add whether_to_draw to determine draw widget background

include/nana/gui/widgets/detail/inline_widget.hpp

@@ -70,8 +70,11 @@ namespace nana
 			/// A message to resize the inline widget
 			virtual void resize(const size&) = 0;
 
-			/// A message to set the value from a item
+			/// A message to set the value from the item
 			virtual void set(const value_type&) = 0;
+
+			/// Determines whether to draw the background of the widget
+			virtual bool whether_to_draw() const = 0;
 		};	//end class inline_widget_notifier_interface
 	}
 }

include/nana/pat/abstract_factory.hpp

@@ -19,8 +19,19 @@ namespace nana
 {
 	namespace pat
 	{
+		namespace detail
+		{
+			//A Base class for abstract factory, avoids decorated name length exceeding for a class template.
+			class abstract_factory_base
+			{
+			public:
+				virtual ~abstract_factory_base() = default;
+			};
+		}
+
 		template<typename Interface>
 		class abstract_factory
+			: public detail::abstract_factory_base
 		{
 		public:
 			using interface_type = Interface;