Question

我遇到了BackgroundWorker.CancelAsync（）无效的问题。我将WorkerSupportsCancellation设置为TRUE。我也在DoWork中轮询BackgroundWorker1.CancellationPending。这是我想要实现的示例代码。我让后台工作程序循环遍历时间戳并为Measurement变量赋值。我有一个子程序，查询上次报告的Measurement变量并写入listbox。在5个循环后，我发送BackgroundWorker.CancelAsync（）。我可以看到取消正在等待，但它实际上并没有取消后台工作者。这是竞争条件吗？

Public Class Form1

Dim Measurement As String
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click

    BackgroundWorker1.RunWorkerAsync()
    Delay(0.5)

    For x = 1 To 5
        ListBox1.Items.Add(Measurement)
        ListBox1.TopIndex = ListBox1.Items.Count - 1
        TextBox1.Text = BackgroundWorker1.CancellationPending
        Delay(1)
    Next

    BackgroundWorker1.CancelAsync()

    TextBox1.Text = BackgroundWorker1.CancellationPending
    ListBox1.Items.Add("Cancel Pend: " & BackgroundWorker1.CancellationPending)
    Delay(5)
    ListBox1.Items.Add("Busy: " & BackgroundWorker1.IsBusy)

End Sub

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

    If BackgroundWorker1.CancellationPending = True Then
        e.Cancel = True
        BackgroundWorker1.Dispose()
        Exit Sub
    Else
        Do
            Measurement = Now()
        Loop
    End If

End Sub

结束班

Answer 1

你只需要在Do ...循环中移动检查取消，否则它只会在DoWork事件处理程序的开头测试，而不会在那之后进行测试

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

    If BackgroundWorker1.CancellationPending = True Then
        e.Cancel = True
        BackgroundWorker1.Dispose()
    Else
        Do
          If BackgroundWorker1.CancellationPending = True Then
            e.Cancel = True
            BackgroundWorker1.Dispose()
            Exit Do
          Else 
             Measurement = Now()
          End If
        Loop
    End if
End Sub

vb.net后台工作人员取消不工作

1 个答案: