Collection Object

Description

A Collection object is an ordered set of items that can be referred to as a unit.

Remarks

The Collection object provides a convenient way to refer to a related group of items as a single object. The items, or members, in a collection need only be related by the fact that they exist in the collection. Members of a collection don't have to share the same data type.

A collection can be created the same way other objects are created. For example:

Dim X As New Collection

Once a collection is created, members can be added using the Add method and removed using the Remove method. Specific members can be returned from the collection using the Item method, while the entire collection can be iterated using the For Each...Next statement.

Properties

Count property.

Methods

Add method, Item method, Remove method.

See Also

Add method, For Each…Next statement, Item method, Remove method.

Specifics (Microsoft Access)

In Microsoft Access, a Collection object can consist of a set of objects of any type. You can create a Collection object that consists of several objects of the same type or objects of different types.

The collection defined by a Collection object can contain any combination of Microsoft Access objects, Data Access Objects (DAO), and objects from any other application that exposes its objects to Microsoft Access. You can also add a Collection object to a collection defined by a Collection object.

The collection can also contain user-defined objects that you create in Microsoft Access. For example, you can create user-defined objects with custom methods and properties from a form module or report module. Then you can add these objects to a collection defined by a Collection object, and manipulate them as a set.

Example

This example creates a Collection object (MyClasses), and then creates a dialog box in which users can add objects to the collection. To see how this works, choose the Class Module command from the Insert menu and declare a public variable called InstanceName at module level of Class1 (type Public InstanceName) to hold the names of each instance. Leave the default name as Class1. Copy and paste the following code into the General section of another module, and then start it with the statement ClassNamer in another procedure. (This example only works with host applications that support classes.)

Sub ClassNamer()
    Dim MyClasses As New Collection    ' Create a Collection object.
    Dim Num                                ' Counter for individualizing keys.
    Dim Msg As String    ' Variable to hold prompt string.
    Dim TheName, MyObject, NameList    ' Variants to hold information.
    Do
        Dim Inst As New Class1        ' Create a new instance of Class1.
        Num = Num + 1                    ' Increment Num, then get a name.
        Msg = "Please enter a name for this object." & Chr(13) _
            & "Press Cancel to see names in collection."
        TheName = InputBox(Msg, "Name the Collection Items")
        Inst.InstanceName = TheName    ' Put name in object instance.
        ' If user entered name, add it to the collection.
        If Inst.InstanceName <> "" Then
            ' Add the named object to the collection.
            MyClasses.Add item := Inst, key := CStr(Num)
        End If
        ' Clear the current reference in preparation for next one.
        Set Inst = Nothing
    Loop Until TheName = ""
    For Each MyObject In MyClasses    ' Create list of names.
        NameList = NameList & MyObject.InstanceName & Chr(13)
    Next MyObject
    ' Display the list of names in a message box.
    MsgBox NameList, , "Instance Names In MyClasses Collection"

    For Num = 1 To MyClasses.Count    ' Remove name from the collection.
        MyClasses.Remove 1                ' Since collections are reindexed
                                            ' automatically, remove the first
    Next                                    ' member on each iteration.
End Sub