vb.net – Backgroundworker CancelAsync()不起作用

发布时间：2020-12-17 07:16:16 所属栏目：百科来源：网络整理

导读：我试图用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.愿这会有所帮助. 好吧,我添加了一些Msgbox,以了解工作者是否仍然很忙并且有线的事情是,当工人正在做事时我得到了一个错误！？！？ Publi

我试图用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.愿这会有所帮助.
好吧,我添加了一些Msgbox,以了解工作者是否仍然很忙并且有线的事情是,当工人正在做事时我得到了一个错误！？！？

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

解决方法

我认为你的问题是你只是在你的bw_DoWork方法开始时评估一次CancellationPending.由于在启动之前没有真正取消BackgroundWorker的方法,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.

为了使其工作,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做的事情.你需要从这个：

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

对于更像这样的事情：

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

（编辑：李大同）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!