VB.Net中的BackgroundWorker的后期绑定问题

我正在运行一个BackgroundWorker，并且想要报告它的进度。在下面的例子中，我创建了一个BackgroundWorker然后迭代的测试列表。问题在于'sender.ReportProgress（i）'这一行。如果我有Option Strict选项，它不会因为延迟绑定问题而使用'i'。有没有其他的方法来编码，并避免这个问题？VB.Net中的BackgroundWorker的后期绑定问题

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

来源

2017-05-29 Tim Makins

它不是'我'它有问题，它是'ReportProgress'方法 - 'System.Object'没有这样的方法。还有其他几个问题。在旁注中，您应该访问[游览]页面 - 您的过去3个帖子有5个答案，但全部保持打开状态，因为没有答案被接受， – Plutonix

感谢您的意见。还有什么其他问题？确定接受 - 我没有意识到我应该这样做。 –

CType(sender, BackgroundWorker).ReportProgress(i)

来源

2017-05-29 15:10:08 Mike

请注意：使用[**'DirectCast' **]（https://docs.microsoft.com/en-us/dotnet/articles/visual-basic/language-reference）会更好（也更快） /运营商/ directcast运营商）当对象类型是已知的。 'CType'应该在转换为_ **不同的** _类型时使用（例如将一个Byte转换为一个Integer，尽管这通常在不使用Option Strict时隐式完成）。 –

两者之间的区别在于'CType'尝试使用[**转换运算符**]（https://docs.microsoft.com/zh-cn/dotnet/articles/visual-basic/programming-guide/language -features/procedures/how-to-define-a-conversion-operator）来执行转换，如果失败，它会尝试转换。 ''DirectCast'只能进行转换，因此当你不想将一个对象转换为另一种类型时，它比'CType'快得多。 –

另外，如果你想用它做多个动作，然后创建一个像这样的局部引用变量：

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，这不是你的情况需要的，只是一个仅供参考...

来源

2017-05-29 16:12:35

VB.Net中的BackgroundWorker的后期绑定问题

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