VB.Net 后台工作者

Question

我使用 Visual Studio 2013 for Visual Basic，我正在努力调试我的多线程程序。

我正在使用 BackgroundWorker，它的工作方式似乎与我认为的不同。

我不明白为什么我的程序在仅处理 ArrayList 中名为 arFileName 的第一个条目后就停止了。

BackgroundWorker1.DoWork 过程中的 For Each 语句无法遍历以下代码中的整个 arFileName：

Private Sub btnRun_Click(sender As Object, e As EventArgs) Handles btnSelectCsv.Click

    'arFileName is ArrayList and it has enormous counts
    ProgressBar1.Maximum = arFileName.Count

    Me.Cursor = Cursors.WaitCursor

    'Do background
    BackgroundWorker1.RunWorkerAsync()

    Me.Cursor = Cursors.Arrow

    MessageBox.Show("Finished!", "info", MessageBoxButtons.OK, MessageBoxIcon.Asterisk)


End Sub


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

    Dim arNotFoundFile As New ArrayList

    'Confirm file exists
    For Each filename As String In arFileName ' Here!
        If Not IO.File.Exists(filename) Then

            arNotFoundFile.Add(filename)
            ProgressBar1.Value = ProgressBar1.Value + 1
        End If
    Next

End Sub

Answer 1

后台程序必须设置为报告其进度

 BackgroundWorker1.WorkerReportsProgress = True

那么，典型的实现方式如下：

Dim progress As Integer = 0

Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    While (progress < 100)
        ' YOUR CODE HERE
        progress += 1
        BackgroundWorker1.ReportProgress(progress)
    End While
End Sub

Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
    ' YOUR PROGRESSBAR VALUE HERE, USING progress VARIABLE
End Sub

Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    MessageBox.Show("Work completed")
End Sub

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    BackgroundWorker1.WorkerReportsProgress = True
    BackgroundWorker1.RunWorkerAsync()
End Sub

如您所见，我定义了一个 progress 变量，它将跟踪已完成工作的百分比。在我们使用 RunWorkerAsync 启动 backgroundworker（我在 Form_Load 事件中执行此操作）后，我们可以通过ProgressChanged 事件：在这里，我们使用由我们的工作修改的进度变量 (DoWork)。您可以使用它来设置进度条值属性。最后，当所有这些都完成后，我们将消息发送到适当的事件中，即 RunWorkerCompleted

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