Question

我正在尝试使用WorkerClass.bw.CancelAsync()取消我的Backgroundworker。但它根本不起作用。

//编辑！我在这里发布了完整的代码。愿这会有所帮助。好的，我添加了一些Msgbox，以了解工作者是否仍然忙碌而有线的事情是，当工人正在做事时我得到false！？

Public Class Form1

Private Sub btn_start_click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_start.Click
        Dim WorkerClass As New BGWClass
        WorkerClass.bw.WorkerSupportsCancellation = True
        WorkerClass.bw.WorkerReportsProgress = True
        If btn_start.Text = "Start" Then
            btn_start.Image = My.Resources.Resources.gem_remove
            btn_add_addy.Enabled = False
            btn_start.Text = "Stop"
            WorkerClass.Start()
            WorkerClass.bw.RunWorkerAsync()
            MsgBox(WorkerClass.bw.IsBusy & " " & WorkerClass.bw.WorkerSupportsCancellation)
        Else
            btn_start.Image = My.Resources.Resources.error_fuck
            btn_add_addy.Enabled = True
            btn_start.Enabled = False
            MsgBox(WorkerClass.bw.IsBusy & " " & WorkerClass.bw.WorkerSupportsCancellation)
            WorkerClass.bw.CancelAsync()
        End If
    End Sub
End Class

Public Class BGWClass
    Public bw As BackgroundWorker = New BackgroundWorker

    Sub Start()
        AddHandler bw.DoWork, AddressOf bw_DoWork
        AddHandler bw.ProgressChanged, AddressOf bw_ProgressChanged
        AddHandler bw.RunWorkerCompleted, AddressOf bw_RunWorkerCompleted
    End Sub

    Private Sub bw_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs)
         For x As Integer = 1 To 15
            If bw.CancellationPending Then
                e.Cancel = True
                Exit Sub
            End If
            bw.ReportProgress(x)
            Threading.Thread.Sleep(1000)
        Next
    End Sub

    Private Sub bw_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs)
        Dim myObject As Object = e.UserState
        Form1.Prgs_error.Text = "- Error: " + e.ProgressPercentage.ToString
    End Sub

    Private Sub bw_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs)
        '...
    End Sub
End Class

Answer 1

我认为您的问题是，您只是在CancellationPending方法开始时评估bw_DoWork一次。由于在BackgroundWorker开始之前没有真正取消CancellationPending的方法，CancelAsync将始终为假，并且永远不会中断工作。当您致电DoWork时，BackgroundWorker不会使用某种魔法来接管程序计数器。

为了使其正常工作，CancellationPending方法的核心逻辑必须以允许频繁轮询Private Sub bw_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) If bw.CancellationPending = True Then e.Cancel = True Else 'do stuff here End If End Sub的方式实现，以便代码准确知道何时到退出它正在做的事情。你需要离开这个：

Private Sub bw_DoWork(ByVal sender As Object, 
                      ByVal e As System.ComponentModel.DoWorkEventArgs)

    Dim workIsCompleted As Boolean = False
    While (Not bw.CancellationPending) AndAlso (Not workIsCompleted) Then

        ' Do stuff here, but incrementally so that the while loop can
        ' periodically check to see if CancelAsync has been called.
        ' Also, be sure to set workIsCompleted = True when the work is done.
        ' Otherwise, you will just spin forever until someone cancels it
        ' (Which may or may not be a bad thing, depending on your requirements)

    End While

End Sub

更像这样的事情：

{{1}}

Answer 2

这是BackgroundWorker的基本模型。这是你的样子。

Dim WithEvents worker As New System.ComponentModel.BackgroundWorker

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    'start
    If Not worker.IsBusy Then
        worker.WorkerReportsProgress = True
        worker.WorkerSupportsCancellation = True
        worker.RunWorkerAsync()
    End If
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    'cancel
    If worker.IsBusy AndAlso worker.WorkerSupportsCancellation Then
        worker.CancelAsync()
    End If
End Sub

Private Sub foo_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles worker.DoWork
    For x As Integer = 1 To 15
        If worker.CancellationPending Then
            e.Cancel = True
            Exit For
        End If
        worker.ReportProgress(x)
        Threading.Thread.Sleep(1000)
    Next
End Sub

Private Sub foo_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles worker.ProgressChanged
    Label1.Text = e.ProgressPercentage.ToString
End Sub

Private Sub foo_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles worker.RunWorkerCompleted
    If e.Cancelled Then
        Label1.Text = "canceled"
    ElseIf Not IsNothing(e.Error) Then
        Label1.Text = "error " & e.Error.Message
    Else
        Label1.Text = "done"
    End If
End Sub

Backgroundworker CancelAsync（）不起作用

2 个答案: