Collection.Add(Object, String, Object, Object) Method

Definition

Namespace:

Microsoft.VisualBasic

Assembly:

Microsoft.VisualBasic.Core.dll

Source:

Collection.vb

Adds an element to a Collection object.

public void Add (object? Item, string? Key = default, object? Before = default, object? After = default);

member this.Add : obj * string * obj * obj -> unit

Public Sub Add (Item As Object, Optional Key As String = Nothing, Optional Before As Object = Nothing, Optional After As Object = Nothing)

Parameters

Item

Object

Required. An object of any type that specifies the element to add to the collection.

Key

String

Optional. A unique String expression that specifies a key string that can be used instead of a positional index to access this new element in the collection.

Before

Object

Optional. An expression that specifies a relative position in the collection. The element to be added is placed in the collection before the element identified by the Before argument. If Before is a numeric expression, it must be a number from 1 through the value of the collection's Count property. If Before is a String expression, it must correspond to the key string specified when the element being referred to was added to the collection. You cannot specify both Before and After.

After

Object

Optional. An expression that specifies a relative position in the collection. The element to be added is placed in the collection after the element identified by the After argument. If After is a numeric expression, it must be a number from 1 through the value of the collection's Count property. If After is a String expression, it must correspond to the key string specified when the element referred to was added to the collection. You cannot specify both Before and After.

Examples

The following example uses the Add method to add child objects - instances of a class called child containing a Public property name - to a collection called family. To see how this works, create a Form with two Button controls and set their Text properties to Add and List. Add the child class definition and the family declaration to the form code. Modify the _Click event handlers for the Add and List buttons as shown. The Add button allows you to add children. The List button displays the names of all the children.

Public Class child
    Public name As String
    Sub New(ByVal newName As String)
        name = newName
    End Sub
End Class
' Create a Collection object.
Private family As New Collection()
Private Sub addChild_Click() Handles Button1.Click
    Dim newName As String
    newName = InputBox("Name of new family member: ")
    If newName <> "" Then
        family.Add(New child(newName), newName)
    End If
End Sub
Private Sub listChild_Click() Handles Button2.Click
    For Each aChild As child In family
        MsgBox(aChild.name)
    Next
End Sub

Remarks

The Before or After argument must refer to an existing element of the collection; otherwise, an error occurs.

If both the Before and After arguments are omitted, the new object is added to the end of the collection.

An error also occurs if a specified Key value matches the key for an existing element of the collection.