Could someone explain where are the errors in this code in vb.net - vb.net

Question

I'm new to this site and also a newbee in vb.net, I created a simple form in vb.net, a form with 3 buttons, by clicking Button1 Species1.txt is created, and by clicking Button2 the lines in Species1.txt are copied in a String Array called astSpecies(), and by Button3 the String Array is copied in a new file, named Species2.txt, below is the code.
Public Class Form4
Dim astSpecies() As String
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim myStreamWriter = New StreamWriter("C:\Users\Administrator\Documents\species1.txt", True)
myStreamWriter.WriteLine("Pagasius pangasius")
myStreamWriter.WriteLine("Meretrix lyrata")
myStreamWriter.WriteLine("Psetta maxima")
myStreamWriter.WriteLine("Nephrops norvegicus")
myStreamWriter.WriteLine("Homarus americanus")
myStreamWriter.WriteLine("Procambarus clarkii")
myStreamWriter.Close()
MsgBox("list complete")
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim myStreamReader = New StreamReader("C:\Users\Administrator\Documents\species1.txt")
Dim i As Integer
Dim stOutput As String
stOutput = ""
Do While Not myStreamReader.EndOfStream
astSpecies(i) = myStreamReader.ReadLine
stOutput = stOutput & astSpecies(i) & vbNewLine
i = i + 1
Loop
myStreamReader.Close()
MsgBox(stOutput)
End Sub
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim myStreamWriter = New StreamWriter("C:\Users\Administrator\Documents\species2.txt", True)
Dim o As Integer
Do While o <= astSpecies.Length
myStreamWriter.WriteLine(astSpecies(o))
o = o + 1
Loop
myStreamWriter.Close()
End Sub
End Class

Answer 1

First of all, you should make a few settings when it comes to VB.Net. 1.) set Option Strict to On 2.) remove the VB6 namespace. VB6 is the old Visual Basic. There are many functions in this that are inefficient from today's perspective. So please do not write MsgBox() but MessageBox.Show("").
(If you still need control characters such as NewLine or Tab, you can set a selective reference with Imports Microsoft.VisualBasic.ControlChars. Sounds contradictory, but it is useful, because why should you also write ChrW(9), it is not legible.)
I quickly started a project myself and wrote whatever you wanted.
I still don't quite understand why you first write things into a text file, then read them out, and then write that into a second text file – I want to say: where do the strings originally come from? The strings must have been there already? Anyway, I filled a List(of String) in the Button2_Click procedure. This has the advantage that you don't have to know in advance how many strings are coming, and you can sort them later and so on ...
You should also discard all Writers when you no longer need them. So use Using. Otherwise it can happen that the written files are not discarded and you can no longer edit the file.
Imports Microsoft.VisualBasic.ControlChars
Imports Microsoft.WindowsAPICodePack.Dialogs
Public NotInheritable Class FormMain
Private Path As String = ""
Private allLines As New List(Of String)
Private Sub FormMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.BackColor = Color.FromArgb(161, 181, 165)
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Using OFolderD As New CommonOpenFileDialog
OFolderD.Title = "Ordner auswählen"
OFolderD.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Desktop)
OFolderD.IsFolderPicker = True
If OFolderD.ShowDialog() = CommonFileDialogResult.Ok Then
Path = OFolderD.FileName
Else
Return
End If
End Using
Path &= "\Data.txt"
Using txtfile As System.IO.StreamWriter = My.Computer.FileSystem.OpenTextFileWriter(Path, True)
txtfile.WriteLine("Pagasius pangasius")
txtfile.WriteLine("Meretrix lyrata")
txtfile.WriteLine("Psetta maxima")
txtfile.WriteLine("Nephrops norvegicus")
txtfile.WriteLine("Homarus americanus")
txtfile.WriteLine("Procambarus clarkii")
txtfile.Close()
End Using
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
'read all Text
Dim RAT() As String = System.IO.File.ReadAllLines(Path, System.Text.Encoding.UTF8)
If RAT.Length = 0 OrElse RAT.Length = 1 Then
MessageBox.Show("The File only contains 0 or 1 characters.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Hand)
Return
End If
allLines.AddRange(RAT)
End Sub
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim Pfad_txt As String = Path.Substring(0, Path.LastIndexOf("\"c)) & "\Data2.txt"
Using txtfile As System.IO.StreamWriter = My.Computer.FileSystem.OpenTextFileWriter(Pfad_txt, True)
For Each Line As String In allLines
txtfile.WriteLine(Line)
Next
txtfile.Close()
End Using
End Sub
End Class
By the way: I use a FolderBrowserDialog in the Button1_Click procedure. This should be done so that the program also runs properly on other PCs. In order to be able to use the FBD, you have to download Microsoft.WindowsAPICodePack.Dialogs in Visual Studio's own Nuget package manager.
how to set Option Strict to On
How to uncheck VB6.
how to install FolderBrowserDialog in Visual Studio

Answer 2

Button1
If you want to use a StreamWriter it should be disposed. Classes in the .net Framework that have a Dispose method may use resources outside of the framework which need to be cleaned up. The classes shield you from these details by provided a Dispose method which must be called to properly do the clean up. Normally this is done with Using blocks.
I used a string builder which saves creating and throwing away a string each time you change the string. You may have heard that strings are immutable (cannot be changed). The StringBuilder class gets around this limitation. It is worth using if you have many changes to your string.
The File class is a .net class that you can use to read or write files. It is not as flexible as the stream classes but it is very easy to use.
Button 2
When you declared your Array, you declared an array with no elements. You cannot add elements to an array with no space for them. As Daniel pointed out, you can use the .net class List(Of T) The T stands for Type. This is very good suggestion when you don't know the number of elements in advance. I stuck with the array idea by assigning the array returned by File.ReadAllLines to the lines variable.
You get the same result by simply reading all the text and displaying it.
Button 3
Again I used the File class here which allows you to complete your task in a single line of code. Using 2 parameters for the String.Join method, the separator string and the array to join, we reproduce the original file.
Private SpeciesPath As String = "C:\Users\maryo\Documents\species1.txt"
Private lines As String()
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim sb As New StringBuilder
sb.AppendLine("Pagasius pangasius")
sb.AppendLine("Meretrix lyrata")
sb.AppendLine("Psetta maxima")
sb.AppendLine("Nephrops norvegicus")
sb.AppendLine("Homarus americanus")
sb.AppendLine("Procambarus clarkii")
File.WriteAllText(SpeciesPath, sb.ToString)
MsgBox("list complete")
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
lines = File.ReadAllLines(SpeciesPath)
MessageBox.Show(String.Join(Environment.NewLine, lines))
'OR
MessageBox.Show(File.ReadAllText(SpeciesPath))
End Sub
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
File.WriteAllLines("C:\Users\maryo\Documents\species2.txt", lines))
End Sub