vb.net - VB.net 停止后台工作者

Question

我想创建一个按钮，可以停止我的后台工作人员并结束它正在处理的所有进程。

这是我的示例 backgroundworker 代码：

       Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

            Try
                If BackgroundWorker1.IsBusy <> True Then
                    BackgroundWorker1.RunWorkerAsync()
                End If
            Catch ex As Exception
            End Try

        End Sub

        Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

            Dim counter As Integer = 1

            Do

            'updated code with stop function----------------
            BackgroundWorker1.WorkerSupportsCancellation = True
            If BackgroundWorker1.CancellationPending Then
                e.Cancel = True
                ProgressBar1.Value = 0
                Exit Do
            End If
            'updated code with stop function----------------

            ListBox1.Items.Add(counter)

            ProgressBar1.Value = ((counter - 1) / limit) * 100
            counter = counter + 1
            Loop While(counter <= 999999999999999999)

        End Sub

        Private Sub BackgroundWorker1_ProgressChanged(sender As System.Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
            Try
            Catch ex As Exception
            End Try
        End Sub

        Private Sub BackgroundWorker1_Completed(sender As System.Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
            Try
            Catch ex As Exception
            End Try
        End Sub

        Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
            System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = False    
        End Sub

        'updated code with stop function----------------
        Private Sub StopButton_Click(sender As Object, e As EventArgs) Handles StopButton.Click
              If BackgroundWorker1.IsBusy Then

                  If BackgroundWorker1.WorkerSupportsCancellation Then                
                     BackgroundWorker1.CancelAsync()
                  End If
              End If
        End Sub
        'updated code with stop function----------------

当我停止后台工作程序时，我想重置循环并将进度条返回到 0%。

这可能吗？

---

上面的代码已经更新，现在可以正常工作了。

我在我的 do 循环中添加了这段代码：

        BackgroundWorker1.WorkerSupportsCancellation = True
        If BackgroundWorker1.CancellationPending Then
            e.Cancel = True
            ProgressBar1.Value = 0
            Exit Do
        End If

我创建了一个停止工作人员的按钮：

    Private Sub StopButton_Click(sender As Object, e As EventArgs) Handles StopButton.Click
          If BackgroundWorker1.IsBusy Then

              If BackgroundWorker1.WorkerSupportsCancellation Then                
                 BackgroundWorker1.CancelAsync()
              End If
          End If
    End Sub

Answer 1

Backgroundworker 类具有CancelAsync()您需要调用以取消执行 bgw 的方法。

您需要将该Backgroundworker.WorkerSupportsCancellation属性设置为 true 并且在 while 循环内您需要检查该CancellationPending属性的值是否true指示对该方法的调用CancelAsync()。

如果CancellationPending计算结果为真，您将（您应该已经这样做）调用重载ReportProgress()( Docu ) 方法之一来将 ProgressBar 值设置为所需值。

编辑：您应该将Cancel属性设置DoWorkEventArgs为 true，以便检查事件内部的Cancelled属性。RunWorkerCompletedEventArgsRunworkerCompleted

您也不应该访问驻留在 UI 线程中的任何控件。您最好使用ProgressChanged( Docu ) 事件。

请参阅：BackgroundWorker 文档

Answer 2

Public Class Form1
    Private iVal As Integer = 0
    Private Sub bgw_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgw.DoWork
        For iVal = iVal To 100 Step 1
            bgw.ReportProgress(iVal)
            Threading.Thread.Sleep(99)
            If (bgw.CancellationPending = True) Then
                e.Cancel = True
                Exit For
            End If
        Next
    End Sub

    Private Sub bgw_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles bgw.ProgressChanged
        pbar.Value = e.ProgressPercentage
        lblProgrss.Text = e.ProgressPercentage.ToString() & "%"
    End Sub

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

        If (e.Cancelled = True) Then
            pic.Visible = False
            pbar.Value = iVal
            lblProgrss.Text = iVal & "%"
            btnstart.Text = "Start"
            btnstart.BackColor = Color.Green
        Else
            pic.Visible = False
            btnstart.Text = "Start"
            btnstart.BackColor = Color.Green
            iVal = 0
        End If

    End Sub

    Private Sub btnstart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnstart.Click
        If (btnstart.Text = "Start") Then
            btnstart.Text = "Stop"
            btnstart.BackColor = Color.Red
            pic.Visible = True
            bgw.RunWorkerAsync()
        Else
            If (bgw.IsBusy = True) Then
                btnstart.Text = "Start"
                btnstart.BackColor = Color.Green
                bgw.CancelAsync()
            End If
        End If
    End Sub
End Class