VB.Net 中 BackgroundWorker 的后期绑定问题

Question

我是运行一个 BackgroundWorker，想报告它的进度。在下面的示例中，我创建了一个测试列表，然后 BackgroundWorker 对其进行迭代。问题出在'sender.ReportProgress(i)'行。如果我启用了 Option Strict，由于后期绑定问题，它不喜欢我使用 'i'。有没有其他方法可以对此进行编码并避免该问题？

    Public Class Form1

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        ' Configuring for Background Workers
        Control.CheckForIllegalCrossThreadCalls = False

        Dim MyList As New List(Of String)
        For a As Integer = 0 To 100
            MyList.Add(CStr(a))
        Next
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Dim bgw As New System.ComponentModel.BackgroundWorker
        bgw.WorkerReportsProgress = True
        bgw.WorkerSupportsCancellation = True
        AddHandler bgw.DoWork, AddressOf bgw_DoWork
        ' I create a BackgroundWorker here rather than add one in the toolbox so that I can specify the Handler and use different Handler routines for different part of a large program.

        Button1.Enabled = False
        Dim progress As New Progress(bgw)
        progress.ShowDialog()
        Button1.Enabled = True
    End Sub

    Private Sub bgw_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs)
        For i = 0 To MyList.Count -1
            Label1.Text = MyList(i)
            sender.ReportProgress(i)
            System.Threading.Thread.Sleep(200)
            Label1.Refresh()
        Next

    End Sub

End Class


Public Class Progress
    Private WithEvents _BGW As System.ComponentModel.BackgroundWorker

    Public Sub New(ByVal BGW As System.ComponentModel.BackgroundWorker)
        _BGW = BGW
        InitializeComponent()
    End Sub

    Private Sub frmProgress_Shown(sender As Object, e As System.EventArgs) Handles Me.Shown
        If Not IsNothing(_BGW) Then
            _BGW.RunWorkerAsync()
        End If
    End Sub

    Private Sub _BGW_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles _BGW.ProgressChanged
        ProgressBar1.Value = e.ProgressPercentage
        Label1.Text = e.ProgressPercentage
    End Sub

    Private Sub _BGW_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles _BGW.RunWorkerCompleted
        Me.Close()
    End Sub
End Class

Answer 1

CType(sender, BackgroundWorker).ReportProgress(i)

Answer 2

此外，如果你想用它做多个动作，那么创建一个局部引用变量，如下所示：

Private Sub bgw_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs)

    Dim bgw As System.ComponentModel.BackgroundWorker = DirectCast(sender, System.ComponentModel.BackgroundWorker)

    ' ... now you can use "bgw" multiple times below instead of casting each time ...

    For i = 0 To MyList.Count -1
        Label1.Text = MyList(i)
        bgw.ReportProgress(i)
        bgw.SomethingElse()
        bgw.MoreStuff()
        System.Threading.Thread.Sleep(200)
        Label1.Refresh()
    Next
End Sub

显然这对您来说不是必需的，仅供参考...

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