Download cancel delay in Xamarin Forms

Question

I need to download a pdf file and save in device. I have used WebClient process to download a file and show progress while downloading it.

CancellationTokenSource Token= new CancellationTokenSource(); //Initialize a token while start download
webClient.DownloadFileTaskAsync(new Uri(downloadurl), saveLocation); // Download file

Download is working properly. To cancel the download which is in progress, I have used cancellationtokensource as mentioned in below link.

https://learn.microsoft.com/en-us/dotnet/standard/threading/cancellation-in-managed-threads

Token.Cancel(); //Cancellation download

try
{
// check whether download cancelled or not
Token.ThrowIfCancellationRequested();
if(Token.IsCancellationRequested)
{
  //Changed button visibility
}
}
catch (OperationCanceledException ex)
{
}

It takes more seconds to cancel the download. Can you please suggest me to reduce the delay in cancelling download?

Could you please post the complete code that cancel the download task? — York Shen, Oct 29 '17 at 10:23

score 0 · Accepted Answer · answered Nov 08 '17 at 04:33

We have to register token into webclient cancel async process before downloadasync process. We have to maintain order like below,

//Initialize for download process
WebClient webClient = new WebClient();
CancellationTokenSource token = new CancellationTokenSource();

//register token into webclient
token.Register(webClient.CancelAsync);
try
{
  webClient.DownloadFileTaskAsync(new Uri(downloadurl), saveLocation); // Download a file
}
catch(Exception ex)
{
  //Change button visibility
}

Token.Cancel(); //Cancellation download put in cancel click button event

It doesn't takes even milliseconds and cancellation works fine in both Xamarin.Android and Xamarin.iOS device.

Download cancel delay in Xamarin Forms

1 Answers1