How to read a specific line from a text file in VB - vb.net

Question

I am creating a program that is supposed to write text into a text file, and should be able to read specific lines from a text file in VB (so if i needed to read a specific name I could select line 5 and it would display in the textbox). I am able to read the text from the text file but I do not know how to control a specific line.
Here is my code:
Public Class Form1
Private Sub btnSubmit_Click(sender As System.Object, e As System.EventArgs) Handles btnSubmit.Click
Dim writer As New System.IO.StreamWriter("/text.txt", True)
writer.WriteLine(txtFirstName.Text)
writer.WriteLine(txtLastName.Text)
writer.WriteLine("-------------------------------------")
writer.Close()
End Sub
Private Sub btnRead_Click(sender As System.Object, e As System.EventArgs) Handles btnRead.Click
Dim reader As New System.IO.StreamReader("/text.txt")
Dim FirstName, LastName As String
FirstName = reader.ReadLine()
LastName = reader.ReadLine()
reader.Close()
txtFirstName.Text = FirstName
txtLastName.Text = LastName
End Sub
Private Sub btnClear_Click(sender As System.Object, e As System.EventArgs) Handles btnClear.Click
txtFirstName.Clear()
txtLastName.Clear()
End Sub
End Class
Any help would be appreciated. Thanks!

Answer 1

You will have to read all lines up to the one you're interested in. For example:
Function ReadLineWithNumberFrom(filePath As String, ByVal lineNumber As Integer) As String
Using file As New StreamReader(filePath)
' Skip all preceding lines: '
For i As Integer = 1 To lineNumber - 1
If file.ReadLine() Is Nothing Then
Throw New ArgumentOutOfRangeException("lineNumber")
End If
Next
' Attempt to read the line you're interested in: '
Dim line As String = file.ReadLine()
If line Is Nothing Then
Throw New ArgumentOutOfRangeException("lineNumber")
End If
' Succeded!
Return line
End Using
End Function
This is because lines of text are variable-length records, and there is no way to guess the exact file offset where a specific line begins — not without an index.
If you frequently need to load a specific line, you have some more options:
Load the complete text file into memory, e.g. by using File.ReadAllLines("Foobar.txt"). This returns a String() array which you can access by line number directly.
Create a line number index manually. That is, process a text file line by line, and fill a Dictionary(Of Integer, Integer) as you go. The keys are line numbers, and the values are file offsets. This allows you to .Seek right to the beginning of a specific line without having to keep the whole file in memory.

Answer 2

Try this:
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
Dim reader As New System.IO.StreamReader("C:\text.txt")
Dim allLines As List(Of String) = New List(Of String)
Do While Not reader.EndOfStream
allLines.Add(reader.ReadLine())
Loop
reader.Close()
txtFirstName.Text = ReadLine(5, allLines)
txtLastName.Text = ReadLine(6, allLines)
End Sub
Public Function ReadLine(lineNumber As Integer, lines As List(Of String)) As String
Return lines(lineNumber - 1)
End Function
If you had a file with this:
Line 1
Line 2
Line 3
Line 4
My Name
My LastName
your name textbox will have 'My Name' and your LastName textbox will have 'My LastName'.

Answer 3

This is very simple, try this:
Dim strLineText As String
Dim intLineNumber As Integer
LineNumber=3
myLine = File.ReadAllLines("D:\text.txt").ElementAt(LineNumber).ToString

Answer 4

Yet another option
Private Function readNthLine(fileAndPath As String, lineNumber As Integer) As String
Dim nthLine As String = Nothing
Dim n As Integer
Try
Using sr As StreamReader = New StreamReader(fileAndPath)
n = 0
Do While (sr.Peek() >= 0) And (n < lineNumber)
sr.ReadLine()
n += 1
Loop
If sr.Peek() >= 0 Then
nthLine = sr.ReadLine()
End If
End Using
Catch ex As Exception
Throw
End Try
Return nthLine
End Function

Answer 5

i tried this and it works fine. using VB Express
content inside test.txt:
line1
line2
1
John
then in the form i add
textbox1
textbox2
label1
label2
and a button.
code inside the button:
Private Sub Button2_Click_1(sender As Object, e As EventArgs) Handles Button2.Click
Dim myLine As String
Dim lineNumber0 As Integer
lineNumber0 = 0
Dim lineNumber1 As Integer
lineNumber1 = 1
Dim lineNumber2 As Integer
lineNumber2 = 2
Dim lineNumber3 As Integer
lineNumber3 = 3
TextBox1.Text=File.ReadAllLines("D:\test.txt").ElementAt(lineNumber0).ToString
TextBox2.Text=File.ReadAllLines("D:\test.txt").ElementAt(lineNumber1).ToString
Label1.Text = File.ReadAllLines("D:\test.txt").ElementAt(lineNumber2).ToString
Label2.Text = File.ReadAllLines("D:\test.txt").ElementAt(lineNumber3).ToString
End Sub

Answer 6

Here's a simple but effective solution:
Dim Reader As String = System.IO.File.ReadAllLines("C:\File.txt")(1)
MsgBox("Line 1: " + Reader)
The MsgBox should show the first line of C:\File.txt.