求助串口程序编写

这几天刚刚接触VB2005，急需做一个串口通信的程序。研究了几天发现问题不少。因为以前只学过c编程。
先贴出我做的程序吧。
Imports System
Imports System.IO.Ports
Imports System.Threading

Public Class PortChat
    Shared _continue As Boolean
    Shared _serialPort As New SerialPort

    Public Shared Sub Main()
        '        Dim name As String
        '        Dim message As String
        Dim sComparer As StringComparer = StringComparer.OrdinalIgnoreCase
        '        Dim readThread As Thread = New Thread(AddressOf Read)

        ' Create a new SerialPort object with default settings.
        _serialPort = New SerialPort()
        ' Set the read/write timeouts
        _serialPort.ReadTimeout = 500
        _serialPort.WriteTimeout = 500
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Show all available COM ports.
        For Each sp As String In My.Computer.Ports.SerialPortNames
            ComboBox1.Items.Add(sp)
        Next
        ComboBox2.Items.Add("9600")
        ComboBox2.Items.Add("115200")
        ComboBox3.Items.Add("None")
        ComboBox3.Items.Add("Odd")
        ComboBox3.Items.Add("Even")
        ComboBox3.Items.Add("Mark")
        ComboBox3.Items.Add("Space")
        ComboBox4.Items.Add("5")
        ComboBox4.Items.Add("6")
        ComboBox4.Items.Add("7")
        ComboBox4.Items.Add("8")
        ComboBox5.Items.Add("1")
        ComboBox5.Items.Add("2")
    End Sub
    '打开串口
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If (ComboBox1.Text <> "") Then
            _serialPort.PortName = ComboBox1.Text
        Else
            _serialPort.PortName = "COM1"
        End If
        If (ComboBox2.Text <> "") Then
            _serialPort.BaudRate = ComboBox2.Text
        Else
            _serialPort.BaudRate = 9600
        End If
        Select Case ComboBox3.Text
            Case "None"
                _serialPort.Parity = 0
            Case "Odd"
                _serialPort.Parity = 1
            Case "Even"
                _serialPort.Parity = 2
            Case "Mark"
                _serialPort.Parity = 3
            Case "Space"
                _serialPort.Parity = 4
            Case Else
                _serialPort.Parity = 0
        End Select
        If (ComboBox4.Text <> "") Then
            _serialPort.DataBits = ComboBox4.Text
        Else
            _serialPort.DataBits = 8
        End If
        If (ComboBox5.Text <> "") Then
            _serialPort.StopBits = ComboBox5.Text
        Else
            _serialPort.StopBits = 1
        End If
        If _serialPort.IsOpen Then
            TextBox1.Text = "此串口已打开"
        Else
            _serialPort.Open()
        End If
    End Sub
    '关闭串口
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        _serialPort.Close()
    End Sub
End Class

现在简单的实现了打开和关闭串口。但是无法检测已关闭的串口。看资料中说使用If _serialPort.IsOpen Then可以实现，但是我时间测试无论串口是否被打开，_serialPort.IsOpen的返回值都是false，还有就是如何获取异常信息。就像我打了已经打开的串口程序就会死掉。如何获取这样的异常信息并显示出来保证程序不死。 --------------------编程问答-------------------- _serialPort.IsOpen它只能检测到自己打开的串口状态吗？就是我用其他的串口助手打开了COM1，再执行这个程序这里就无法检测到串口是打开的了。返回值仍然是false，如何才能检测到计算机中其他程序打开的串口啊？ --------------------编程问答-------------------- 首先判断串口是否打开，然后在设置端口，就不会有问题了
推荐一段代码：
  If SerialPort1.IsOpen Then
            SerialPort1.Close()
        End If
        Try
            With SerialPort1
                .PortName = ComboBox1.Text
                .BaudRate = 19200
                .DataBits = 8
                .Parity = Parity.Odd
                .StopBits = StopBits.One
            End With
            SerialPort1.Open()
            Me.messagelab1.Text = ComboBox1.Text & "  " & "Connected" & "  "
            Catch ex As Exception
            MsgBox(ex.ToString)
        End Try

补充：.NET技术 ,  VB.NET