How to browse from bottom to top of a text file in vb.net? - vb.net

Question

I cannot get my code below to work correctly, in fact I want to press a back button in order to go up the lines one by one of a text file then I cut the chain into 3 parts.
Dim LinesOfText() As String = System.IO.File.ReadAllLines("c:\essai.librairie", Encoding.UTF8)
For line As Integer = LinesOfText.Length - 1 To 0 Step -1
Dim currentLine As String = LinesOfText(line)
Dim value As String = currentLine
Dim startIndex As Integer = 0
Dim length As Integer = 17
Dim substring As String = value.Substring(startIndex, length)
Dim subs As String = value.Substring(17, 90)
Dim subst As String = value.Substring(107, 120)
TextBox1.Text = substring
TextBox2.Text = subs
TextBox3.Text = subst
Next

Answer 1

If you store the lines and a line counter so that they are in scope where needed, you can do it like this:
Imports System.IO
Public Class Form1
Dim lines As String()
Dim currentLine As Integer = -1
Sub LoadData(filename As String)
lines = File.ReadAllLines(filename)
currentLine = lines.Length - 1
End Sub
Sub ShowCurrentLine()
If currentLine >= 0 Then
TextBox1.Text = lines(currentLine).Substring(0, 3)
TextBox2.Text = lines(currentLine).Substring(4, 3)
TextBox3.Text = lines(currentLine).Substring(8, 3)
lblLineNo.Text = (currentLine + 1) & "/" & lines.Length
Else
TextBox1.Clear()
TextBox2.Clear()
TextBox3.Clear()
lblLineNo.Text = "-"
End If
End Sub
Private Sub bnNext_Click(sender As Object, e As EventArgs) Handles bnNext.Click
If currentLine < lines.Length - 1 Then
currentLine += 1
ShowCurrentLine()
End If
End Sub
Private Sub bnPrev_Click(sender As Object, e As EventArgs) Handles bnPrev.Click
If currentLine > 0 Then
currentLine -= 1
ShowCurrentLine()
End If
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
LoadData("C:\temp\SO67209265.txt")
ShowCurrentLine()
End Sub
End Class
You will need to set the substring parameters for your data—I just used a small text file—and the filename to be loaded.
The label lblLineNo is used to show the current line number, starting at 1.