Server.Items.HousePlacementTool.OnDoubleClick C# (CSharp) Method

        public override void OnDoubleClick( Mobile from )
        {
            if ( IsChildOf( from.Backpack ) )
                from.SendGump( new HousePlacementCategoryGump( from ) );
            else
                from.SendLocalizedMessage( 1042001 ); // That must be in your pack for you to use it.
        }