Hello, everyone!
I write a program with serial port, error happend--The I/O operation has been aborted because of either a thread exit or an application request. I have no idea with it.

This is my source code.
Imports System
Imports System.Data
Imports System.Windows.Forms
Imports System.IO
Imports System.IO.Ports

Public Class Form1

   Dim WithEvents port As New IO.Ports.SerialPort("COM1", 9600, Parity.None, 8, StopBits.One)

   Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
       Try
           port.ReceivedBytesThreshold = 1
           If port.IsOpen = True Then
               port.Close()
           End If
           port.Open()
           lblError.Text = "COM1 port connected!"
           lblError.ForeColor = Color.Green
           TextBox1.Text = "0.000kg"
       Catch ex As Exception
           lblError.Text = ex.Message
       End Try
   End Sub

   Private Sub port_DataReceived1(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived
       Try
           TextBox1.Invoke(New myDelegate(AddressOf updateTextBox), New Object() {})
       Catch ex As System.IO.IOException
           MsgBox(ex.Message)
       End Try

   End Sub

   '------------------------------------------------------
   ' Delegate and subroutine to update the Textbox control
   '------------------------------------------------------
   Public Delegate Sub myDelegate()
   Public Sub updateTextBox()
       Dim tmpStr As String
       Dim pos As Integer
       tmpStr = Trim(port.ReadLine)
       pos = InStr(tmpStr, "GS")
       If pos > 0 Then
           tmpStr = Trim(Mid(tmpStr, pos + 2))
           If tmpStr <> Trim(TextBox1.Text) Then
               With TextBox1
                   .Text = tmpStr
                   '.ScrollToCaret()
               End With
           End If

       End If
   End Sub

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       port.Close()
       Me.Close()
   End Sub
End Class