Removing items from a List(Of ) results in System.InvalidOperationException - vb.net

Question

It happens so often to me that I need to remove items from a List(Of) if a certain condition is met.
I prefer to do it this way:
For Each nClass As SomeClass In MyList
If (Something) Then
MyList.Remove(nClass)
End If
Next
However, when I remove an item, the collection is changed, and the For Next Statement can't proceed, and a System.InvalidOperationException is thrown.
I wonder if there's any general way to do this properly without writing big workarounds.
Can anybody tell how this should be done correctly?
I'm attaching a test code to see the error:
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim nList As New List(Of SomeClass)
For i As Integer = 0 To 5
Dim nNewItem As New SomeClass
nNewItem.Int = i
nNewItem.Text = "My text " + i.ToString
nList.Add(nNewItem)
Next
For Each nItem As SomeClass In nList
If nItem.Int > 1 And nItem.Int < 5 Then
nList.Remove(nItem)
End If
Next
End Sub
End Class
Public Class SomeClass
Private _iInt As Integer = 0
Private _sText As String = String.Empty
Public Property Int() As Integer
Get
Return _iInt
End Get
Set(value As Integer)
_iInt = value
End Set
End Property
Public Property Text() As String
Get
Return _sText
End Get
Set(value As String)
_sText = value
End Set
End Property
End Class

Answer 1

As Plutonix said, you need to work backwards through your loop -
Change
For Each nItem As SomeClass In nList
If nItem.Int > 1 And nItem.Int < 5 Then
nList.Remove(nItem)
End If
Next
to
For I As Integer = nList.Count to 0 Step -1
If nlist(I).Int > 1 And nList(I).Int < 5 Then
nList.RemoveAt(I)
End If
Next
The reason being that in a For Each..Next loop, the number of items in the object is recorded at the start of the loop and does not change. Even if you add or remove items in the object.
For example. Say you start off with a list of 10 letters.
A
B
C
D
E
F
G
H
I
J
So. At the start of your For Each loop, the number of items is recorded (10). As the loop iterates through the list, let's say you remove "E".
For the purpose of this explanation is doesn't matter too much which one. Anyway, you'll end up with all the subsequent items being moved back one. So what was at index position 5 will be at position 4 and so on to what was at index 10 is now at index 9 . The loop carries on and when it tries to access the item at index 10, it doesn't exist because it's outside the bounds of the list that now has 9 items.
If instead you use a `For..Next' loop stepping backwards, and start at the list item and head backwards, when you get to say, "E" and want to remove it, and then step backwards again and again until you get to the first item,the first item is still at the same index position, so no problem.