Sorting through a list box

Here's the situation, I have a listbox that contains names in this format "last name, first name". I also have a textbox that the user types can type a string to pull up the appropiate name, i.e. if the user types in "S" I want the listbox to move to the "S" section, or even better only display names that start with "S".

"Smith, Ro" would bring up "Smith, Robert" (or any other Smith with a first name that starts with "Ro". I'm not sure how I can accomplish this and not kill program response time. The listbox could contain any number of items (probably less than 100, but upwards of 100 is possible.

Another question, how many items can a listbox hold without a serious slow down in response time?:confused:

It seems like there should be some form of intrinsic way to do this, but I only found how to find an exact match (of course I didn't look THAT hard). But if you don't find one then this works just fine:

VB Code:

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'make an array and fill listbox
        Dim items() As String = {"Marquez, Ed", "Marcus, Allen", "Sarver, Mike", "Doran, Cookie", "Dorn, Mike"}
        ListBox1.Items.AddRange(items)
    End Sub
 
    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        'convert listbox item to string array and pass to function
        Dim itms(ListBox1.Items.Count - 1) As String
        ListBox1.Items.CopyTo(itms, 0)
        ListBox1.SelectedIndex= ClosestIndexOf(TextBox1.Text, itms, False)
    End Sub
 
    Private Function ClosestIndexOf(ByVal Text As String, ByVal Items() As String, Optional ByVal CaseSensitive As Boolean = True) As Integer
        'returns -1 if no match at all is found
        Dim itm As String
        Dim found As Integer = -1
        For Each itm In Items
            If CaseSensitive Then
                If itm.StartsWith(Text) Then
                    found = Array.IndexOf(Items, itm)
                    Exit For
                End If
            Else
                'make both lower case before testing
                Dim tmp As String = itm.ToLower
                If tmp.StartsWith(Text.ToLower) Then
                    found = Array.IndexOf(Items, itm)
                    Exit For
                End If
            End If
        Next
        Return found
    End Function

Thank You!
Actually it is finding the closest match, i.e. Smi would go to Smith. Thanks for the code sample.

Yeah I wrote that because I figured it'd come in handy for me too at some point, but the intrinsic IndexOf function will find an exact match if you need that.