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Goyo
Asked: 2020-04-29 13:42:45 +0800 CST 2020-04-29 13:42:45 +0800 CST

Catch WebException on Asynchronous request

  • 772

I am making asynchronous requests and I am storing them in a list Task, at the end of the iteration, that is, since it sends all the requests, I use the method WhenAll().Resultto capture all the responses once the requests have finished and save them in an array, as shown in the following code:

try
{
   IEnumerable<Task<string>> task = requestArray.Select((a, i) =>
   {
       var fareIds = new List<string>();
       var ticketsId = new List<string>();
       var seatsNumber = new List<string>();

       for (var posSeat = 0; posSeat < requestArray[i].seats.Length; posSeat++)
       {
           fareIds.Add(requestArray[i].seats[posSeat].fareId.ToString());
           ticketsId.Add(requestArray[i].seats[posSeat].ticketId.ToString());
           seatsNumber.Add(requestArray[i].seats[posSeat].number.ToString());
        }

        var xml = BlockSeatRQ(i, seatsNumber.ToArray(), fareIds.ToArray(), ticketsId.ToArray(), tokenRQ);

        WebClient client = new WebClient();
        client.Headers.Add("Content-Type", "application/xml");

        return Task.Run(() => client.UploadStringTaskAsync(Config.Endpoint + SEAT_BLOCK_URL, "POST", xml));
   });

   blockSeatResponses = Task.WhenAll(task).Result;       
}
catch (WebException e)
{


}

The problem I have is that when an exception arises, it does not enter the catch, but rather it thunders when the method WhenAllis called, as shown in the following image:

enter image description here

Now the question is, why doesn't it enter the catch? And how can I make it enter the catch? Since the service I am using does not return a specific error to use, it simply allows me to enter Exceptionand get the error message.WebExceptionBody

I hope you understand the problem.

c#

1 Answers

  1. Best Answer

    It does not enter catchbecause you are only catching exceptions of the type WebExceptionand in that case what you mark in your image is throwing one of the type AggregateException. So far the reason.

    If you want to treat your exceptions specifically you must stack catches with each type and its exclusive treatment, it is always good practice at the end of all the catches to catch the ones of the type Exceptionso your application would not throw an unhandled exception error.

    An example:

    try
{ 
    //...aquí algún código que probablemente lanze excepción
}
catch(WebException we)
{
    //aquí trato las excepciones del tipo WebException
}
catch(AggregateException ae)
{
    //aquí trato las excepciones AggregateException
    //en tu caso entraría a este catch
}
catch(Exception e)
{
    //aquí trato las excepciones que no ingresaron en
    //los otros catch
}

    EDITED:

    To avoid it AggregateExceptionyou can use:

    blockSeatResponses = await Task.WhenAll(task);

    awaitreturns the resultdel taskand unwraps the AggregateException.

    • 1