vb.net - 后台 worker 不起作用... VB.Net

Question

这是我的代码:

    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    For i = 0 To 1000
        Dim inum As String = i & "0"


        Dim request As System.Net.HttpWebRequest = System.Net.HttpWebRequest.Create("http://www.google.nl/search?q=site:" & combobox1.Text & "&hl=nl&start=" & inum)
        Dim response As System.Net.HttpWebResponse = request.GetResponse

        Dim sr As System.IO.StreamReader = New System.IO.StreamReader(response.GetResponseStream())

        Dim sourcecode As String = sr.ReadToEnd
        Dim search As String = combobox1.Text
        Dim r As New System.Text.RegularExpressions.Regex("http://" & search & "/\w*")
        Dim matches As MatchCollection = r.Matches(sourcecode)


        For Each itemcode As Match In matches

            Dim item As String = (itemcode.ToString.Split("""").GetValue(0))
            Dim url As New Net.WebClient
            Dim str As String = url.DownloadString("http://www.prcheck.nl/results.php?url=" & item)

            If str.Contains(">0/10") Then
                ListBox1.Items.Add("(0/10) " & item)
            ElseIf str.Contains("1/10") Then
                ListBox1.Items.Add("(1/10) " & item)
            ElseIf str.Contains("2/10") Then
                ListBox1.Items.Add("(2/10) " & item)
            ElseIf str.Contains("3/10") Then
                ListBox1.Items.Add("(3/10) " & item)
            ElseIf str.Contains("4/10") Then
                ListBox1.Items.Add("(4/10) " & item)
            ElseIf str.Contains("5/10") Then
                ListBox1.Items.Add("(5/10) " & item)
            ElseIf str.Contains("6/10") Then
                ListBox1.Items.Add("(6/10) " & item)
            ElseIf str.Contains("7/10") Then
                ListBox1.Items.Add("(7/10) " & item)
            ElseIf str.Contains("8/10") Then
                ListBox1.Items.Add("(8/10) " & item)
            ElseIf str.Contains("9/10") Then
                ListBox1.Items.Add("(9/10) " & item)
            ElseIf str.Contains("10/10") Then
                ListBox1.Items.Add("(10/10) " & item)
            Else
                ListBox1.Items.Add("(0/10) " & item)

            End If

            Label2.Text = ListBox1.Items.Count
        Next



        If Not sourcecode.Contains("<b>Volgende</b>") Then
            MsgBox("")
            Exit For
        End If
    Next
End Sub

和combobox1.text = www.google.nl(示例)

按钮 1 的代码是:

BackgroundWorker1.RunWorkerAsync()

如果后台工作完成:

    Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    MsgBox("Done")
End Sub

如果我点击按钮 1，我会在半秒内收到消息:完成

代码有什么问题吗？

如果我将代码放在backgroundworker1中，就在button1中，它可以工作，但速度非常慢..

Answer 1

您只能从主应用程序线程内更新 UI，在这种情况下，您尝试通过后台工作线程创建的后台线程来执行此操作，这将引发您发现的异常。

您需要执行什么操作才能运行添加到主线程上的列表框的代码，您可以通过 BeginInvoke 执行此操作以及一个自定义委托(delegate)，它将您要添加的项目作为参数，然后委托(delegate)可以将项目添加到列表框 - BeginInvoke 的文档中有一个如何执行此操作的示例。