Looping with List(of objects) in vb.net - vb.net

Question

I have a procedure in VB.net using VS.net 2008 which will get the list of Orders and build a XML file with the list of Orders as shown in the code below:
As the number of Orders is getting huge, I want to build the XML file for every 500 Orders
Dim Orders as List(of Orders)=DAL.GetAllOrders()
Dim Order as new Orders
Public xmlstring As New StringBuilder
If Not Orders Is Nothing Then
xmlstring.Append("<?xml version=""1.0"" encoding=""Windows-1252"" standalone=""yes""?>")
xmlstring.Append("<Orders>")
For Each Order In Orders
'Build the XML File
next
'access web service and pass the XML file
end if
Instead of building XML for all the records I want to create XML for each 500 records.
I tried the following code and it is throwing an error saying
Expression is of type Orders which is not a collection type.
Please help
Dim start As Integer
For i As Integer = start To Orders.Count Step 500
xmlstring.Append("<?xml version=""1.0"" encoding=""Windows-1252"" standalone=""yes""?>")
xmlstring.Append("<Orders>")
For Each Order In Orders(i)
'Build the XML File
next
next

Answer 1

Some issues to resolve:
Step 500 will SKIP 500 rows at a time. I.e., it will write Order #1, then order #501, then #1001, etc. You'll need to track your orders-per-count yourself.
Your use of variable names for Order/Orders vs. the class names is confusing, and is tripping you up.
XML should be built via the XML tools in .NET, not by string concat. You're going to build yourself into a brick wall quickly.
Loop construct:
Dim Orders as List(of Order) = DAL.GetAllOrders()
If Not Orders Is Nothing Then
Dim i As Integer = 1
For Each order As Order In Orders
If i=500 Then
' write XML footers, close the current file
' open the next file, write XML header
i = 1
Else
i += 1
End If
' write XML for this order
Next
' Write final XML footer and close current file
End If

Answer 2

it is throwing an error saying Expression is of type Orders which is not a collection type.
The variable "Orders" is a collection type (List(of Orders)), but Orders(i) is not, it is an "Orders" (whatever that is, you have not posted the definition) object.
So, you need to either implement IEnumerable in your Orders class or change this line:
For Each Order In Orders(i)

Answer 3

I would use something like this:
for i as integer = 0 to orders.count - 1
<create xml here and put into variable (append new XML as needed)>
if (i mod 500 = 0 andalso not i = 0) orelse i = orders.count - 1 then
<output XML here and clear XML variable>
end if
next i

Answer 4

How about something like this:
Dim OrdersList as List(of Orders)=DAL.GetAllOrders()
For i as int32 = 0 to OrdersList.Count() - 1
Dim o as Orders = OrdersList(i)
'Build your xml
If i mod 500 = 0 Then
'write out xml & reset your string builder
End If
Next
*Note I changed your Orders variable as the naming convention was a little confusing and might be causing name collisions.