How to make a layer selectable or not selectable in MapInfo MapXtreme

In this tutorial i will show you that how can we make a layer selectable  or not selectable

/ / All the layers are not optional
                 MapInfo.Mapping.LayerHelper.SetSelectable (item, false);
   / / A layer is not optional
             foreach (MapInfo.Mapping.IMapLayer layer in mapControl1.Map.Layers)
             {
                 if (object.ReferenceEquals (layer, mapControl1.Map.Layers ["GZ_River_LL"]))
                 {
                     MapInfo.Mapping.LayerHelper.SetSelectable (layer, false);
                 }
         }