The DataRepeater has to have its DataSource property set for AddNew to work. It's designed to be data bound.
You can set the dataSource to a list of objects. Then whenever you add to the list, the dataRepeater will automatically show the new items.
Example:
Public Class dataitem
Public Sub New(text As String)
Me.text = text
End Sub
Public Property text As String
End Class
Public Class Form1
Public Sub New()
InitializeComponent()
Dim data As New List(Of dataitem)
data.Add(New dataitem("test1"))
data.Add(New dataitem("test2"))
DataRepeater1.DataSource = data
End Sub
End Class