Backgroundworker CancelAsync() 不起作用

问题描述 投票：0回答：3

我正在尝试使用 

WorkerClass.bw.CancelAsync()
取消我的后台工作人员。但这根本行不通。

//编辑！我在这里发布了完整的代码。希望这会有所帮助。 好的，我添加了一些消息框来了解工作人员是否仍然忙碌，并且有线的事情是，当工作人员正在做事时我会收到 

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
vb.net backgroundworker
3个回答
4
投票

我认为你的问题是你只在 

CancellationPending
方法开始时评估 
bw_DoWork
一次。由于实际上没有办法在开始之前取消 
BackgroundWorker
，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 不会使用某种魔法来接管程序计数器。

为了使其发挥作用，

DoWork
方法的核心逻辑必须以允许频繁轮询
CancellationPending
的方式实现，以便代码准确地知道何时退出它正在执行的操作。你需要从这里开始：

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

对于类似这样的事情：

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
3
投票

这是BackgroundWorker的基本模型。你的样子是这样吗

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
0
投票

创建： 1 个名为“frmMain”的表单，

含 1 个名为“Button1”的按钮， 1 x 进度条，名为“ProgressBar1”。

然后将此代码粘贴到：

Imports System.ComponentModel

Public Class frmMain

' Create a BackgroundWorker instance
Private WithEvents backgroundWorker1 As New System.ComponentModel.BackgroundWorker()


Public Sub New()
    InitializeComponent()

    ' Configure the BackgroundWorker
    backgroundWorker1.WorkerReportsProgress = True
    backgroundWorker1.WorkerSupportsCancellation = True
End Sub


Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    ' Set the ProgressBar properties
    progressBar1.Minimum = 0
    progressBar1.Maximum = 100
    progressBar1.Value = 0
End Sub


' Event handler for the Start button click
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ' Cancel the BackgroundWorker if it's running
    If backgroundWorker1.IsBusy Then
        backgroundWorker1.CancelAsync()
        Button1.Text = "Start"
    Else
        backgroundWorker1.RunWorkerAsync()
        Button1.Text = "Cancel"
    End If
End Sub


' Event handler for the BackgroundWorker's DoWork event
Private Sub backgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles backgroundWorker1.DoWork
    For i As Integer = 0 To 100
        ' Check if cancellation is requested
        If backgroundWorker1.CancellationPending Then
            e.Cancel = True
            Exit For
        End If

        ' Simulate work by sleeping for a short duration
        System.Threading.Thread.Sleep(10)

        ' Report progress to the UI thread
        backgroundWorker1.ReportProgress(i)
    Next
End Sub


' Event handler for the BackgroundWorker's ProgressChanged event
Private Sub backgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles backgroundWorker1.ProgressChanged
    ' Update the ProgressBar value based on the reported progress
    progressBar1.Value = e.ProgressPercentage
End Sub


' Event handler for the BackgroundWorker's RunWorkerCompleted event
Private Sub backgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles backgroundWorker1.RunWorkerCompleted
    ' Perform any cleanup or post-processing after the backgroundWorker has either finished, or aborted

    If ProgressBar1.Value = 100 Then
        MessageBox.Show("Progress completed!")
    Else
        MessageBox.Show("Operation Aborted!")
        ProgressBar1.Value = 0
    End If
End Sub


End Class
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