Arrays VB.NET的WebClient错误

Question

我正在使用和将要从一个文件夹复制到另一个文件夹的文件数组，但这给我一个错误。
WebClient does not support concurrent I/O operations.

这是我的代码：

Protected Overrides Sub OnLoad(e As EventArgs)
    MyBase.OnLoad(e)
    CopyBtn.Text = "Copy File"
    CopyBtn.Parent = Me
    ProgBar.Left = CopyBtn.Right
End Sub

Dim WithEvents CopyBtn As New Button
Dim ProgBar As New ProgressBar
Dim WithEvents FileCopier As New WebClient

Private Sub CopyBtn_Click(sender As Object, e As EventArgs) Handles CopyBtn.Click

    Dim src As String = "D:\test"
    Dim dest As String = "D:\test2"

    Dim filesToCopy As New ArrayList()
    For Each Dir As String In System.IO.Directory.GetFiles(src)
        Dim dirInfo As New System.IO.DirectoryInfo(Dir)
        If Not System.IO.File.Exists(dest & "\" & dirInfo.Name) Then
            filesToCopy.Add(dirInfo.Name)
        End If
    Next

    If filesToCopy.Count > 0 Then
        If MsgBox("There are new files found. Do you want to sync it now?", MsgBoxStyle.Question + MsgBoxStyle.YesNo, "Confirm") = MsgBoxResult.Yes Then
            For i = 0 To filesToCopy.Count - 1
                CopyBtn.Enabled = False
                ProgBar.Parent = Me
                FileCopier.DownloadFileAsync(New Uri(src & "\" & filesToCopy(i)), dest & "\" & filesToCopy(i))
            Next
        End If
    Else
        MsgBox("No new files to be copied")
    End If

End Sub
Private Sub FileCopier_DownloadProgressChanged(sender As Object, e As DownloadProgressChangedEventArgs) Handles FileCopier.DownloadProgressChanged
    Dim bytesIn As Double = Double.Parse(e.BytesReceived.ToString())
    Dim totalBytes As Double = Double.Parse(e.TotalBytesToReceive.ToString())
    Dim percentage As Double = bytesIn / totalBytes * 100
    ProgBar.Value = Int32.Parse(Math.Truncate(percentage).ToString())
End Sub
Private Sub FileCopier_DownloadFileCompleted(sender As Object, e As System.ComponentModel.AsyncCompletedEventArgs) Handles FileCopier.DownloadFileCompleted
    ProgBar.Parent = Nothing
    CopyBtn.Enabled = True
End Sub

但是当我将这段代码放在复制/下载文件异步之前
Dim FileCopier as WebClient = New Webclient
成功复制。 但是进度条不起作用，
即使我把它放在DownloadProgressChanged
ProgBar.Value = e.ProgressPercentage
它不会加载。 你能帮我么？ 只是一个新手还在这里学习。

Answer 1

哇，我只需要添加这个
AddHandler FileCopier.DownloadProgressChanged, AddressOf FileCopier_DownloadProgressChanged AddHandler FileCopier.DownloadFileCompleted, AddressOf FileCopier_DownloadFileCompleted
使用以下代码：
Dim FileCopier as WebClient = New Webclient
ProgBar.Value = e.ProgressPercentage