  // |result| value remains with the PrefStore.
58  virtual ReadResult GetValue(const std::string& key,
59                              const Value** result) const = 0;
60
61 protected:
62  friend class base::RefCounted<PrefStore>;
63  virtual ~PrefStore() {}
64
65 private:
66  DISALLOW_COPY_AND_ASSIGN(PrefStore);
67};
68
69#endif  // CHROME_COMMON_PREF_STORE_H_
70