Question

使用以下VB.Net简单代码在FTP上传文件，调用WebClient.CancelAsync（）实际上不会取消上传。

有人知道为什么，可以做些什么呢？

Private Sub UploadProgressChanged(ByVal sender As Object, ByVal e As System.Net.UploadProgressChangedEventArgs)
    'TO-DO: Why is pbar empty?
    ProgressBar1.Value = e.ProgressPercentage

    Label1.Text = e.BytesSent & " bytes sent"
End Sub

Private Sub UploadFileCompleted(ByVal sender As Object, ByVal e As System.Net.UploadFileCompletedEventArgs)
    MessageBox.Show("Done!")
    Button1.Text = "Upload"
    ProgressBar1.Value = 0
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim client As New WebClient

    If Button1.Text = "Cancel" Then
        'TO-DO: Doesn't actually cancel upload!
        client.CancelAsync()

        Button1.Text = "Upload"
        ProgressBar1.Value = 0
    Else
        Button1.Text = "Cancel"

        Const MYFILE = "big.file.bin"
        Const LocalFile As String = "C:\" & MYFILE

        Dim RemoteFile As String = "ftp://upload.acme.com/" & MYFILE

        client.Credentials = New NetworkCredential("anonymous", "test")
        client.Proxy = Nothing

        AddHandler client.UploadFileCompleted, AddressOf UploadFileCompleted
        AddHandler client.UploadProgressChanged, AddressOf UploadProgressChanged

        ProgressBar1.Maximum = 100

        Try
            client.UploadFileAsync(New Uri(RemoteFile), LocalFile)
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try

        client.Dispose()
    End If
End Sub

谢谢。

Answer 1

我自己不使用VB，但它看起来像是在错误的客户端上调用client.cancelAsync（）。

每次按取消/上传按钮时，您都会创建一个新客户端。

如果要取消启动的第一个客户端，则需要在click_handler外部实例化它。

另外，为什么使用按钮标签检查是否应取消客户端？

如果是client.IsBusy ......

，你可以这样做

使用WebClient取消上传？

1 个答案: