WebClient.UploadProgressChanged Event

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WebClient.UploadProgressChanged Event

OSVBNET 1,401

Hello,
According to:
https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient.uploadprogresschanged

This event is raised each time an asynchronous upload makes progress, so for UploadValuesAsync and NOT for UploadValues

Is there anyway to get the progress when using UploadValues? I'm already using it inside a thread, beside that am using .NET framework 4.0 and not 4.5.
Thanks for help.

*** even this does not work:

UpClient.UploadValuesAsync(New Uri("http://www.domain.com/bb.php"), FormFields)

Private Sub UpClient_UploadProgressChanged(sender As Object, e As System.Net.UploadProgressChangedEventArgs) Handles UpClient.UploadProgressChanged
ProgressBarX.Value = e.ProgressPercentage

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Answer 1

Michael Taylor 61,226

You cannot get progress notifications from the sync version. They are blocking calls so there would be no way to respond anyway outside a separate thread.

Not sure what your intended point was around .NET 4 vs .NET 4.5. You can switch to the async version on .NET 4 if you need progress notification.

As for why your sample code isn't working, we'd need to see the full setup of the webclient. My guess is that you haven't properly hooked up the event or you did so after starting the upload.

OSVBNET 1,401 Reputation points

2022-08-22T14:54:04.533+00:00

Thanks for the tips, here's my full code:

defined at the top: Private WithEvents UpClient As New System.Net.WebClient

button_click:
Dim ThreadSend As New Thread(New ParameterizedThreadStart(AddressOf SendThread))
ThreadSend.Start()

Private Sub SendThread(MyObject As Object)
UpClient = New WebClient
UpClient.Encoding = Encoding.UTF8
UpClient.Headers.Add("user-agent", "Mozilla/5.0 (Compatible; MSIE 11.0; Windows NT 10.0; .NET CLR 4.0.30319)")
UpClient.CachePolicy = New System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore)
UpClient.UploadValuesAsync(New Uri("http://www.domain.com/bb.php"), FormFields)
End Sub

Private Sub UpClient_UploadProgressChanged(sender As Object, e As System.Net.UploadProgressChangedEventArgs) Handles UpClient.UploadProgressChanged
ProgressBarX.Value = e.ProgressPercentage
Michael Taylor 61,226 Reputation points

2022-08-22T16:37:29.72+00:00
That is your problem right there. In your SendThread function you are newing up a new webclient. That just stomped over the original one you newed up when you declared it. Since you wiped the original object the event handler you assigned to it is no longer attached. I would start with not creating a new instance of the web client in your function and see if you're suddenly getting the events again.

However another issue that I see is that your calling UploadValuesAsync but aren't wait for it to complete. Furthermore you're calling this from a separate thread which defeats the purpose of using tasks to begin with. In your button click handler simply call the web client to upload the values and return Task from the handler.

Private Async Sub button_click ( sender As Object, e As EventArgs ) await UploadValuesAsync(); ' Upload complete, now what? End Sub Private Async Sub UploadValuesAsync () UpClient.Encoding = Encoding.UTF8 UpClient.Headers.Add("user-agent", "Mozilla/5.0 (Compatible; MSIE 11.0; Windows NT 10.0; .NET CLR 4.0.30319)") UpClient.CachePolicy = New System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore) await UpClient.UploadValuesAsync(New Uri("http://www.domain.com/bb.php"), FormFields) End Sub
OSVBNET 1,401 Reputation points

2022-08-22T19:45:19.057+00:00

Thanks bud, I didn't use Async Sub/Function and didn't read the async topics, so couldn't figure it out and decided to give it up, however one thing please, you told:

newing up a new object just stomped over the original one and wiped the original object the event handler you assigned to it is no longer attached

is this a global rule in .net? I'm using a 3rd party .NET component which am using this way and declaring a new instance will not wipe the event handlers there, possible?
Michael Taylor 61,226 Reputation points

2022-08-22T20:16:26.37+00:00

is this a global rule in .net?

This is a scoping rule in pretty much every block structure language in the world. If you have a variable UpClient in scope with an assigned value and you overwrite that value by assigning a new value to it (New WebClient) then the original value is gone. Unless you have stored it elsewhere then that object is no longer available.

The .NET-specific thing is that eventually that unused object will get cleaned up by the runtime as nobody is using it. When you call UploadValuesAsync then it will raise notifications to those listeners that registered for notifications. Notifications are per instance (because each client may have a separate set of listeners). Since you created a new instance and are using it to call UploadValuesAsync there is nobody listening on it and therefore no notifications.

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WebClient.UploadProgressChanged Event

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