VB.NET Language in a Nutshell, Second Edition

Name

Collection.Item Method

Class

Microsoft.VisualBasic.Collection

Syntax

                  objectvariable.Item(index)

objectvariable (required; Collection Object)

An object variable of type Collection

index (required; Integer or String)

Either the index (the ordinal position) of the object in the collection, or the unique key name belonging to the object

Description

Returns the member of the collection for the specified key or ordinal position

Programming Tips and Gotchas

• When writing wrapper classes for collections, you can make your object model more readable by making the name of the property that wraps the Item method the same as the name of the object obtained from the collection. For example, if your collection class is called Employees and is a collection of Employee records, your object model reads much better to have an Employee Property procedure, as follows:

  Public Property Employee(vKey as Object) As Boolean
     Get
        Employee = mcolEmployees.Item(vKey)
     End Get
  . . .
  End Property

  Note that in the previous Property procedure, the parameter is passed as an object so that the argument can be either a string (the item’s key) or an integer (the item’s ordinal position).

• There is no Exists method in the Collection object, so you cannot find out in advance if a particular key exists within the collection. However, you can create an Exists function by calling the Item method with a given key and returning an appropriate value based on whether an error occurred, as the following code shows:

  Public Function ...