Stackoverflow exception - Recursive Treeview ASP.Net - asp.net

Question

I am trying to build a treeview recursively using VB.Net this is my code so far
.... Code to get the data table
For Each row As DataRow In dt.Rows
Dim oName As String = Nothing
Dim pId As String = Nothing
Dim cId As String = Nothing
Dim cmts As String = Nothing
Dim lvl As String = Nothing
oName = row(0)
pId = row(4)
cId = row(5)
If Not String.IsNullOrEmpty(row(3).ToString()) Then
cmts = row(3)
End If
lvl = row(2)
list.Add(New MyObject() With { _
.ObjectName = oName,
.ParentId = pId,
.ChildId = cId,
.Comments = cmts,
.level = lvl
})
Next
BindTree(list, Nothing)
End Sub
Private Sub BindTree(list As IEnumerable(Of MyObject), parentNode As TreeNode)
Dim nodes = list.Where(Function(x) If(parentNode Is Nothing, x.ParentId = "[Transform].[(Root)]", x.ParentId = parentNode.Value))
For Each node As MyObject In nodes
Dim newNode As New TreeNode(node.ObjectName, node.ParentId.ToString())
If parentNode Is Nothing Then
TreeView1.Nodes.Add(newNode)
Else
parentNode.ChildNodes.Add(newNode)
End If
BindTree(list, newNode)
Next
End Sub
also the new class
Public Class MyObject
Public ObjectName As String
Public ParentId As String
Public ChildId As String
Public Comments As String
Public level As Integer
End Class
The issue I am having is that when this goes so far through the recursion I get a System.StackOverFlowException. When looking at the exception snapshot every thing says "unable to evaluate expression" The error is coming from this line
Dim nodes = list.Where(Function(x) If(parentNode Is Nothing, x.ParentId = "[Transform].[(Root)]", x.ParentId = parentNode.Value)) but Ive no idea why or how to resolve it.
Any help would be very much appreciated.
Thanks
Simon

Answer 1

A StackOverflowException isn't thrown by a particular line of code, that's just the first line of code in the method being called which is overflowing the stack. And there isn't any more information that can really be given, because no further code can be executed. (Because the stack is full.)
Your method is recursive:
Private Sub BindTree(list As IEnumerable(Of MyObject), parentNode As TreeNode)
' ...
BindTree(list, newNode)
End Sub
Which is ok, except that you're not modifying the list variable anywhere. So every time you call the method, you call it with the same list. Therefore it will continue to perform the same logic, recursively, indefinitely, with no terminating condition.
Generally, you should think of a recursive method with the following structure (in VB-ish pseudo-code):
Method(ByVal something As SomeType)
' Check if the recursion should end
If SomeTerminatingCondition Then
Return
End If
' Perform the logic for this step of the recursion
DoSomething()
' Recurse again
Method(somethingModified)
End Method
It's not entirely clear to me from the code how list should be modified. But presumably when you call BindTree(list, newNode) at that point list should be some subset of the original list.