Reland: Closure-based API to PrefChangeObserver and PrefMember.

chrome/browser/api/prefs/pref_member.h

 // Copyright (c) 2012 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.
 //
 // A helper class that stays in sync with a preference (bool, int, real,
 // string or filepath).  For example:
 //
 // class MyClass {
 //  public:
 //   MyClass(PrefService* prefs) {
@@ skipping 10 matching lines @@
 // notify MyClass of changes. Note that if you use SetValue(), the observer
 // will not be notified.
 
 #ifndef CHROME_BROWSER_API_PREFS_PREF_MEMBER_H_
 #define CHROME_BROWSER_API_PREFS_PREF_MEMBER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/callback_forward.h"
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop_proxy.h"
 #include "base/prefs/public/pref_observer.h"
 #include "base/values.h"
 
 class PrefServiceBase;
 
 namespace subtle {
 
 class PrefMemberBase : public PrefObserver {
+ public:
+  // Type of callback you can register if you need to know the name of
+  // the pref that is changing.
+  typedef base::Callback<void(const std::string&)> NamedChangeCallback;
+
  protected:
   class Internal : public base::RefCountedThreadSafe<Internal> {
    public:
     Internal();
 
     // Update the value, either by calling |UpdateValueInternal| directly
     // or by dispatching to the right thread.
     // Takes ownership of |value|.
     void UpdateValue(base::Value* value,
                      bool is_managed,
@@ skipping 31 matching lines @@
     mutable bool is_user_modifiable_;
 
     DISALLOW_COPY_AND_ASSIGN(Internal);
   };
 
   PrefMemberBase();
   virtual ~PrefMemberBase();
 
   // See PrefMember<> for description.
   void Init(const char* pref_name, PrefServiceBase* prefs,
-            PrefObserver* observer);
+            const NamedChangeCallback& observer);
+  void Init(const char* pref_name, PrefServiceBase* prefs);
 
   virtual void CreateInternal() const = 0;
 
   // See PrefMember<> for description.
   void Destroy();
 
   void MoveToThread(const scoped_refptr<base::MessageLoopProxy>& message_loop);
 
   // PrefObserver
   virtual void OnPreferenceChanged(PrefServiceBase* service,
@@ skipping 12 matching lines @@
   // it hasn't been loaded yet.
   void VerifyPref() const;
 
   const std::string& pref_name() const { return pref_name_; }
   PrefServiceBase* prefs() { return prefs_; }
   const PrefServiceBase* prefs() const { return prefs_; }
 
   virtual Internal* internal() const = 0;
 
  private:
+  // Used to allow registering plain base::Closure callbacks.
+  static void InvokeUnnamedCallback(const base::Closure& callback,
+                                    const std::string& pref_name);
+
   // Ordered the members to compact the class instance.
   std::string pref_name_;
-  PrefObserver* observer_;
+  scoped_ptr<NamedChangeCallback> observer_;

[Mattias Nissler (ping if slow), 2012/11/09 14:47:50]

Other code uses base::Callback::is_null() for determining whether a callback is
actually valid instead of wrapping it in a scoped_ptr. Is this variant
preferable?

If you went with the is_null solution you could also drop the 2-parameter form
if PreferMemberBase::Init.

   PrefServiceBase* prefs_;
 
  protected:
   bool setting_value_;
 };
 
 // This function implements StringListPrefMember::UpdateValue().
 // It is exposed here for testing purposes.
 bool PrefMemberVectorStringUpdate(const Value& value,
                                   std::vector<std::string>* string_vector);
 
 }  // namespace subtle
 
 template <typename ValueType>
 class PrefMember : public subtle::PrefMemberBase {
  public:
   // Defer initialization to an Init method so it's easy to make this class be
   // a member variable.
   PrefMember() {}
   virtual ~PrefMember() {}
 
-  // Do the actual initialization of the class.  |observer| may be null if you
-  // don't want any notifications of changes.
-  // This method should only be called on the UI thread.
+  // Do the actual initialization of the class.  Use the two-parameter
+  // version if you don't want any notifications of changes.  This
+  // method should only be called on the UI thread.
+  void Init(const char* pref_name, PrefServiceBase* prefs,
+            const NamedChangeCallback& observer) {
+    subtle::PrefMemberBase::Init(pref_name, prefs, observer);
+  }
+  void Init(const char* pref_name, PrefServiceBase* prefs,
+            const base::Closure& observer) {
+    subtle::PrefMemberBase::Init(
+        pref_name, prefs,
+        base::Bind(&PrefMemberBase::InvokeUnnamedCallback, observer));
+  }
+  void Init(const char* pref_name, PrefServiceBase* prefs) {
+    subtle::PrefMemberBase::Init(pref_name, prefs);
+  }
+
+  // Deprecated version of Init.
   void Init(const char* pref_name, PrefServiceBase* prefs,
             PrefObserver* observer) {
-    subtle::PrefMemberBase::Init(pref_name, prefs, observer);
+    if (observer) {
+      Init(pref_name, prefs, base::Bind(&PrefObserver::OnPreferenceChanged,
+                                        base::Unretained(observer), prefs));
+    } else {
+      Init(pref_name, prefs);
+    }
   }
 
   // Unsubscribes the PrefMember from the PrefService. After calling this
   // function, the PrefMember may not be used any more on the UI thread.
   // Assuming |MoveToThread| was previously called, |GetValue|, |IsManaged|,
   // and |IsUserModifiable| can still be called from the other thread but
   // the results will no longer update from the PrefService.
   // This method should only be called on the UI thread.
   void Destroy() {
     subtle::PrefMemberBase::Destroy();
@@ skipping 92 matching lines @@
 
 typedef PrefMember<bool> BooleanPrefMember;
 typedef PrefMember<int> IntegerPrefMember;
 typedef PrefMember<double> DoublePrefMember;
 typedef PrefMember<std::string> StringPrefMember;
 typedef PrefMember<FilePath> FilePathPrefMember;
 // This preference member is expensive for large string arrays.
 typedef PrefMember<std::vector<std::string> > StringListPrefMember;
 
 #endif  // CHROME_BROWSER_API_PREFS_PREF_MEMBER_H_