Assembly: System (in System.dll)
'Declaration Public Delegate Sub UploadFileCompletedEventHandler ( _ sender As Object, _ e As UploadFileCompletedEventArgs _ )
When you create a delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event handler delegates, see Events and Delegates.
The following code example demonstrates asynchronously uploading a file.
' Sample call: UploadFileInBackground("http:' www.contoso.com/fileUpload.aspx", "data.txt") Public Shared Sub UploadFileInBackground(ByVal address As String, ByVal fileName As String) Dim waiter As System.Threading.AutoResetEvent = New System.Threading.AutoResetEvent(False) Dim client As WebClient = New WebClient() Dim method As String = "POST" Dim uri as Uri = New Uri(address) ' Specify that that UploadFileCallback method gets called ' when the file upload completes. AddHandler client.UploadFileCompleted, AddressOf UploadFileCallback client.UploadFileAsync(uri, method, fileName, waiter) ' Block the main application thread. Real applications ' can perform other tasks while waiting for the upload to complete. waiter.WaitOne() Console.WriteLine("File upload is complete.") End Sub
The following method is called when the upload completes.
Private Shared Sub UploadFileCallback(ByVal sender As Object, ByVal e As System.Net.UploadFileCompletedEventArgs) Dim waiter As System.Threading.AutoResetEvent = CType(e.UserState, System.Threading.AutoResetEvent) Try Dim reply As String = System.Text.Encoding.UTF8.GetString(e.Result) Console.WriteLine(reply) Finally ' If this thread throws an exception, make sure that ' you let the main application thread resume. waiter.Set() End Try End Sub