Vb.net Backgroundworker CancelAsync（）赢了'；行不通

我正试图用

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。希望这会有帮助。 好的，我添加了一些MSGBoxe，以了解工作人员是否仍然很忙，而有线的事情是，当工作人员在做事情时，我会得到一个

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

---

下面是后台工作人员的基本模型。这就是你的样子

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

---

我认为您的问题在于，在

bw\u-DoWork

方法开始时，您只评估了

CancellationPending

一次。由于在

BackgroundWorker

启动之前没有真正的方法来取消它，因此

CancellationPending

将始终为false，并且永远不会中断工作。当您调用

CancelAsync

时，BackgroundWorker不会使用一些魔法来接管程序计数器

为了使其工作，您的

DoWork

方法的核心逻辑必须以允许频繁轮询

CancellationPending

的方式实现，以便代码能够准确地知道何时退出正在执行的操作。您需要从以下方面着手：

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

更像这样：

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

---

您是否设置了

WorkerClass.bw.workerSupportsScanCellation=True

？否则它不会取消任何东西。你能把整个backgroundworker代码放进去吗？我放了。你能再看一遍吗？）Allready添加了这个部分。取消支票不是问题。它很好用。我的问题是，工作人员告诉我它不忙？你能在按钮点击处理程序中输入一个，并确认

CancelAsync

甚至被调用吗？不完全正确，但大多数情况下这应该与我的代码相同。所有的工作，尤其是

CancelAsync（）

好的，我试着用你的来编辑我的，我总是得到

worker.IsBusy的布尔值false。不知道为什么，因为工人在工作？！在后台工作程序实际启动并将属性更新为
True
之前，从调用RunWorkerAsync开始可能会有延迟。生成新线程并开始执行代码需要时间。您在下一行中选中的
IsBusy
（再次，一次且仅一次）可能发生在任何一行完成之前。如果你任意延迟（比如3000毫秒），那么它可能会工作。好的，你是对的。但这仍然没有解决我的问题。我还是不能取消那个工人的工作。即使在下一个语句中使用了一个简单的