Pref service: Add a ScopedDictionaryPrefUpdate to track value changes.

services/preferences/public/cpp/scoped_pref_update.h

+// Copyright 2017 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 SERVICES_PREFERENCES_PUBLIC_CPP_SCOPED_PREF_UPDATE_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_SCOPED_PREF_UPDATE_H_
+
+#include <memory>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "base/strings/string16.h"
+#include "base/strings/string_piece.h"
+#include "base/values.h"
+
+class PrefService;
+
+namespace prefs {
+class DictionaryValueUpdate;
+
+// An update to a dictionary value pref.

[tibell, 2017/04/12 07:13:52]

Could you include an example code snippet of how to use this class?

+class ScopedDictionaryPrefUpdate {
+ public:
+  ScopedDictionaryPrefUpdate(PrefService* service, base::StringPiece path);
+
+  // Notifies if necessary.
+  virtual ~ScopedDictionaryPrefUpdate();
+
+  virtual DictionaryValueUpdate* Get();
+
+  DictionaryValueUpdate* operator->();
+
+ private:
+  friend class DictionaryValueUpdate;
+  // If |value_| is not null, triggers a notification of PrefObservers and
+  // resets |value_|.
+  void Notify();
+
+  void RecordPath(const std::vector<std::string>& path);
+  DictionaryValueUpdate* Insert(
+      std::unique_ptr<DictionaryValueUpdate> dictionary_value_update);
+
+  // 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).
+  DictionaryValueUpdate* value_;

[tibell, 2017/04/12 07:13:52]

Owned?

