Magnifier: Prevent useless operation in enabling/disabling magnifier.

chrome/browser/chromeos/accessibility/magnification_manager.cc

 // 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.
 
 #include "chrome/browser/chromeos/accessibility/magnification_manager.h"
 
 #include "ash/magnifier/magnification_controller.h"
 #include "ash/magnifier/partial_magnification_controller.h"
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray_notifier.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "chrome/browser/chromeos/login/user_manager.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "chrome/common/pref_names.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
 
 namespace chromeos {
 
+namespace {
+static MagnificationManager* g_magnification_manager = NULL;
+}
+
 class MagnificationManagerImpl : public MagnificationManager,
                                  public content::NotificationObserver {
  public:
-  MagnificationManagerImpl() {
-    DCHECK(!instance_);
-    instance_ = this;
-
+  MagnificationManagerImpl() : profile_(NULL),
+                               type_(ash::MAGNIFIER_OFF) {
     registrar_.Add(this,
                   chrome::NOTIFICATION_SESSION_STARTED,
                   content::NotificationService::AllSources());
     registrar_.Add(this,
-                  chrome::NOTIFICATION_PROFILE_CREATED,
+                  chrome::NOTIFICATION_PROFILE_DESTROYED,
                   content::NotificationService::AllSources());
     registrar_.Add(this,
                   chrome::NOTIFICATION_LOGIN_WEBUI_VISIBLE,
                   content::NotificationService::AllSources());
+  }
 
-    Profile* profile = ProfileManager::GetDefaultProfileOrOffTheRecord();
-    SetProfile(profile);
-  }
-  virtual ~MagnificationManagerImpl() {}
-
-  static MagnificationManagerImpl* GetInstance() {
-    return instance_;
+  virtual ~MagnificationManagerImpl() {
+    CHECK(this == g_magnification_manager);
   }
 
   // MagnificationManager implimentation:
   ash::MagnifierType GetMagnifierType() OVERRIDE {
-    if (!profile_)
-      return ash::MAGNIFIER_OFF;
-
-    PrefService* prefs = profile_->GetPrefs();
-    if (!prefs)
-      return ash::MAGNIFIER_OFF;
-
-    return accessibility::MagnifierTypeFromName(
-        prefs->GetString(prefs::kMagnifierType).c_str());
+    return type_;
   }
 
   void SetMagnifier(ash::MagnifierType type) OVERRIDE {
+    if (type == type_)
+      return;
+
+    type_ = type;
+
     PrefService* prefs = profile_->GetPrefs();
     if (prefs) {
       std::string typeString = accessibility::ScreenMagnifierNameFromType(type);
       if (typeString != prefs->GetString(prefs::kMagnifierType)) {
         prefs->SetString(prefs::kMagnifierType, typeString);
         prefs->CommitPendingWrite();
       }
     }
 
-    ash::Shell::GetInstance()->system_tray_notifier()->
-        NotifyAccessibilityModeChanged();
-
     ash::Shell::GetInstance()->magnification_controller()->SetEnabled(
         type == ash::MAGNIFIER_FULL);
     ash::Shell::GetInstance()->partial_magnification_controller()->SetEnabled(
         type == ash::MAGNIFIER_PARTIAL);
+
+    NotifyMagnifierTypeChanged(type);
+  }
+
+  void AddObserver(MagnificationObserver* observer) OVERRIDE {
+    observers_.AddObserver(observer);
+  }
+
+  void RemoveObserver(MagnificationObserver* observer) OVERRIDE {
+    observers_.RemoveObserver(observer);
   }
 
  private:
+  void NotifyMagnifierTypeChanged(ash::MagnifierType new_type) {
+    FOR_EACH_OBSERVER(MagnificationObserver, observers_,
+                      OnMagnifierTypeChanged(new_type));
+  }
+
+  ash::MagnifierType GetMagnifierTypeFromPref() {
+    if (!profile_)
+      return ash::MAGNIFIER_OFF;
+
+    PrefService* prefs = profile_->GetPrefs();
+    if (!prefs)
+      return ash::MAGNIFIER_OFF;
+
+    return accessibility::MagnifierTypeFromName(
+        prefs->GetString(prefs::kMagnifierType).c_str());
+  }
+
   void SetProfile(Profile* profile) {
     if (pref_change_registrar_) {
       pref_change_registrar_.reset();
     }
 
     if (profile) {
       pref_change_registrar_.reset(new PrefChangeRegistrar);
       pref_change_registrar_->Init(profile->GetPrefs());
       pref_change_registrar_->Add(
           prefs::kMagnifierType,
           base::Bind(&MagnificationManagerImpl::UpdateMagnifierStatus,
                      base::Unretained(this)));
     }
 
     profile_ = profile;
     UpdateMagnifierStatus();
   }
 
   void UpdateMagnifierStatus() {
     UserManager* manager = UserManager::Get();
     if (!profile_) {
       SetMagnifier(ash::MAGNIFIER_OFF);
     } else if (manager && !manager->IsSessionStarted()) {
       SetMagnifier(ash::MAGNIFIER_FULL);
     } else {
-      ash::MagnifierType type = GetMagnifierType();
+      ash::MagnifierType type = GetMagnifierTypeFromPref();
       SetMagnifier(type);
     }
   }
 
+  // content::NotificationObserver implimentation:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE {
     switch (type) {
       case chrome::NOTIFICATION_LOGIN_WEBUI_VISIBLE:
       case chrome::NOTIFICATION_SESSION_STARTED: {
         Profile* profile = ProfileManager::GetDefaultProfileOrOffTheRecord();
         SetProfile(profile);
         break;
       }
+      case chrome::NOTIFICATION_PROFILE_DESTROYED: {
+        SetProfile(NULL);
+        break;
+      }
     }
   }
 
-  static MagnificationManagerImpl* instance_;
-
   Profile* profile_;
+  ash::MagnifierType type_;
   content::NotificationRegistrar registrar_;
   scoped_ptr<PrefChangeRegistrar> pref_change_registrar_;
 
-  friend struct DefaultSingletonTraits<MagnificationManagerImpl>;
+  ObserverList<MagnificationObserver> observers_;
   DISALLOW_COPY_AND_ASSIGN(MagnificationManagerImpl);
 };
 
-MagnificationManagerImpl* MagnificationManagerImpl::instance_ = NULL;
-
-MagnificationManager* MagnificationManager::GetInstance() {
-  return MagnificationManagerImpl::GetInstance();
+// static
+void MagnificationManager::Initialize() {
+  CHECK(g_magnification_manager == NULL);
+  g_magnification_manager = new MagnificationManagerImpl();
 }
 
-MagnificationManager* MagnificationManager::CreateInstance() {
-  // Makes sure that this is not called more than once.
-  CHECK(!GetInstance());
+// static
+void MagnificationManager::Shutdown() {
+  CHECK(g_magnification_manager);
+  delete g_magnification_manager;
+  g_magnification_manager = NULL;
+}
 
-  return new MagnificationManagerImpl();
+// static
+MagnificationManager* MagnificationManager::Get() {
+  return g_magnification_manager;
 }
 
 }  // namespace chromeos