How to pass parameters to delegate (C#, VB) into loop - vb.net

Question

I have function with loop
Sub KvmActionForEachVm(CN As MySqlConnection, SshClient As Renci.SshNet.SshClient, Action As Action(Of MySqlConnection, Renci.SshNet.SshClient, String, Integer))
Dim AdmVMList As List(Of AdmVM) = ReadAdmVMList(CN)
For Each One As AdmVM In AdmVMList
Try
Action.Invoke(CN, SshClient, One.Name, CInt(One.Id))
'for example ParseVmConfig(CN, SshClient, One.Name, One.Id)
Catch ex As Exception
Console.WriteLine(One.Name & ": " & ex.Message)
Continue For
End Try
Next
SshClient.Disconnect()
End Sub
and various function with the same signature what can be working in loop like below. Of course, this function require correct VmName(One.Name) and VmId(One.Id)
Sub ParseVmConfig(CN As MySqlConnection, SshClient As Renci.SshNet.SshClient, VmName As String, VmId As Integer)
....
End sub
Without loop I'm usually pass delegates as parameters by the same way
KvmActionForEachVm(CN, SshClient, Sub() ParseVmConfig(CN, SshClient, "", 0))
But in this case I'm confused.
Upd. I'm using NET Core 5.0 and this is screen of my application with this issue.

Answer 1

You didn't indicate which version of .NET / VB you're using. In old versions of .NET, there is an interesting behavior of capture in a loop. It arises from the intersection of the scope of the loop control variable (which is the entire loop, not just an individual iteration) and the fact that variables from the enclosing scope of the lambda are captured by reference and not by value. This can lead to surprising behavior.
If this is the issue you're having (every invocation of the new Action runs as if called by the last loop iteration, or even one past the last loop iteration), then you can fix it by declaring new variables within the loop scope to capture. These variables are scoped by the loop iteration, vs. the loop variable which can have a weird scope of all loop iterations.
e.g.
For Each One As AdmVM In AdmVMList
Dim vmName = One.Name
Dim vmId = One.Id
Call Foo(Sub() Action.Invoke(CN, SshClient, vmName, vmId)
Next
This surprising behavior was addressed in a fairly old version of C# (by making each iteration of the loop get a new copy of the loop control variable), and I'm not sure what its history may be in VB. I would imagine that it was cleaned up ca. 2010 as VB was kept fairly close to C# in that time period, but maybe you're using a very old version of VB, or maybe my imagination is wrong.
Also see:
Related C# question: Lambda variable capture in loop - what happens here?
Eric Lippert on the issue in C# (1): https://ericlippert.com/2009/11/12/closing-over-the-loop-variable-considered-harmful-part-one/
Eric Lippert on the issue in C# (2):
https://ericlippert.com/2009/11/16/closing-over-the-loop-variable-considered-harmful-part-two/