public static void EnumerateAsync<T>(
    this IQueryable<T> query,
    XPQueryExtensions.AsyncEnumerateCallback callback
)

<ExtensionAttribute>
Public Shared Sub EnumerateAsync(Of T)(
    query As IQueryable(Of T),
    callback As XPQueryExtensions.AsyncEnumerateCallback
)

using System.Linq;
using DevExpress.Xpo;
using System.Collections;

// ...

var data = from c in session1.Query<Person>()
           where c.LastName.StartsWith("A")
           select c;

// Asynchronously loads XPQuery and enumerates it
data.EnumerateAsync(delegate(IEnumerable objects, Exception ex)
{
    // Process loaded objects here
});

'NOTE: This code snippet uses implicit typing. 
'You will need to set 'Option Infer On' in the VB file or set 'Option Infer' at the project level:

Imports System.Linq
Imports DevExpress.Xpo
Imports System.Collections

' ...

Private data = from c in session1.Query(Of Person)() where c.LastName.StartsWith("A") select c

' Asynchronously loads XPQuery and enumerates it
data.EnumerateAsync(Function(objects, ex) AnonymousMethod1(objects, ex))

Private Function AnonymousMethod1(ByVal objects As IEnumerable, 
_ByVal ex As Exception) As Boolean
    ' Process loaded objects here
    Return True
End Function