为什么我这个BkWorker.CancelAsync()不管用，停止不了呢？？

yeliqin123 2009-05-11 04:25:14



Imports System

Imports System.Windows.Forms

Imports System.Drawing

Imports System.IO.Ports

Imports System.Text







Public Class Form_main

    Dim rs232 As SerialPort

    Dim comflag As Boolean

    Delegate Sub SetTextCallback(ByVal InputString As String)





    Private Sub Form_main_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load



        With Me

            .AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi

            .StartPosition = FormStartPosition.CenterScreen

            .WindowState = FormWindowState.Maximized

            .MaximizeBox = True

            .MinimizeBox = True

            .AutoScroll = True

        End With

        For Each sp As String In SerialPort.GetPortNames

            TStripCmbCOM.Items.Add(sp)

        Next

        TStripCmbCOM.Sorted = False

        TStripCmbCOM.SelectedIndex = 0

        comflag = False

        com_flag()



    End Sub

    Sub int_com()

        Dim mbaudrate As Integer

        Dim mparity As Parity

        Dim mdatabit As Integer

        Dim mstopbit As StopBits

        Dim mportname As String



        mportname = TStripCmbCOM.SelectedItem.ToString

        mbaudrate = 9600

        mparity = Parity.None

        mdatabit = 8

        mstopbit = StopBits.Two

        rs232 = New SerialPort(mportname, mbaudrate, mparity, mdatabit, mstopbit)

    End Sub

    Sub com_flag()

        If comflag = True Then



            TStripBtnOnLine.Enabled = False

            TStripBtnDownLine.Enabled = True

        Else



            TStripBtnOnLine.Enabled = True

            TStripBtnDownLine.Enabled = False

        End If

    End Sub











    Private Sub TStripBtnOnLine_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles TStripBtnOnLine.Click

        'rs232.ReceivedBytesThreshold = 1

        int_com()

        rs232.Encoding = Encoding.Default

        If Not rs232.IsOpen Then

            rs232.Open()

            comflag = True

            com_flag()

            BkWorker.WorkerSupportsCancellation = True

            BkWorker.RunWorkerAsync()



        Else

            MsgBox("通信端口打开错误 ", MsgBoxStyle.Critical Or MsgBoxStyle.OkCancel)

            End

        End If





    End Sub



    Private Sub BkWorker_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BkWorker.DoWork

        'GetRs232Data()

        System.Threading.Thread.Sleep(1000)

        If BkWorker.CancellationPending Then

            e.Cancel = True

            Return



        End If



        GetRs232Data()

    End Sub

    Private Sub GetRs232Data()

        Dim instring As String

        instring = ""

        If Not rs232.IsOpen Then Exit Sub

        Try

            rs232.ReadTimeout = 1000

            instring = rs232.ReadExisting()

            If instring.Length = 0 Then

                Exit Sub

            Else

                DisplayText(instring)



            End If





        Catch ex As Exception

            MessageBox.Show("读取错误" + ex.ToString, "错误提示", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)



        End Try

    End Sub

    Private Sub DisplayText(ByVal comdata As String)

        If Me.TxtDisplay.InvokeRequired Then

            Dim d As New SetTextCallback(AddressOf DisplayText)

            Me.Invoke(d, New Object() {comdata})

        Else

            Me.TxtDisplay.Text += comdata



        End If

    End Sub



    Private Sub BkWorker_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BkWorker.RunWorkerCompleted

        If Not BkWorker.CancellationPending Then

            BkWorker.RunWorkerAsync()

        End If

    End Sub



    Private Sub TStripBtnDownLine_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles TStripBtnDownLine.Click

        If rs232 Is Nothing OrElse Not rs232.IsOpen Then

            MsgBox("通信端口尚未打开", MsgBoxStyle.Critical Or MsgBoxStyle.OkCancel)

        Else

            'rs232.ReceivedBytesThreshold = 0

            BkWorker.Dispose()

            BkWorker.CancelAsync()

            comflag = False

            com_flag()

            rs232.Close()

        End If





    End Sub

End Class