' Declare writer
Private autoStreamWriter As StreamWriter
' Set file name as a constant value
Const FileName As String = "C:\Vehicles.txt"
 
' I use ValidateForm as a separate "form validator"
Private Function ValidateForm() As Boolean
  '
  If TextBox1.Text.Length = 0 Then
    MessageBox.Show("Model is empty. All fields must be entered before the information can be saved.")
    TextBox1.Focus() ' Move focus to missing field
    Return False
  End If
  ' Next Textboxes here
  ' Validation is Ok
  Return True
 
End Function
 
' Save button
Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
  '
  ' Check fields
  If Not ValidateForm() Then
    Exit Sub
  End If
 
  Try
    ' Create writer
    autoStreamWriter = New StreamWriter(FileName, True)
    autoStreamWriter.WriteLine(TextBox1.Text)
    autoStreamWriter.WriteLine(TextBox2.Text)
    ' Add missing WriteLine... here
    autoStreamWriter.Close()
    TextBox1.Clear()
    TextBox2.Clear()
    ' Add missing Clear... here
    ' Set focus to Model box
    TextBox1.Focus()
  Catch ex As Exception
    ' Handle exception
    ' Can't open file etc. can occur, so trap exceptions
  End Try
 
End Sub

' Data reader
Private autoStreamReader As StreamReader
Const FileName As String = "C:\Vehicles.txt"
 
' Structure to hold information for a one Auto object
Private Structure Auto
  Dim Model As String
  Dim Manufacturer As String
  Dim Year As String
  Dim VIN As Integer ' I did assume VIN is an integer number
End Structure
 
' Array of Auto objects
Private Autos() As Auto
' Number of items
Private AutoCount As Integer
 
' This "Read Data"-button
Private Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click
  ' Add similar Try...Catch...End Try here too (file can be missing etc.)
  Dim i As Integer
 
  ' Set count to -1 (no data)
  AutoCount = -1
  autoStreamReader = New StreamReader(FileName)
  ' Read the whole file
  Do Until autoStreamReader.EndOfStream
    ' Increase counter
    AutoCount += 1
    ' Redim array
    ReDim Preserve Autos(AutoCount)
    ' Read one Auto object
    Autos(AutoCount).Model = autoStreamReader.ReadLine
    Autos(AutoCount).Manufacturer = autoStreamReader.ReadLine
    Autos(AutoCount).Year = autoStreamReader.ReadLine
    Autos(AutoCount).VIN = CInt(autoStreamReader.ReadLine)
  Loop
  ' Fill a combo box with VINs
  For i = 0 To AutoCount
    ComboBox1.Items.Add(Autos(i).VIN)
  Next i
  '
End Sub
 
' A modified SelectedIndexChanged to select an Auto object and show its data
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
  ' Get selected Auto object
  Dim ThisAuto As Auto
 
  Try
    ThisAuto = Autos(ComboBox1.SelectedIndex)
    ' Place information in the labels
    Label1.Text = ThisAuto.Model
    ' and so on...
  Catch ex As Exception
    ' Handle exception
  End Try
 
End Sub