Cancelling upload with WebClient? - vb.net

Question

Using the following VB.Net simple code to upload files in FTP, a call to WebClient.CancelAsync() doesn't actually cancel the upload.
Does someone know why, and what can be done about this?
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
Thank you.

Answer 1

I don't use VB myself but it looks to me like you are calling client.cancelAsync() on the wrong client.
You are making a new client each time you press the cancel/upload button.
If you want to cancel the first client you started you need to instantiate it externally to the click_handler.
Also why are you using the button label to check if the client should be cancelled?
You can do if client.IsBusy ...