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Side by Side Diff: components/prefs/scoped_user_pref_update.h

Issue 1645073005: Revert of Move base/prefs to components/prefs (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Created 4 years, 10 months ago
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1 // Copyright 2013 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 // A helper class that assists preferences in firing notifications when lists
6 // or dictionaries are changed.
7
8 #ifndef BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
9 #define BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
10
11 #include <string>
12
13 #include "base/macros.h"
14 #include "base/prefs/base_prefs_export.h"
15 #include "base/prefs/pref_service.h"
16 #include "base/threading/non_thread_safe.h"
17 #include "base/values.h"
18
19 class PrefService;
20
21 namespace base {
22 class DictionaryValue;
23 class ListValue;
24 }
25
26 namespace subtle {
27
28 // Base class for ScopedUserPrefUpdateTemplate that contains the parts
29 // that do not depend on ScopedUserPrefUpdateTemplate's template parameter.
30 //
31 // We need this base class mostly for making it a friend of PrefService
32 // and getting access to PrefService::GetMutableUserPref and
33 // PrefService::ReportUserPrefChanged.
34 class BASE_PREFS_EXPORT ScopedUserPrefUpdateBase : public base::NonThreadSafe {
35 protected:
36 ScopedUserPrefUpdateBase(PrefService* service, const std::string& path);
37
38 // Calls Notify().
39 ~ScopedUserPrefUpdateBase();
40
41 // Sets |value_| to |service_|->GetMutableUserPref and returns it.
42 base::Value* GetValueOfType(base::Value::Type type);
43
44 private:
45 // If |value_| is not null, triggers a notification of PrefObservers and
46 // resets |value_|.
47 void Notify();
48
49 // Weak pointer.
50 PrefService* service_;
51 // Path of the preference being updated.
52 std::string path_;
53 // Cache of value from user pref store (set between Get() and Notify() calls).
54 base::Value* value_;
55
56 DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdateBase);
57 };
58
59 } // namespace subtle
60
61 // Class to support modifications to DictionaryValues and ListValues while
62 // guaranteeing that PrefObservers are notified of changed values.
63 //
64 // This class may only be used on the UI thread as it requires access to the
65 // PrefService.
66 template <typename T, base::Value::Type type_enum_value>
67 class ScopedUserPrefUpdate : public subtle::ScopedUserPrefUpdateBase {
68 public:
69 ScopedUserPrefUpdate(PrefService* service, const std::string& path)
70 : ScopedUserPrefUpdateBase(service, path) {}
71
72 // Triggers an update notification if Get() was called.
73 virtual ~ScopedUserPrefUpdate() {}
74
75 // Returns a mutable |T| instance that
76 // - is already in the user pref store, or
77 // - is (silently) created and written to the user pref store if none existed
78 // before.
79 //
80 // Calling Get() implies that an update notification is necessary at
81 // destruction time.
82 //
83 // The ownership of the return value remains with the user pref store.
84 // Virtual so it can be overriden in subclasses that transform the value
85 // before returning it (for example to return a subelement of a dictionary).
86 virtual T* Get() {
87 return static_cast<T*>(GetValueOfType(type_enum_value));
88 }
89
90 T& operator*() {
91 return *Get();
92 }
93
94 T* operator->() {
95 return Get();
96 }
97
98 private:
99 DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdate);
100 };
101
102 typedef ScopedUserPrefUpdate<base::DictionaryValue,
103 base::Value::TYPE_DICTIONARY>
104 DictionaryPrefUpdate;
105 typedef ScopedUserPrefUpdate<base::ListValue, base::Value::TYPE_LIST>
106 ListPrefUpdate;
107
108 #endif // BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
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