Selected Listbox Items - to add data to array VB.net

Question

Struggling to test which Listbox items are selected. I want to allow the user to select multiple items in a listbox so that a string can be stored in an array where the list is also stored. It is a rollcall system (a task for my Year 10 students). I just can't get the syntax right for the listbox. The Listbox is set to MultiSelection.

BTW

If Listbox.SelectedItem = true Then

Does not work. It returns an error.

My code below returns the first selected item (in a message box)- but not the others. I'm just going round and round now. there must be an easier way. Thoughts?

Private Sub BtnRollCall1_Click(sender As Object, e As EventArgs) Handles btnRollCall1.Click
    Dim ExcursionArray(29, 4) As String
    Dim selected As Integer
    Dim LoadNames As StreamReader = File.OpenText("ClassList.txt")
    For i = 0 To 29
        ExcursionArray(i, 0) = (LoadNames.ReadLine())
        lbxRollCall.Items.Add(ExcursionArray(i, 0))
    Next

    For Each SelectedItem As string In lbxRollCall.SelectedItems
        selected = lbxRollCall.SelectedIndex
        ExcursionArray(selected, 1) = "a"
    Next

    For x = 0 To 29
        If (ExcursionArray(x, 1) = "a") Then
            MsgBox(ExcursionArray(x, 0))
        End If

    Next
End Sub

Answer 1

It appears that what you actually want to do is update a 2D array and set the second 'column' to "a" if the corresponding 'row' is selected in the ListBox. One way to do that would be like so:

For Each selectedIndex In lbxRollCall.SelectedIndices
    ExcursionArray(selectedIndex, 1) = "a"
Next

Another option would be like so:

For i = 0 To ExcursionArray.GetUpperBound(0)
    If lbxRollCall.GetSelected(i) Then
        ExcursionArray(i, 1) = "a"
    End If
Next