ctkIconEnginePlugin::keys returns ctkIconEngine

When saving a QIcon into a QDataStream, the icon engine key is used.
Later, when loading a QIcon from a QDataStream, that same key is used to
find the icon engine used.
ctkPixmapIconEngine was the key saved but couldn't be retrieved because
the plugin wasn't exposing it.
You might have to clear your Trolltech registry (Qt Factory Cache*) in
order for the ctkIconEnginePlugin meta information to be reloaded

Libs/Widgets/ctkIconEnginePlugin.cpp

@@ -59,6 +59,9 @@ QIconEngineV2* ctkIconEnginePlugin::create(const QString& fileName)
 QStringList ctkIconEnginePlugin::keys()const
 {
   QStringList supportedKeys;
+  // While ctkIconEngine supports all the image formats, it is uniquely defined
+  // with "ctkIconEngine".
+  supportedKeys << "ctkIconEngine";
   foreach(QByteArray byteArray, QImageReader::supportedImageFormats())
     {
     supportedKeys << QString(byteArray);
@@ -154,3 +157,9 @@ QStringList ctkIconEngine::sizeDirectories()const
   Q_D(const ctkIconEngine);
   return d->SizeDirectories;
 }
+
+//------------------------------------------------------------------------------
+QString ctkIconEngine::key() const
+{
+  return QLatin1String("ctkIconEngine");
+}

Libs/Widgets/ctkIconEnginePlugin.h

@@ -107,6 +107,8 @@ public:
   /// "LowDef", "HighDef"
   void setSizeDirectories(const QStringList& sizeDirectories);
   QStringList sizeDirectories()const;
+
+  virtual QString key()const;
  
 protected:
   QScopedPointer<ctkIconEnginePrivate> d_ptr;