treeview error

[tonycrew]

Hi all

Here's my code then i'll post my error.

Public Class Form1
    Dim lb1 As String
    Dim lb2 As String
    Public Class StringSift2
        Private maxOffset As Integer
        Public Sub New()
            Me.New(5)
        End Sub
        Public Sub New(ByVal maxOffset As Integer)
            Me.maxOffset = maxOffset
        End Sub
        Public Function Distance(ByVal s1 As String, ByVal s2 As String) As Single
            If [String].IsNullOrEmpty(s1) Then
                Return If([String].IsNullOrEmpty(s2), 0, s2.Length)
            End If
            If [String].IsNullOrEmpty(s2) Then
                Return s1.Length
            End If
            Dim c As Integer = 0
            Dim offset1 As Integer = 0
            Dim offset2 As Integer = 0
            Dim dist As Integer = 0
            While (c + offset1 < s1.Length) AndAlso (c + offset2 < s2.Length)
                If s1(c + offset1) <> s2(c + offset2) Then
                    offset1 = 0
                    offset2 = 0
                    For i As Integer = 0 To maxOffset - 1
                        If (c + i < s1.Length) AndAlso (s1(c + i) = s2(c)) Then
                            If i > 0 Then
                                dist += 1
                                offset1 = i
                            End If
                            GoTo ender
                        End If
                        If (c + i < s2.Length) AndAlso (s1(c) = s2(c + i)) Then
                            If i > 0 Then
                                dist += 1
                                offset2 = i
                            End If
                            GoTo ender
                        End If
                    Next
                    dist += 1
                End If
ender:
                c += 1
            End While
            Return dist + (s1.Length - offset1 + s2.Length - offset2) / 2 - c
        End Function

        Public Function Similarity(ByVal s1 As String, ByVal s2 As String) As Single
            Dim dis As Single = Distance(s1, s2)
            Dim maxLen As Integer = Math.Max(s1.Length, s2.Length)
            If maxLen = 0 Then
                Return 1
            Else
                Return 1 - dis / maxLen
            End If
        End Function
    End Class
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        FolderBrowserDialog2.ShowDialog()
        TextBox2.Text = FolderBrowserDialog2.SelectedPath
        If TextBox2.Text = "" Then
            TextBox4.Text = ""

        Else
            TextBox4.Text = ListBox2.Items.Count.ToString
            ListBox2.Items.AddRange(My.Computer.FileSystem.GetFiles(TextBox2.Text).ToArray)
            ListBox2.SelectedIndex = +1
            For i As Integer = 0 To Me.ListBox2.Items.Count - 1
                Dim fi As New IO.FileInfo(Me.ListBox2.Items(i))
                Me.ListBox2.Items(i) = Me.ListBox2.Items(i).ToString.Replace(fi.Directory.ToString & "\", "")
            Next
            lb2 = ListBox2.Items.IndexOf(ListBox2.SelectedItems)
        End If
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim MyObject As New StringSift2
        Dim ReturnVal As Single
        ReturnVal = MyObject.Distance(ListBox1.SelectedItem, ListBox2.SelectedItem)
        If ReturnVal = -1 Then
        End If
        TreeView1.Nodes(lb1).Nodes.Add(ReturnVal.ToString())

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        FolderBrowserDialog1.ShowDialog()
        TextBox1.Text = FolderBrowserDialog1.SelectedPath
        If TextBox1.Text = "" Then
            TextBox3.Text = ""

        Else
            TextBox3.Text = ListBox1.Items.Count.ToString
            ListBox1.Items.AddRange(My.Computer.FileSystem.GetFiles(TextBox1.Text).ToArray)
            ListBox1.SelectedIndex = +1
            For i As Integer = 0 To Me.ListBox1.Items.Count - 1
                Dim fi As New IO.FileInfo(Me.ListBox1.Items(i))
                Me.ListBox1.Items(i) = Me.ListBox1.Items(i).ToString.Replace(fi.Directory.ToString & "\", "")
            Next
            lb1 = ListBox1.Items.IndexOf(ListBox1.SelectedItems)
        End If
    End Sub
End Class

Object reference not set to an instance of an object.
on this line of code.

TreeView1.Nodes(lb1).Nodes.Add(ReturnVal.ToString())

Basically it's loading 2 dirs into 2 listbox's as strings then passing them through the Distance Function and then outputing the results into a treeview.

 

[jmcilhinney]

So you're getting an error message that is telling you that one of the references you're trying to use is Nothing. Which one is it? Is it TreeView1? Probably not. Is it TreeView1.Nodes. That's not possible. Is it TreeView1.Nodes(lb1)? Quite possible. This is what you need to do to debug your code. When you get a NullReferenceException you first need to determine which reference is Nothing, then work backwards to the point that you expected a value to be assigned. You can then take steps to work out why it wasn't or why that reference was lost later on.

 

[tonycrew]

ok thanks for the info i will try to work backwards then... and see where the problem may be.