Checks The Informations In Text File. VB.NET - vb.net

Question

I work on a project "SignInLogeIn" using Visual Basic.NET.
I save the user informations in text file.
the name of the file is "data.txt".
to create a new account in my program. you must enter the name,email,password and the program write the informations in textfile.
i use "Streamwritter" to write the informations.
when user create a new account The program checks if the email entered by the user is already in the text file that contains the users' information.
and the program checks from informations by "StreamReader". it reads the information in text file and checks.
I have the problem.
when I CREATE A new account. problem appears.
and the problem is
"
An unhandled exception of type 'System.IO.IOException' occurred in mscorlib.dll
Additional information: The process cannot access the file 'D:\1- Anas Files\Projects\VisualBasic.NET\SignInLogIn\SignInLogIn\SignInLogIn\bin\Debug\Data.txt' because it is being used by another process.
"
I think the problem is that I used the file twice
Once to write and once to read.
The error occurs in this line "Dim sw As New StreamWriter("Data.txt")".
how can i solve this problem ?
this is the code of "SignIn" button
Private Sub btnSignIn_Click(sender As Object, e As EventArgs) Handles btnSignIn.Click
Dim strEmail As String = txtEmail.Text
Dim Reg As New Regex("^\w+([-_.]\w+)*#\w+([-.]\w+)*\.\w+([-.]\w+)*$")
If txtUserName.Text.Trim() = "" Or txtEmail.Text.Trim() = "" Or txtPassword.Text.Trim() = "" Then
MsgBox("Please Enter All Input")
If Not Reg.IsMatch(strEmail) Then
MsgBox("Please Enter Email")
End If
Else
Dim sr As New StreamReader("Data.txt")
Dim sw As New StreamWriter("Data.txt")
Dim strPerson As String = txtUserName.Text & ";" & txtEmail.Text & ";" & txtPassword.Text
Dim line As String = ""
Do
line = sr.ReadLine()
Dim arrData As String() = line.Split(";")
If arrData(1) = strEmail Then
MsgBox("Please Change Email")
Else
sw.WriteLine(strPerson)
sw.Close()
End If
Loop While line <> Nothing
sr.Close()
End If
End Sub

Answer 1

You open twice the same file. First, to read and second to write, this is why you cannot write.
Dim sr As New StreamReader("Data.txt")
Dim lines As String = sr.ReadToEnd().Split(Environment.NewLine)
sr.Close()
Dim strPerson As String = txtUserName.Text & ";" & txtEmail.Text & ";" & txtPassword.Text
Dim sw As New StreamWriter("Data.txt")
For Each line As String In lines
Dim arrData As String() = line.Split(";")
If arrData(1) = strEmail Then
MsgBox("Please Change Email")
Exit For
Else
sw.WriteLine(strPerson)
Exit For
End If
Next
sw.Close()

Answer 2

Streams need to be closed and disposed. They are usually put in Using blocks.
I wasn't quite sure of the program flow you wanted. It seemed, since you created a writer and a reader you intended to add to user to the file if they were not listed.
I broke out some of the code into separate methods. I used System.IO since we have a simple text file.
Private Sub btnSignIn_Click(sender As Object, e As EventArgs) Handles btnSignIn.Click
If ValidInput() Then
Dim strPerson As String = $"{txtUserName.Text};{txtEmail.Text};{txtPassword.Text}"
If Not IsUserInFile(strPerson) Then
File.AppendAllText("Data.txt", strPerson & Environment.NewLine)
End If
End If
End Sub
Private Function ValidInput() As Boolean
Dim strEmail As String = txtEmail.Text
Dim Reg As New Regex("^\w+([-_.]\w+)*#\w+([-.]\w+)*\.\w+([-.]\w+)*$")
If txtUserName.Text.Trim() = "" OrElse txtEmail.Text.Trim() = "" OrElse txtPassword.Text.Trim() = "" Then
MsgBox("Please Enter All Input")
Return False
If Not Reg.IsMatch(strEmail) Then
MsgBox("Please Enter Email")
Return False
End If
End If
Return True
End Function
Private Function IsUserInFile(Person As String) As Boolean
Dim p = Person.Split(";"c)
Dim lines = File.ReadAllLines("Data.txt")
For Each line In lines
If Person = line Then
Return True
End If
Dim fields = line.Split(";"c)
If fields(0) = p(0) AndAlso fields(2) = p(2) AndAlso fields(1) <> p(1) Then
MessageBox.Show("Please Change Email")
Return False
End If
Next
Return False
End Function
This is going to get messy and slow if there are too many users. This info should really be in a database. The worst thing is the passwords should always be salted and hashed; never stored as plain text even is a database.