base/prefs/pref_registry.h

   1 // Copyright (c) 2012 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 BASE_PREFS_PREF_REGISTRY_H_
   6 #define BASE_PREFS_PREF_REGISTRY_H_
   7
   8 #include "base/containers/hash_tables.h"
   9 #include "base/memory/ref_counted.h"
  10 #include "base/prefs/base_prefs_export.h"
  11 #include "base/prefs/pref_value_map.h"
  12
  13 namespace base {
  14 class Value;
  15 }
  16
  17 class DefaultPrefStore;
  18 class PrefStore;
  19
  20 // Preferences need to be registered with a type and default value
  21 // before they are used.
  22 //
  23 // The way you use a PrefRegistry is that you register all required
  24 // preferences on it (via one of its subclasses), then pass it as a
  25 // construction parameter to PrefService.
  26 //
  27 // Currently, registrations after constructing the PrefService will
  28 // also work, but this is being deprecated.
  29 class BASE_PREFS_EXPORT PrefRegistry : public base::RefCounted<PrefRegistry> {
  30  public:
  31   // Registration flags that can be specified which impact how the pref will
  32   // behave or be stored. This will be passed in a bitmask when the pref is
  33   // registered. Subclasses of PrefRegistry can specify their own flags. Care
  34   // must be taken to ensure none of these overlap with the flags below.
  35   enum PrefRegistrationFlags : uint32 {
  36     // No flags are specified.
  37     NO_REGISTRATION_FLAGS = 0,
  38
  39     // The first 8 bits are reserved for subclasses of PrefRegistry to use.
  40
  41     // This marks the pref as "lossy". There is no strict time guarantee on when
  42     // a lossy pref will be persisted to permanent storage when it is modified.
  43     LOSSY_PREF = 1 << 8,
  44   };
  45
  46   typedef PrefValueMap::const_iterator const_iterator;
  47   typedef base::hash_map<std::string, uint32> PrefRegistrationFlagsMap;
  48
  49   PrefRegistry();
  50
  51   // Retrieve the set of registration flags for the given preference. The return
  52   // value is a bitmask of PrefRegistrationFlags.
  53   uint32 GetRegistrationFlags(const std::string& pref_name) const;
  54
  55   // Gets the registered defaults.
  56   scoped_refptr<PrefStore> defaults();
  57
  58   // Allows iteration over defaults.
  59   const_iterator begin() const;
  60   const_iterator end() const;
  61
  62   // Changes the default value for a preference. Takes ownership of |value|.
  63   //
  64   // |pref_name| must be a previously registered preference.
  65   void SetDefaultPrefValue(const std::string& pref_name, base::Value* value);
  66
  67  protected:
  68   friend class base::RefCounted<PrefRegistry>;
  69   virtual ~PrefRegistry();
  70
  71   // Used by subclasses to register a default value and registration flags for
  72   // a preference. |flags| is a bitmask of |PrefRegistrationFlags|.
  73   void RegisterPreference(const std::string& path,
  74                           base::Value* default_value,
  75                           uint32 flags);
  76
  77   scoped_refptr<DefaultPrefStore> defaults_;
  78
  79   // A map of pref name to a bitmask of PrefRegistrationFlags.
  80   PrefRegistrationFlagsMap registration_flags_;
  81
  82  private:
  83   DISALLOW_COPY_AND_ASSIGN(PrefRegistry);
  84 };
  85
  86 #endif  // BASE_PREFS_PREF_REGISTRY_H_