Null Reference Exception when reading file vb.NET - vb.net

Question

So I am creating a program that needs to be able to read line by line from a .cfg (config) file, it can open it happily; here is the code:
OpenConfig.ShowDialog()
file = OpenConfig.FileName()
fileReader()
However when it tries to read the file, using this code:
Function fileReader()
Dim reader As New StreamReader(file)
Dim vLb As ListBox = shopTabs.SelectedTab.Controls.Item(10) 'Listbox Variable
For i = 0 To reader.Peek
textline(i) = reader.ReadLine()
vLb.Items.Add(i)
Next
Return True
End Function
It throws an exception at the line:
textline(i) = reader.ReadLine()
Any help would be greatly appreciated as I can't work out why it does so.

Answer 1

Your code could be simplified into the following code:
Using openConfig As New OpenFileDialog()
If openConfig.ShowDialog(Me) = DialogResult.OK Then
For Each s As String In File.ReadAllLines(openConfig.FileName)
ListBox1.Items.Add(s)
Next
End If
End Using
As I commented, your code does some things that are highly questionable and undoubtedly difficult to maintain, such as referencing a control by the index property.
I suspect that your project would benefit from using UserControls too, since I'm guessing you have the same controls placed in every tab (a ListBox is always control index #10?).