The Description and Rooms data members have assign access； which is important as this technique only works with properties that are not read…only。 To assign a data member or prop erty； after the object instantiation； add the With keyword； and then within curly brackets； assign each individual data member using a key/value pair； in this form： With ｛ 。Key1 = value1； 。Key2 = value2 ｝ The key represents the data member property to assign； and the value is the data that is assigned to the data member or property。 In the form example； the properties Key1 and Key2 are set。 Another technique of interest in the code to add a room grouping is the definition of a data handle when passing information： Return grouping In the implementation of AddRoomGrouping（）； the variable grouping is assigned an instance of RoomGrouping。 The declaration of the RoomGrouping class limits its scope to the LibLightingSystem assembly only； while the declaration of LightingController is public。 If the method AddRoomGrouping（） had attempted to return an instance of RoomGrouping； the piler would have marked this as an error； because the scope is inconsistent。 Assuming for the moment that you did want to return an instance of RoomGrouping； your only solution would be to declare RoomGrouping as public。 The declaration change is the wrong solution； because RoomGrouping is a class without declared methods （other than the base class methods） and has public data members。 It is a class for a specific purpose and should not be shared。 Declaring RoomGrouping as public is the wrong approach； so another solution is needed。 You could add a counter data member to the RoomGrouping declaration and return an Integer value indicating the RoomGrouping instance you are referring to in the list。 However； that would mean having access to the list somewhere； and then needing to iterate to find the appropriate RoomGrouping instance。 The solution is to declare the method as returning a type Object。 When you use Object； you are defining that your method is giving you an object instance。 The caller may or may not know what the instance type is； and in the case of AddRoomGrouping（）； it doesn’t。 But that is fine； because you； as the user； will consider the instance as a key that is managed by the class LightingController。 In technical jargon； the object instance is a handle that you hold and pass to some other ponent that knows what to do with it。 In the example； it means giving the handle to LightingController because it knows that the handle is an instance of RoomGrouping。 …………………………………………………………Page 237…………………………………………………………… C H AP TE R 8 ■ L E AR N IN G AB O U T CO M P O N E N T O R IE N TE D A R CH I TE C TU R E 215 ■Note Handles were very popular in the C programming days and were consider pointers to memory。 The caller did not know what the pointer pointed to； but kept using it when interacting with an API。 These days； handles have lost significance as we have objects； generics； and other programming constructs。 However； at times； handles are very useful。 They can help you to avoid the problem of having to expose the internal state of your API； while not having to maintain an object hierarchy to watch which objects are being referenced。 Finding a Room Grouping When a number of room groupings have been added； you will want to find a room grouping with a particular description。 As room groupings are a doubly linked list； it means needing to iterate the list； as follows （added to LightingController）： Public Function FindRoomGrouping（ByVal description As String） As Object Dim curr As RoomGrouping = _roomGroupings。NextItem Do While curr IsNot Nothing If curr。Description。pareTo（description） = 0 Then Return curr End If curr = TryCast（curr。NextItem； RoomGrouping） Loop Return Nothing End Function In the iteration code； the iteration is similar to the code illustrated earlier in the “Storing a Collection Using a Linked List” section。 The one difference is that the curr variable is of type RoomGrouping； and because NextItem is of type BaseLinkedListItem； a type cast is necessary。 Then an iteration using a While loop is carried out； during each iteration； a test paring curr。Description to the parameter description is made。 If an object is found； the handle to the RoomGrouping is returned； and if nothing is found； Nothing is returned； indicating that the RoomGrouping could not be found。 This method would be used as follows： Dim foundHandle As Object = controller。FindRoomGrouping（〃description〃） Visual Basic has constructs that make it possible to convert the LightingController class into a class that has array functionality。 The following method in LightingController declares array…like functionality； which is called a default property Default Public ReadOnly Property Item（ByVal description As String） As Object Get Return FindRoomGrouping（description） End Get End Property A Visual Basic default property is defined like a property； except that the property is prefixed with a Default keyword。 The default property is named Item by convention； and this name is used by all collection classes for consistency。 The implementation of a property is just like …………………………………………………………Page 238…………………………………………………………… 216 CH AP T E R 8 ■ L E A R N