+
+  std::set<std::vector<std::string>> updated_paths_;
+
+  std::vector<std::unique_ptr<DictionaryValueUpdate>> updates_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedDictionaryPrefUpdate);
+};
+
+// A wrapper around base::DictionaryValue that reports changes to its contents
+// to a ScopedDictionaryPrefUpdate.
+class DictionaryValueUpdate {
+ public:
+  ~DictionaryValueUpdate();
+  bool HasKey(base::StringPiece key) const;
+
+  // Returns the number of Values in this dictionary.
+  size_t size() const;
+
+  // Returns whether the dictionary is empty.
+  bool empty() const;
+
+  // Clears any current contents of this dictionary.
+  void Clear();
+
+  // Sets the Value associated with the given path starting from this object.
+  // A path has the form "<key>" or "<key>.<key>.[...]", where "." indexes
+  // into the next DictionaryValue down.  Obviously, "." can't be used
+  // within a key, but there are no other restrictions on keys.
+  // If the key at any step of the way doesn't exist, or exists but isn't
+  // a DictionaryValue, a new DictionaryValue will be created and attached
+  // to the path in that location. |in_value| must be non-null.
+  void Set(base::StringPiece path, std::unique_ptr<base::Value> in_value);
+
+  // Convenience forms of Set().  These methods will replace any existing
+  // value at that path, even if it has a different type.
+  void SetBoolean(base::StringPiece path, bool in_value);
+  void SetInteger(base::StringPiece path, int in_value);
+  void SetDouble(base::StringPiece path, double in_value);
+  void SetString(base::StringPiece path, base::StringPiece in_value);
+  void SetString(base::StringPiece path, const base::string16& in_value);
+  DictionaryValueUpdate* SetDictionary(
+      base::StringPiece path,
+      std::unique_ptr<base::DictionaryValue> in_value);
+
+  // Like Set(), but without special treatment of '.'.  This allows e.g. URLs to
+  // be used as paths.
+  void SetWithoutPathExpansion(base::StringPiece key,
+                               std::unique_ptr<base::Value> in_value);
+
+  // Convenience forms of SetWithoutPathExpansion().
+  void SetBooleanWithoutPathExpansion(base::StringPiece path, bool in_value);
+  void SetIntegerWithoutPathExpansion(base::StringPiece path, int in_value);
+  void SetDoubleWithoutPathExpansion(base::StringPiece path, double in_value);
+  void SetStringWithoutPathExpansion(base::StringPiece path,
+                                     base::StringPiece in_value);
+  void SetStringWithoutPathExpansion(base::StringPiece path,
+                                     const base::string16& in_value);
+  DictionaryValueUpdate* SetDictionaryWithoutPathExpansion(
+      base::StringPiece path,
+      std::unique_ptr<base::DictionaryValue> in_value);
+
+  // These are convenience forms of Get().  The value will be retrieved
+  // and the return value will be true if the path is valid and the value at
+  // the end of the path can be returned in the form specified.
+  // |out_value| is optional and will only be set if non-NULL.
+  bool GetBoolean(base::StringPiece path, bool* out_value) const;
+  bool GetInteger(base::StringPiece path, int* out_value) const;
+  // Values of both type Type::INTEGER and Type::DOUBLE can be obtained as
+  // doubles.
+  bool GetDouble(base::StringPiece path, double* out_value) const;
+  bool GetString(base::StringPiece path, std::string* out_value) const;
+  bool GetString(base::StringPiece path, base::string16* out_value) const;
+  bool GetBinary(base::StringPiece path, const base::Value** out_value) const;
+  bool GetDictionary(base::StringPiece path,
+                     const base::DictionaryValue** out_value) const;
+  bool GetDictionary(base::StringPiece path, DictionaryValueUpdate** out_value);
+  bool GetList(base::StringPiece path, const base::ListValue** out_value) const;
+  bool GetList(base::StringPiece path, base::ListValue** out_value);
+
+  // Like Get(), but without special treatment of '.'.  This allows e.g. URLs to
+  // be used as paths.
+  bool GetBooleanWithoutPathExpansion(base::StringPiece key,
+                                      bool* out_value) const;
+  bool GetIntegerWithoutPathExpansion(base::StringPiece key,
+                                      int* out_value) const;
+  bool GetDoubleWithoutPathExpansion(base::StringPiece key,
+                                     double* out_value) const;
+  bool GetStringWithoutPathExpansion(base::StringPiece key,
+                                     std::string* out_value) const;
+  bool GetStringWithoutPathExpansion(base::StringPiece key,
+                                     base::string16* out_value) const;
+  bool GetDictionaryWithoutPathExpansion(
+      base::StringPiece key,
+      const base::DictionaryValue** out_value) const;
+  bool GetDictionaryWithoutPathExpansion(base::StringPiece key,
+                                         DictionaryValueUpdate** out_value);
+  bool GetListWithoutPathExpansion(base::StringPiece key,
+                                   const base::ListValue** out_value) const;
+  bool GetListWithoutPathExpansion(base::StringPiece key,
+                                   base::ListValue** out_value);
+
+  // Removes the Value with the specified path from this dictionary (or one
+  // of its child dictionaries, if the path is more than just a local key).
+  // If |out_value| is non-NULL, the removed Value will be passed out via
+  // |out_value|.  If |out_value| is NULL, the removed value will be deleted.
+  // This method returns true if |path| is a valid path; otherwise it will
+  // return false and the DictionaryValue object will be unchanged.
+  bool Remove(base::StringPiece path, std::unique_ptr<base::Value>* out_value);
+
+  // Like Remove(), but without special treatment of '.'.  This allows e.g. URLs
+  // to be used as paths.
+  bool RemoveWithoutPathExpansion(base::StringPiece key,
+                                  std::unique_ptr<base::Value>* out_value);
+
+  // Removes a path, clearing out all dictionaries on |path| that remain empty
+  // after removing the value at |path|.
+  bool RemovePath(base::StringPiece path,
+                  std::unique_ptr<base::Value>* out_value);
+
+  base::DictionaryValue* AsDictionary();
+  const base::DictionaryValue* AsConstDictionary() const;
+
+ private:
+  friend class ScopedDictionaryPrefUpdate;
+
+  DictionaryValueUpdate(ScopedDictionaryPrefUpdate* update,
+                        base::DictionaryValue* value,
+                        std::vector<std::string> path);
+
+  void RecordPath(base::StringPiece path);
+  void RecordSplitPath(const std::vector<base::StringPiece>& path);
+  void RecordKey(base::StringPiece key);
+
+  std::vector<base::StringPiece> SplitPath(base::StringPiece path);
+  std::vector<std::string> ConcatPath(const std::vector<std::string>& base_path,
+                                      base::StringPiece path);
+  std::vector<std::string> ConcatPath(
+      const std::vector<std::string>& base_path,
+      const std::vector<base::StringPiece>& path);
+
+  ScopedDictionaryPrefUpdate* update_;
+  base::DictionaryValue* value_;
+  const std::vector<std::string> path_;
+};
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_SCOPED_PREF_UPDATE_H_