VB.NET for each loop not working

Question

I have a listbox that has x amount of object loaded from a txt file with this code:

    Dim lines() As String = IO.File.ReadAllLines(Application.StartupPath() + "\file.txt")
    List.Items.AddRange(lines)

    Try
        List.SelectedIndex = 0
    Catch ex As Exception

    End Try

    Return True

It loads them fine. Then I only try to loop through them like this:

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim num As Integer = 0
    Dim item As Object

    For Each item In List.Items
        List.SelectedIndex = num
        num += 1
    Next

End Sub

The error I get is this:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll

Additional information: List that this enumerator is bound to has been modified. An enumerator can only be used if the list does not change.

I tried to load the listbox manually, didn't help. Any help here?

But why loop it? Whats the point? Do you want to go trough every item and select it? — Fairy
– Fairy, Commented Aug 15, 2016 at 15:15
Yes. The point is to go through each item. Later I can then add something with it @Fairy — T1mpp4
– T1mpp4, Commented Aug 15, 2016 at 15:16

FloatingKiwi · Accepted Answer · 2016-08-15 15:40:19Z

2

Use

    For num = 0 To List.Items.Count - 1
        List.SelectedIndex = num
    Next

And as @CodyGray rightly pointed out: The reason for this is A for-each loop cannot be used if you're going to modify the collection of items you're enumerating over.

This will end up with the last item selected so it's only really of any use if you're testing out your event handlers for every item.

edited Aug 15, 2016 at 15:40

answered Aug 15, 2016 at 15:13

FloatingKiwi

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1 Comment

Cody Gray Over a year ago

You should explain why you have to do this. In other words, why your solution fixes the problem. (A for-each loop cannot be used if you're going to modify the collection of items you're enumerating over.)

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