'宣言
 
Protected Overridable Function RenderItem
    (Of T2 As ComboEditorItemBase(Of TControl2),
     TControl2 As FrameworkElement)( _
   ByVal comboEditorItem As T2, _
   ByVal availableSize As Size _
) As Size
            protected virtual Size RenderItem<T2,TControl2>( T2 comboEditorItem, Size availableSize ) where T2: ComboEditorItemBase<TControl2> where TControl2: FrameworkElement